HomeMy WebLinkAbout23-08-31 Naalehu Preliminary Engineering Report
Naalehu Large Capacity
Cesspool Closure Project
Revised Preliminary
Engineering Report
Prepared for
County of Hawaii, Department of
Environmental Management
August 2023
2261 Aupuni Street, Suite 201
Wailuku, Maui, HI 96793
T: 808.244.7005
August 31, 2023
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
108 Railroad Avenue
Hilo, HI 96720 153740.008
Subject: Naalehu Wastewater Treatment Plant Revised Preliminary Engineering Report
Dear Ms. Iokepa-Moses:
Brown and Caldwell (BC), in association with Engineering Partners, Inc. (EPI) is pleased to
present the attached Revised Preliminary Engineering Report (PER) for the Naalehu
Large Capacity Cesspool (LCC) Closure Project. Preparation of a Revised PER is required
by the Revised Administrative Order on Consent (AOC) that became effective on
August 22, 2022. The need for a Revised PER was precipitated by several items:
· A wastewater treatment process with a smaller and shallower footprint is preferable
due to the presence of lava rock at the proposed wastewater treatment plant (WWTP)
site. Mechanical treatment technologies in the form of package plants offer the
opportunity to achieve these goals.
· The community, through community meetings and outreach, has not been receptive
to the aerated lagoon technology that was formerly proposed.
· The Revised AOC allows the possibility of implementing individual wastewater systems
(IWS) to close the LCCs.
The Revised AOC requires evaluation of four feasible options:
i. A package plant and new collection system.
ii. A package plant connected to the existing collection system.
iii. A maintenance contract model IWS program.
iv. An operating permit model IWS program.
This Revised PER consists of three parts:
· This introductory summary that provides comparisons of the four feasible options.
· Part A, by BC, which presents updated analysis of feasible options i and ii that are
based on using a package plant based WWTP to service the Naalehu community and
close the LCCs. BC is a nation-wide environmental engineering firm with local Hawaii
offices located in Kamuela, Wailuku, and Honolulu. BC has been planning and
designing WWTPs throughout the United States for over 75 years.
· Part B, by EPI, which presents a detailed analysis of feasible options iii and iv that are
based on using IWS to service the Naalehu community and close the existing LCCs.
EPI is a multi-discipline engineering and design firm based in Hilo. EPI has
successfully designed IWS systems on Hawaii Island and is well-versed to address
implementing IWS in the unique local soil and subsurface geological conditions in
Naalehu.
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 2
Throughout this Revised PER the following terms are used:
“Feasible options” refers to the four specific options (i, ii, iii, iv) listed
above and in paragraph V.A.31.a of the Revised AOC.
“Alternatives” and “project alternatives” refer to various combinations of
systems or technologies that are evaluated within this Revised PER to
determine preferences for the feasible options.
1. Comparison of Feasible Options
The four feasible options are compared below,
1.1 Protection of Human Health and the Environment
Table 1 compares the four feasible options with respect to protection of human health
and the environment. The State of Hawaii Department of Health (DOH) regulates both
WWTPs and IWS. All four feasible options are protective of human health and the
environment when implemented in accordance with the applicable Hawaii Administrative
Rules (HAR). Additional discussion is provided in Parts A and B.
Table 1. Protection of Human Health and the Environment
Feasible Option Regulatory Authority Variances
Protective of
Human Health and
the Environment?
i. Package plant and new
collection system HAR 11-62, Subchapter 2 Variance required by DOH for WWTP
flow capacity Yes
ii. Package plant connected to
the existing collection system HAR 11-62 Subchapter 2 Variance required by DOH for WWTP
flow capacity Yes
iii. A maintenance contract
model IWS program HAR 11-62, Subchapter 3 Variances may be required for some
lots for setback distances, etc. Yes
iv. An operating permit model
IWS program HAR 11-62, Subchapter 3 Variances may be required for some
lots for setback distances, etc. Yes
1.2 Capital Cost Comparison of Feasible Options
Table 2 summarizes the capital costs for the four feasible options. Details of the capital
cost estimates are provided in Parts A and B. Note that the IWS capital costs per lot are
presented as ranges; greater precision will not be available until designs are complete
due to the site-specific nature of IWS implementation on existing developed properties.
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 3
Table 2. Capital Cost Comparison
Feasible Option Capital Cost ($ million) Cost per Lot
i. Package plant and new collection system $84.3 $413,000 a
ii. Package plant connected to the existing collection system $74.2 $364,000 a
iii. A maintenance contract model IWS program $5.8 - $29.1 $30,000 - $150,000 b
iv. An operating permit model IWS program $5.8 - $29.1 $30,000 - $150,000 b
a. Based on a total of 204 lots in the WWTP service area.
b. Based on a total of 194 lots converted per the AOC.
As shown in the table, the IWS feasible options incur significantly lower capital costs than
the package plant alternatives.
1.3 Long-Term Recurring Costs Comparison
Long-term recurring costs include operations and maintenance (O&M) costs; examples
include labor, electricity, chemicals, and maintenance materials like spare parts. Another
recurring cost is the need to replace and refurbish (R&R) equipment or systems when
they reach the end of their useful life.
A summary of the long-term recurring costs for the four feasible options is presented in
Table 3 for comparison. Additional detail is included in Parts A and B.
Table 3. Long-Term Recurring Costs Comparison
Feasible Option Annual O&M Cost a R&R Cost (after 20 years) a
i. Package plant and new collection system $886,000 $6,000,000
ii. Package plant connected to the existing collection system $1,050,000 $6,000,000
iii. A maintenance contract model IWS program $250,000 $5,800,000
iv. An operating permit model IWS program $340,000 $5,800,000
a. Expressed in current (2023) dollars.
1.4 Life-Cycle Cost Comparison
An economic evaluation was prepared to assess the potential life-cycle costs associated
with each project alternative. The economic evaluation consists of a net present value
comparison. The net present value analysis includes capital, O&M, and R&R costs. An
appropriate inflationary factor and discount rate are applied to obtain the net present
value over a 30-year planning period. The net present value of an alternative represents
the amount of money that would need to be set aside today (at a given interest rate) to
pay the costs associated with the alternative over the entire planning period. The
alternative with the lowest net present value is considered the most attractive from an
economic perspective. Table 4 summarizes the life-cycle cost evaluation assumptions.
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 4
Table 4. Life-Cycle Economic Assumptions
Description Value
Year of analysis 2023
Planning period 30 years
Inflation rate 3.5 percent
Discount rate 5.0 percent
R&R cycle 20 years
Table 5 presents the life-cycle cost evaluation results.
Table 5. Life-Cycle Cost Evaluation Results
Alternative Capital
Cost ($M)
Net Present Value of O&M and R&R
Costs ($M)
Life-Cycle
Cost ($M)
i. Package plant and new collection system $84.3 $ 25.4 $ 109.8
ii. Package plant connected to the existing
collection system $74.2 $ 29.3 $ 103.5
iii. A maintenance contract model IWS program $ 29.1 $ 10.2 a $ 39.3
iv. An operating permit model IWS program $ 29.1 $ 12.3 a $ 41.4
a Includes replacement costs and IWS O&M costs paid directly by homeowners.
Figure 1 shows the results graphically. The IWS alternatives have significantly lower life-
cycle costs than the package plant alternatives.
Figure 1. Life-Cycle Cost Comparison
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 5
Figure 2 shows the cumulative cash flow projections for the four feasible alternatives
over the planning period, expressed in current (2023) dollars.
Figure 2. Cumulative Cash Flow Projections
1.5 Schedule
The Revised AOC requires the LCCs be closed no later than December 31, 2027. Parts A
and B include preliminary assessments of implementation schedules. Table 6 provides a
summary of the preliminary implementation schedule assessments. As discussed in Part
A, it will be difficult to implement the WWTP approach to close the LCCs by the deadline,
due to entitlement processes, environmental review, land acquisition, and materials
supply challenges currently facing the Hawaii construction industry. A design/build
approach could potentially reduce the implementation timeframe if equipment
procurement and fabrication can occur in parallel with design. However, compliance with
the Revised AOC deadline will be a significant challenge with Feasible Options i and ii
without a schedule extension.
Per Part B, the IWS approach may be able to be implemented by the Revised AOC
deadline. The IWS approach assumes that the County can address Hawaii Revised
Statues (HRS) 343 environmental review requirement via an exemption, and that
property access and any alterations to County regulations deemed necessary by the
County are achievable within the timeframe.
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 6
Table 6. Summary of Preliminary Implementation Schedule Assessments
Description
Feasible Options
i.
Package Plant
New Collection
System
ii.
Package Plant
Existing
Collection System
iii.
Maintenance
Contract Model
IWS Program
iv.
Operating
Permit Model
IWS Program
Entitlements and permitting Q4 2024 Q4 2024 Q2 2024 Q2 2024
Design and construction Q3 2028 Q3 2028 Q2 2026 Q2 2026
Estimated LCC closure Q3 2028 Q3 2028 Q3 2026 Q3 2026
Revised AOC LCC closure milestone December 31, 2027
Risk of missing Revised AOC LCC closure
milestone High High Moderate Moderate
Note: Q = quarter
2. Revised AOC References
The Revised AOC paragraph V.30.A.a lists information that must be included in this
Revised PER. Table 7 provides references to the information within.
Table 7. Revised AOC Paragraph V.30.A.a Checklist
Revised AOC
Paragraph V.30.A.a
Description
Report Reference Section for Feasible Options
i.
Package Plant
New Collection
System
ii.
Package Plant
Existing Collection
System
iii.
Maintenance
Contract Model
IWS Program
iv.
Operating Permit
Model IWS
Program
Description of project details for
each feasible option
Part A, §2.3, §2.4,
and §8
Part A, §2.3 and §8 Part B, §10 Part B, §10
Planning area description Part A, Fig. 2-1 Part A, Fig. 2-1 Part A, Fig. 2-1 Part A, Fig. 2-1
Planning period Part A, §7.2.3 Part A, §7.2.3 Part A, §7.2.3 Part A, §7.2.3
Description of planning phases Part A, §7.2.3 Part A, §7.2.3 Part A, §7.2.3 Part A, §7.2.3
Owner and operator of facilities Part A, §1-1 Part A, §1-1 County/In-house or
3rd-party service
provider
Homeowner/3rd-
party service
provider
Location of facilities (including a
map)
Part A, Fig. 2-1,
Fig. 8-1
Part A, Fig. 2-1,
Fig. 8-1
Part A, Fig. 2-1 Part A, Fig. 2-1
Design parameters for each feasible
option
Part A, §2.3, §2.4,
and §8
Part A, §2.3, and §8 Part B, Table 1.10 Part B, Table 1.10
Major unit processes: Part A, §5 Part A, §5 Part B, §10 Part B, §10
Flow diagram Part A, Fig. 8-2 Part A, Fig. 8-2 Part B, Fig. 1.1 Part B, Fig. 1.1
Pipe lengths, sizes, and locations Part A, Appendix D Part A, Appendix D Part B, Appendix F Part B, Appendix F
Design criteria Part A, §8.3 Part A, §8.3 Part B, §6 Part B, §6
Project costs Part A, §7 Part A, §7 Part B, §11,
Appendix B
Part B, §11,
Appendix B
Ms. Brenda Iokepa-Moses
County of Hawaii Wastewater Division
August 31, 2023
Page 7
3. Conclusions
From a technical perspective, all four feasible options represent viable ways to close the
LCCs in Naalehu and will be protective of human health and the environment. The IWS
feasible options (iii and iv) present significantly lower capital, long-term recurring, and
life-cycle costs than the WWTP feasible options (i and ii). In addition, the IWS feasible
options (iii and iv) offer greater potential to meet the LCC closure deadline contained
within the Revised AOC. We anticipate that financing options, community engagement,
burden on the Naalehu community, and alignment with County long term planning goals
will need to be considered outside of this preliminary engineering report.
The County provided the following statement:
“COH will continue working with, planning department, community leaders, and
developers for long term accomplishments of the CDP as this will take more time and
effort than what was given within the AOC. Better planning decisions can be made as the
COH can continue monitoring growth, work with planning department on the general
plan 2045, finalize the cesspool conversion master plans, and be able to negotiate a
better financial plan with all stakeholders aka developers, businesses, state government
agencies, and the community at large.”
Brown and Caldwell appreciates that the County has requested our services in assisting
with this project. Should you have any questions, please do not hesitate to call Craig
Lekven at 808.442.3301.
Very truly yours,
Brown and Caldwell
Craig C. Lekven, P.E., Project Manager
Wailuku, Hawaii
PART A: WWTP Approach
Part A
Naalehu Wastewater Treatment Plant
Revised Preliminary Engineering Report
Prepared for
County of Hawaii, Department of Environmental Manag ement
August 20 2 3
THIS WORK (PART A) WAS PREPARED BY ME OR UNDER MY S UPERVISION
April 30, 2024
Signature Expiration Date of the License
iii
Table of Contents–Part A
List of Figures .............................................................................................................................................. vi
List of Tables ............................................................................................................................................... vii
List of Abbreviations .................................................................................................................................. viii
1. Introduction .......................................................................................................................................1-1
1.1 Background .............................................................................................................................1-1
1.2 Existing System .......................................................................................................................1-1
1.3 Report Contents ......................................................................................................................1-2
2. Collection System ..............................................................................................................................2-1
2.1 Service Area ............................................................................................................................2-1
2.2 Existing Collection System .....................................................................................................2-3
2.3 Phase 1 Collection System Project ........................................................................................2-3
2.4 Phase 2 Collection System Project ........................................................................................2-5
2.5 Collection System Alternatives...............................................................................................2-5
2.6 Collection System Costs .........................................................................................................2-6
2.7 Recommendation ...................................................................................................................2-8
3. Flow and Load Projections ................................................................................................................3-1
3.1 Flow Projections Based on City and County of Honolulu Standards ...................................3-1
3.2 Reduced Flows Based on Potable Water Records ...............................................................3-1
3.2.1 Dry Weather I/I Allowance .......................................................................................3-2
3.2.2 Wet Weather I/I Allowance ......................................................................................3-2
3.2.3 Reduced Flow Projections ........................................................................................3-2
3.2.4 Flow Variance ...........................................................................................................3-3
3.3 Influent Characteristics ..........................................................................................................3-3
3.4 Influent Mass Loads ...............................................................................................................3-3
4. Effluent Management Alternatives and Regulatory Requirements ...............................................4-1
4.1 Effluent Management Alternatives ........................................................................................4-1
4.1.1 Ocean Discharge ......................................................................................................4-1
4.1.2 Subsurface Disposal via Injection Wells .................................................................4-1
4.1.3 Water Recycling ........................................................................................................4-2
4.1.4 Slow Rate Land Treatment ......................................................................................4-3
4.1.5 Subsurface Drip Irrigation Disposal ........................................................................4-3
4.1.6 Leach Field ................................................................................................................4-4
4.1.7 Ramifications of United States Supreme Court Opinion on County of Maui,
Hawaii v. Hawaii Wildlife Fund et. al. ......................................................................4-4
4.1.8 Recommendation .....................................................................................................4-7
Naalehu WWTP Revised PER Table of Contents
iv
4.2 Treatment Requirements .......................................................................................................4-8
5. Wastewater Treatment Evaluations .................................................................................................5-1
5.1 Preliminary Treatment ............................................................................................................5-1
5.1.1 Influent Flow Measurement .....................................................................................5-1
5.1.2 Influent Flow Sampling .............................................................................................5-1
5.1.3 Screening ..................................................................................................................5-1
5.1.4 Grit Removal .............................................................................................................5-2
5.1.5 Odor Control ..............................................................................................................5-7
5.1.6 Recommendation .....................................................................................................5-8
5.2 Secondary Treatment .............................................................................................................5-9
5.2.1 Membrane Bioreactor ..............................................................................................5-9
5.2.2 Sequencing Batch Reactor ................................................................................... 5-10
5.2.3 Nereda (Granular Activated Sludge) Process ...................................................... 5-11
5.2.4 Oxidation Ditch ...................................................................................................... 5-11
5.2.5 Extended Aeration Activated Sludge Package Plant ........................................... 5-12
5.2.6 Activated Sludge with Anoxic Selector ................................................................. 5-13
5.2.7 Recirculating Gravel Filter ..................................................................................... 5-13
5.2.8 Secondary Treatment Technology Screening ...................................................... 5-14
5.3 Disinfection .......................................................................................................................... 5-16
5.3.1 Sodium Hypochlorite ............................................................................................. 5-16
5.3.2 Calcium Hypochlorite ............................................................................................ 5-18
5.3.3 Ultraviolet Light Disinfection ................................................................................. 5-19
5.3.4 Cost Evaluation ...................................................................................................... 5-20
5.3.5 Disinfection Recommendation ............................................................................. 5-20
6. Solids Management ..........................................................................................................................6-1
6.1 Aerobic Digestion with Decant Thickening ............................................................................6-1
6.2 Anaerobic Digestion with Biogas Use ....................................................................................6-1
6.3 Dewatering ..............................................................................................................................6-2
6.3.1 Centrifuge Dewatering .............................................................................................6-2
6.3.2 Screw Press Dewatering ..........................................................................................6-3
6.4 Disposal ...................................................................................................................................6-3
7. Project Alternatives Evaluations .......................................................................................................7-1
7.1 Project Alternative Descriptions .............................................................................................7-1
7.1.1 Project Alternative 1: Activated Sludge with Anoxic Zone Package Plants ...........7-1
7.1.2 Project Alternative 2: MBR Package Plants ............................................................7-3
7.1.3 Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter ..............................7-4
7.2 Cost Evaluations .....................................................................................................................7-5
7.2.1 Capital Costs .............................................................................................................7-5
7.2.2 Operation and Maintenance Costs ..........................................................................7-6
7.2.3 Life-Cycle Costs .........................................................................................................7-6
Naalehu WWTP Revised PER Table of Contents
v
7.3 Non-Economic Evaluation ......................................................................................................7-8
7.3.1 Approach ...................................................................................................................7-8
7.4 Non-Economic Evaluation Criteria .........................................................................................7-9
7.5 Non-Economic Evaluation Results ...................................................................................... 7-10
7.6 Conclusions and Recommendation .................................................................................... 7-11
8. Preliminary Design of Improvements ...............................................................................................8-1
8.1 Site Plan ..................................................................................................................................8-1
8.2 Process Schematic .................................................................................................................8-1
8.3 Preliminary Design Criteria .....................................................................................................8-4
8.4 Preliminary Floor Plan.............................................................................................................8-6
9. Implementation Plan .........................................................................................................................9-1
9.1 Implementation Approach ......................................................................................................9-1
9.1.1 Design Bid Build Approach ......................................................................................9-1
9.1.2 Design Build Approach .............................................................................................9-1
9.2 Implementation Schedules ....................................................................................................9-2
9.2.1 Recent Change in State of Hawaii Land Use Commission Policy ..........................9-2
9.2.2 Equipment Procurement Time to Impact Construction Schedule .........................9-2
9.2.3 Implementation Schedules ......................................................................................9-2
9.3 Recommendation ...................................................................................................................9-2
10. References ..................................................................................................................................... 10-1
Appendix A: Cost Estimates ......................................................................................................................... A
Appendix B: Letter to Support Department of Hawaii Flow Variance Application .................................... B
Appendix C: Non-Economic Evaluation ....................................................................................................... C
Appendix D: Naalehu Wastewater Collection System Improvements Technical Memorandum ............. D
Naalehu WWTP Revised PER Table of Contents
vi
List of Figures
Figure 1-1. Existing Naalehu Wastewater System ..................................................................................1-3
Figure 2-1. Naalehu WWTP Service Area .................................................................................................2-2
Figure 2-2. Naalehu Phase 1 Collection System Layout ........................................................................2-4
Figure 2-3. Naalehu Phase 2 Collection System Layout–Former Brewer Company House Lots .........2-5
Figure 2-4. Life-Cycle Cost Comparison of Collection System Alternatives ...........................................2-7
Figure 4-1. Irrigation Demand Assessment .............................................................................................4-2
Figure 4-2. Subsurface Drip Irrigation Concept ......................................................................................4-3
Figure 5-1. In-Channel Cylindrical Screen ...............................................................................................5-2
Figure 5-2. Sloped Bottom Vortex Grit Removal Cross Section .............................................................5-3
Figure 5-3. Flat Bottom PISTA® Grit Removal ..........................................................................................5-3
Figure 5-4. Aerated Grit Removal Schematic ..........................................................................................5-4
Figure 5-5. HeadCell Process Schematic ................................................................................................5-5
Figure 5-6. Biotrickling Filter ....................................................................................................................5-7
Figure 5-7. Activated Carbon Scrubber....................................................................................................5-8
Figure 5-8. Membrane Bioreactor Illustration .........................................................................................5-9
Figure 5-9. Membrane Cassettes at Johns Creek Environmental Campus ....................................... 5-10
Figure 5-10. Nereda Process ................................................................................................................ 5-11
Figure 5-11. Typical Oxidation Ditch Schematic .................................................................................. 5-12
Figure 5-12. Extended Aeration Process Schematic ........................................................................... 5-12
Figure 5-13. Activated Sludge with Anoxic Selector Process Schematic............................................ 5-13
Figure 5-14. Recirculating Gravel Filter for Treatment of Septic Tank Effluent ................................. 5-14
Figure 5-15. Schematic Diagram of an On-site NaOCl Generator ...................................................... 5-17
Figure 5-16. Typical Calcium Hypochlorite Feed System .................................................................... 5-18
Figure 6-1. Centrifuge Dewatering ...........................................................................................................6-2
Figure 6-2. Screw Press Diagram .............................................................................................................6-3
Figure 7-1. Project Alternative 1: Activated Sludge with Anoxic Zone Package Plants ........................7-2
Figure 7-2. Project Alternative 2: MBR Package Plants .........................................................................7-3
Figure 7-3. Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter ...........................................7-4
Figure 7-4. Life-Cycle Cost Evaluation Results ........................................................................................7-8
Figure 7-5. Combined Economic and Non-Economic Results ............................................................. 7-11
Figure 8-1. Overall Site Plan .....................................................................................................................8-2
Figure 8-2. Process Schematic ................................................................................................................8-3
Figure 8-3. Operations Building Preliminary Floor Plan ..........................................................................8-7
Figure 9-1. Implementation Schedules ...................................................................................................9-3
Naalehu WWTP Revised PER Table of Contents
vii
List of Tables
Table 2-1. Naalehu WWTP Service Area Summary .................................................................................2-2
Table 2-2. Collection System Alternatives Cost Summary......................................................................2-6
Table 2-3. Collection System Alternatives Capital Cost Estimating Assumptions ................................2-6
Table 2-4. Life-Cycle Economic Assumptions ..........................................................................................2-7
Table 3-1. Naalehu WWTP Flows Based on 2017 CCH Standards ........................................................3-1
Table 3-2. Naalehu WWTP Calculated Flow Capacity .............................................................................3-2
Table 3-3. Recommended WWTP Capacity .............................................................................................3-3
Table 3-4. Summary of Assumed Influent Characteristics .....................................................................3-3
Table 3-5. Projected Peak Dry Weather Day Influent Mass Loads ........................................................3-4
Table 4-1. Nutrient Water Quality Standards for Class AA Embayments ..............................................4-1
Table 4-2. Relative Risk of Being Functional Equivalent to Direct Discharge .......................................4-7
Table 4-3. Recommended Subsurface Drip Disposal Design Criteria ...................................................4-8
Table 4-4. Applicable HAR 11-62 Land Disposal Requirements ...........................................................4-8
Table 5-1. Induced Vortex–Advantages and Disadvantages .................................................................5-4
Table 5-2. Aerated Grit Removal–Advantages and Disadvantages .......................................................5-5
Table 5-3. Lamella Plate Settling/HeadCell–Advantages and Disadvantages .....................................5-6
Table 5-4. Grit Capture Size Comparison ................................................................................................5-6
Table 5-5. Screening of Secondary Treatment Options ....................................................................... 5-15
Table 5-6. Bulk Sodium Hypochlorite–Advantages and Disadvantages ............................................ 5-16
Table 5-7. Onsite Sodium Hypochlorite Generation–Advantages and Disadvantages ..................... 5-17
Table 5-8. Calcium Hypochlorite Summary .......................................................................................... 5-18
Table 5-9. Chlorine Demand ................................................................................................................. 5-19
Table 5-10. UV Disinfection Design Summary ..................................................................................... 5-20
Table 5-11. Estimated Disinfection Costs ............................................................................................ 5-20
Table 7-1. Capital Cost Estimating Assumptions ....................................................................................7-5
Table 7-2. Capital Cost Estimates Summary ...........................................................................................7-5
Table 7-3. O&M Cost Assumptions ..........................................................................................................7-6
Table 7-4. O&M Cost Estimate Summary ................................................................................................7-6
Table 7-5. Life-Cycle Economic Assumptions ..........................................................................................7-7
Table 7-6. Life-Cycle Cost Analysis Summary ..........................................................................................7-7
Table 7-7. Non-Economic Comparison Criteria .......................................................................................7-9
Table 7-8. Non-Economic Comparison Criteria Weighting Factors ..................................................... 7-10
Table 7-9. Non-Economic Weighted Scores ......................................................................................... 7-10
Table 8-1. Preliminary Design Criteria .....................................................................................................8-4
Naalehu WWTP Revised PER Table of Contents
viii
List of Abbreviations
AACE Advancement of Cost
Engineering International
AOC Administrative Order on Consent
BC Brown and Caldwell
BOD5 5-day biochemical oxygen demand
CCH City and County of Honolulu
CDP Kau Community Development Plan
CWA Clean Water Act
DB design/build
DBA District Boundary Amendment
DBB design/bid/build
DNA deoxyribonucleic acid
DOH Hawaii Department of Health
ELLF end-of-lamp-life
FAI Fukunaga & Associates, Inc.
ft2 square feet
ft3 cubic feet
GAC granular activated carbon
gpcd gallons per capita per day
gpd gallons per day
gpm gallons per minute
H2S hydrogen sulfide
HAC Hawaiian Agriculture Company
HAR Hawaii Administrative Rules
I/I Infiltration and inflow
L Liter
lbs pounds
LCCs large capacity cesspools
LPHO low pressure high output
LUC Land Use Commission
MBR membrane bioreactor
Mgal million gallons
mgd million gallons per day
mL milliliter
MLSS mixed liquor suspended solids
NaOCl sodium hypochlorite
N nitrogen
NPDES National Pollutant Discharge Elimination System
NPV net present value
NRCS Natural Resources Conservation Service
O&M operation and maintenance
PER Preliminary Engineering Report
psi pounds per square inch
PWWF peak wet weather flow
RGF recirculating gravel filter
RNA ribonucleic acid
SBRs sequencing batch reactors
SES sand equivalent size
SR slow rate
SRT solids retention time
TMK tax map key
TN total nitrogen
TSS total suspended solids
UIC Underground Injection Control
USEPA United States Environmental Protection Agency
USSC United State Supreme Court
UV ultraviolet
WQS water quality standards
WWPS wastewater pump station
WWRF Wastewater Reclamation Facility
WWTP Wastewater Treatment Plant
1-1
Section 1
Introduction
This section summarizes the project background and describes key elements of the existing Naalehu
wastewater collection system.
1.1 Background
The town of Naalehu is located in the Kau district of the Island of Hawaii. According to the 2020
United States Census, the town population is approximately 1,007 persons.
The Naalehu community was established as the result of the sugar operations of the C. Brewer
Company. A portion of the community is serviced by a sewer system that was privately built, owned,
and operated by the C. Brewer Company, which merged with Hawaiian Agriculture Company (HAC) in
1972. The wastewater collected by the sewer system discharges into large capacity “gang”
cesspools (LCCs). Many years after its establishment, the private sewer system ownership was
conveyed to the County of Hawaii Department of Environmental Management.
In 1998, the U.S. Environmental Protection Agency, promulgated regulations, 40 Code of Federal
Regulations 144.14, that require the elimination of LCCs. Options to close the LCCs include
construction of a new sewer collection system located within public right-of-way and replacement of
the existing LCCs with a wastewater treatment plant (WWTP) to address the wastewater treatment
and disposal needs of the Naalehu community. These centralized WWTP options are the subject of
this Preliminary Engineering Report (PER). A separate report is being concurrently prepared that
evaluates additional options using individual wastewater systems in lieu of a new collection system
and WWTP to close the LCCs.
This report revises the 2018 PER for the Naalehu WWTP and summarizes the proposed facilities
needed to treat and dispose of wastewater flow currently discharged to the LCCs, plus additional
sewer connections. The PER presents the existing and estimated future flows and loads to the
treatment plant, describes the proposed treatment processes, recommends needed upgrades for
the WWTP to meet the future treatment levels, and provides an initial opinion of the cost to
construct, operate, and maintain the improvements project.
1.2 Existing System
The existing collection system is a network of gravity sewers that discharge to three existing LCCs.
Figure 1-1 shows the existing Naalehu wastewater collection system and service areas for the LCCs.
The LCCs in Naalehu are numbered 3, 4, and 5; LCCs 1 and 2 are located in the nearby town of
Pahala. A detailed analysis of the existing wastewater collection system was completed by others
(M&E Pacific, December 2004). The report concluded that the Naalehu community existing sewer
system consists of approximately 5,288 linear feet of 6-inch-diameter and 15,500 linear feet of
4-inch-diameter pipelines. Residential laterals connect to 4-inch sewers that discharge into 6-inch
sewer mains, predominately found in easements on private property, which transmit wastewater to
the three LCCs. There are approximately eight manholes in the sewer system. More recently
available information notes the size of piping to be between 3 and 8 inches with a few additional
sewer manholes (Fukunaga and Associates, Inc., June 2013). There are no pump stations, and the
system is not designed to collect stormwater.
Naalehu WWTP Revised PER Section 1
1-2
1.3 Report Contents
The remainder of the revised PER is organized as follows:
· Section 2 describes the service area and collection system options.
· Section 3 describes flow and load projections for the new Naalehu WWTP.
· Section 4 evaluates potential options for effluent management and details the treatment
requirements for the preferred option.
· Section 5 describes the evaluations conducted in support of the preliminary design of the
Naalehu WWTP.
· Section 6 summarizes the solids management approach.
· Section 7 describes alternative treatment options under consideration.
· Section 8 provides a preliminary design for the proposed improvements.
· Section 9 presents the proposed implementation plan for the new WWTP.
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2-1
Section 2
Collection System
This section summarizes the existing and new collection system options for the Naalehu service area
(LCC Closure Project compliance area), which was investigated by Fukunaga and Associates, Inc.
(FAI) in May 2020 in efforts to close the existing large-capacity cesspools (LCCs). The figures and
collection system layouts included within this section are reproduced from the 2020 FAI report,
which was prepared in accordance with the original 2017 AOC. Should a new WWTP be the
preferred option for implementation, an update to the collection system layout is anticipated to
finalize the service area in accordance with the 2022 Revised AOC. FAI’s Naalehu report is provided
in Appendix D.
2.1 Service Area
A concrete flood canal divides Naalehu into East (Hilo) and West (Kona) sides. The majority of the
Hilo side properties are residential, while majority of Kona side properties are commercial. Within the
town of Naalehu, there is an existing wastewater collection system that services approximately
164 former C. Brewer Company (Brewer Company) house lots on the mauka (mountain) side of
Mamalahoa Highway. The collection system is currently located within easements in private
properties and is discharged to three LCCs.
The Kau Community Development Plan (CDP) indicates the sewer system may eventually be
expanded to service the entire community; however, the collection system and wastewater treatment
plant (WWTP) presented in this report will service the former Brewer Company properties currently
connected to the LCCs and properties adjacent to the new collection system, including three
properties requesting connection. Therefore, the proposed service area constitutes the LCC Closure
Project compliance area.
Figure 2-1 shows the service area for the new WWTP, including the newly accessible properties.
Naalehu WWTP Revised PER Section 2
2-2
Figure 2-1. Naalehu WWTP Service Area
Table 2-1 provides a summary of the WWTP service area (LCC Closure Project compliance area)
property types.
Table 2-1. Naalehu WWTP Service Area Summary
Property Type Number of Parcels
Existing C Brewer Newly Accessible Total
Residential 159 25 184
Commercial 2 7 9
Church 1 1 2
Industrial - 2 2
Agricultural 1 2 3
Residential/Commercial 1 1 2
Residential/Agricultural - 1 1
Park - 1 1
Total 164 40 204
Note: Service area = LCC Closure Project compliance area
Naalehu WWTP Revised PER Section 2
2-3
2.2 Existing Collection System
In 2004, Brewer Company contracted M&E Pacific to perform a sewer system evaluation for the town
of Naalehu. The results of this investigation determined that the existing sewer lines and manholes
do not conform to the County sewer design standards. The existing sewer system was not
constructed in the streets, but instead runs through easements located on private properties, with
many collection lines running adjacent to or beneath the houses. The results of a smoke test
performed during the 2004 sewer system evaluation identified at least 13 locations of line breaks
and/or pipe defects and 12 household units with defective sewer vents. In addition, the existing
sewer system is over 80 years old, long surpassing its expected lifespan, and will require extensive
repair and rehabilitation if chosen to be reused.
The recommended alternative, which received overwhelming support from Naalehu voters in 2004,
consists of constructing a new sewer system in the streets to meet the County sewer standards and
to allow the collection system to be owned and operated by the County (M&E Pacific, December
2004).
Nearly 20 years have passed since the 2004 study was completed. In order to reuse the existing
collection system into the future an updated condition assessment study is recommended to better
identify system deficiencies. Substantial improvements will likely be necessary due to the age of the
system. Reusing the existing collection system will require constructing the Phase 1 collection
system scenario described below to connect to the proposed WWTP and close the LCCs.
2.3 Phase 1 Collection System Project
In efforts to close the existing LCCs, FAI conducted a collection system investigation in May 2020.
The investigation recommends a two-phase approach. Phase 1 involves utilizing the existing
collection system within the Brewer Company house lots and constructing new gravity sewers,
wastewater pump station, and force main to transport sewage from the LCCs to the new WWTP.
Phase 1 consists of the following:
1. Construct a new gravity sewer on Kaalaiki Road and Naalehu Spur Road to the WWTP located on
a portion of Tax Map Key (TMK) (3) 9-5-007:016.
2. Construct a new pump station located on a portion of TMK (3) 9-5-008:048, and construct a new
force main, which crosses an existing storm drainage channel at Melia Street, to connect to the
Kaalaiki Road gravity sewer.
3. Construct a new gravity sewer on Opukea Street and Ohai Road to intercept existing flows
entering the LCCs and divert sewage to the wastewater pump station (WWPS) and transport
flows to the gravity sewer along Kaalaiki Road.
Figure 2-2 illustrates the transmission system layout established by FAI in May 2020 for the Phase 1
collection system.
Naalehu WWTP Revised PER Section 2
2-4
Figure 2-2. Naalehu Phase 1 Collection System Layout
Naalehu WWTP Revised PER Section 2
2-5
2.4 Phase 2 Collection System Project
The Phase 2 collection system project consists of the installation of gravity sewers within the streets
to replace the existing collection system. Figure 2-3 shows the former Brewer Company housing area
Phase 2 collection system established by FAI in May 2020.
Figure 2-3. Naalehu Phase 2 Collection System Layout–Former Brewer Company House Lots
2.5 Collection System Alternatives
Two collection system alternatives were evaluated for Naalehu:
· Phase 1 Only: Reuse Existing Collection System: This alternative would construct the Phase 1
project to close the LCCs. The existing collection system would continue to be used.
· Phase 1+2: All New Collection System: This alternative would construct both Phase 1 and
Phase 2 to create an all-new collection system for the community.
Naalehu WWTP Revised PER Section 2
2-6
2.6 Collection System Costs
Table 2-2 summarizes the capital, operation and maintenance (O&M), equipment replacement, and
life-cycle costs for the two collection system alternatives. The capital costs were calculated by FAI in
their Naalehu Wastewater Collection System Improvements Technical Memorandum (Appendix D)
conducted in May 2020, adjusted to current (June 2023) dollars.
Phase 1 capital costs include an additional $4.4 million from FAI’s estimate to account for capital
costs related to reusing the existing collection system, such as inspection, cleaning, and repairing of
existing defects. Both scenarios include an estimated $400,000 WWPS equipment replacement cost
after 20 years. The life-cycle costs consist of the 30-year net present value (NPV) of the capital, O&M,
and 20-year equipment replacement costs. Additional detail is included in Appendix A.
Table 2-2. Collection System Alternatives Cost Summary
Collection System Alternative Capital
Cost ($M)
Annual O&M
Cost ($/year)
WWPS Equipment Replacement
(20-yr)
Life-Cycle Cost
($M)
Phase 1 Only: Reuse Existing Collection System $30.0 $240,000 $400,000 $35.9
Phase 1+ Phase 2: All New Collection System $40.2 $74,000 $400,000 $42.2
Table 2-3 provides a summary of capital cost assumptions used for the collection system cost
analysis.
Table 2-3. Collection System Alternatives Capital Cost Estimating Assumptions
Description Value
Estimate date June 2023
Engineering News Record 20-Cities Average Construction Cost Index 13,345
Engineering, administration, and legal markup 25 percent
Estimating contingency for unknowns 20 percent
The life-cycle cost evaluation consists of a NPV comparison of the two alternatives. The NPV analysis
includes capital, annual O&M, and periodic equipment replacement costs. The capital expenditure is
assumed to occur in year 1, and annual O&M costs are incurred during years 2 through 30. A pump
station equipment replacement project is assumed to occur in year 20. An appropriate inflationary
factor and discount rate are applied to the cash flow projections to obtain the NPV over a 30-year
planning period.
The NPV of an alternative represents the amount of money that would need to be set aside today (at
a given interest rate) to pay the costs associated with the alternative over the entire planning period.
The alternative with the lowest NPV is considered the most attractive from an economic perspective.
Naalehu WWTP Revised PER Section 2
2-7
Table 2-4 summarizes the life-cycle cost evaluation assumptions.
Table 2-4. Life-Cycle Economic Assumptions
Description Value
Year of analysis 2023
Planning period 30 years
Inflation rate 3.5 percent
Discount rate 5.0 percent
Equipment replacement cycle 20 years
The life-cycle costs are shown graphically on Figure 2-4. Reusing the existing Brewer Company
collection system has the lowest capital and life-cycle costs.
Figure 2-4. Life-Cycle Cost Comparison of Collection System Alternatives
$30,032,500
$40,165,000
$5,898,000
$2,033,000
$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
$40,000,000
$45,000,000
Phase 1 Only: Reuse Existing
Collection System
Phase 1 + Phase 2: All New
Collection SystemLife-cycle Cost (30-year NPV)Capital Cost O&M Cost
Naalehu WWTP Revised PER Section 2
2-8
2.7 Recommendation
Although reusing the existing collection system appears to incur lower life-cycle costs than
constructing an all-new collection system, it is not recommended. Due to the advanced age of the
existing collection system, the option would incur substantial financial, public health, and
environmental risks to the County, as summarized below:
· The piping is at the end of its useful service life; catastrophic failures are likely to increase in
frequency, resulting in greater risks to public health and the environment.
· Most of the system is located in backyard easements, making it difficult to access and maintain.
· System expansion to accommodate sewering additional areas of the town (in accordance with
the Kau CDP) would not be feasible.
· The option does not address the Administrative Order on Consent requirement to connect
additional properties that are currently not connected to the collection system to the WWTP.
A new conventional gravity sewer collection system constructed in the streets of the Brewer
Company lot development (Phase 2) is a viable solution to meet the wastewater collection needs of
the town of Naalehu. From a technical perspective, the Phase 1 + Phase 2 option is recommended
for implementation should a new WWTP be constructed. It is anticipated that additional non-
technical considerations such as financing options, community input, burden on the Naalehu
community, and detailed alignment with County long term planning goals will be addressed outside
of this preliminary engineering report.
The County provided the following statement:
“COH will continue working with, planning department, community leaders, and developers for long
term accomplishments of the CDP as this will take more time and effort than what was given within
the AOC. Better planning decisions can be made as the COH can continue monitoring growth, work
with planning department on the general plan 2045, finalize the cesspool conversion master plans,
and be able to negotiate a better financial plan with all stakeholders aka developers, businesses,
state government agencies, and the community at large.”
3-1
Section 3
Flow and Load Projections
This section summarizes the wastewater flow and load projections for the new Naalehu wastewater
treatment plant (WWTP).
3.1 Flow Projections Based on City and County of Honolulu
Standards
Section 11-62-24(b) of the Hawaii Administrative Rules (HAR) requires Counties to use their adopted
wastewater flow standards to develop flow projections for WWTPs. Counties are to use the City and
County of Honolulu (CCH) flow standards if they have not adopted their own standards. The County of
Hawaii has not adopted its own flow standards, so wastewater flow projections were developed using
current CCH wastewater standards (2017). Table 3-1 summarizes the flow projections.
Table 3-1. Naalehu WWTP Flows Based on 2017 CCH Standards
Description Value (gallons per day) Peaking Factor
Average dry weather flow 225,000 1.0
Peak day dry weather flow 446,000 2.0
Peak day wet weather flow a 563,000 2.5
Peak hour wet weather flow 480 gallons per minute
(691,000 gallons per day) 3.1
a. Peak day wet weather flow is not part of the CCH standards but is an important WWTP design parameter.
Peak day wet weather flow estimate was developed using an appropriate peaking factor.
The CCH standards were established for a major metropolitan area that includes vast areas of
residential, commercial, and industrial development, with significant proportions of service areas
near sea level elevations. Wastewater generation rates are generally lower in rural areas than in
urban areas. The County’s experience with the CCH flow standards on other projects (e.g., Honokaa
WWTP) has illustrated that the standards are very conservative for small rural communities located
at higher elevations on Hawaii Island. Therefore, the current wastewater standards based on urban
Honolulu are likely overly conservative for rural communities like Naalehu.
3.2 Reduced Flows Based on Potable Water Records
The amount of wastewater generated within a residence will not exceed the amount of potable water
used by the occupants. Therefore, potable water use records can be used to estimate wastewater
generation rates within existing communities where no combined sewers are present. The County of
Hawaii Department of Water Supply provided potable water use records for the parcels located
within the service area from November 2017 through October 2022. Evaluation of the potable water
use data is discussed in Appendix B. Analysis of the potable water use records indicates that an
80,000 gallons per day (gpd) monthly wastewater generation rate would reflect the current needs of
Naalehu WWTP Revised PER Section 3
3-2
the service area. Using a 2.5 peaking factor to estimate the maximum wastewater flow into the
collection system results in a maximum wastewater flow of 200,000 gpd.
3.2.1 Dry Weather I/I Allowance
Groundwater can infiltrate into wastewater collection systems during dry weather, increasing flows to
the WWTP. The 2017 CCH standards specify a dry weather infiltration and inflow (I/I) allowance of
35 gallons per capita per day (gpcd). The previous CCH standards (dated 1993) specified a dry
weather I/I allowance of 5 gpcd for properties located above the groundwater table. Through the
County’s experience at Honokaa evaluating dry weather I/I for a rural collection system located in
Hawaii Island’s well-drained geology, at elevations hundreds of feet above sea level and a significant
distance from the shoreline, we conclude that continued use of the 1993 standard for dry weather
I/I is appropriate for Naalehu and using the 2017 standard would be overly-conservative. Further
discussion is provided in Appendix B.
3.2.2 Wet Weather I/I Allowance
The 2017 CCH standards, which specify a wet weather I/I allowance of 3,000 gallons per acre per
day, were used for all wet weather I/I calculations.
3.2.3 Reduced Flow Projections
Accurately quantifying flow projections for the Naalehu community is necessary to design an
appropriately sized wastewater treatment and disposal facility. The WWTP design will provide
sufficient capacity for the existing parcels within the service area, including newly accessible parcels,
reflecting current development. This will allow the County to close the three LCCs. Furthermore, the
design will provide sufficient area within the WWTP site for future expansion. Table 3-2 provides a
summary of the calculated WWTP capacities for the reduced flow projections and for the flow
projections for future development based on the 2017 CCH Standards.
Table 3-2. Naalehu WWTP Calculated Flow Capacity
Description Reduced Flow Projections Flow Projections Based on 2017 CCH Standards
Base sanitary flow 80,000 gpd 147,000 gpd
Peak hour sanitary flow 200,000 gpd 368,000 gpd
Dry weather I/I 12,000 gpd 78,000 gpd
Wet weather I/I 245,000 gpd 245,000 gpd
Average dry weather flow 92,000 gpd 225,000 gpd
Peak day dry weather flow 212,000 gpd 446,000 gpd
Peak day wet weather flow 322,000 gpd
Peaking Factor = 3.5
563,000 gpd
Peaking Factor = 2.5
Peak hour wet weather flow 317 gpm (457,000 gpd) 480 gpm (691,000 gpd)
HAR 11-62-23.1(i) requires the initiation of a facility planning process when the actual wastewater
flows (measured at the WWTP) reach 75 percent of the design capacity of the WWTP, and
implementation of the facility plan must be initiated when actual wastewater flows (measured at the
WWTP) reach 90 percent of the design capacity. In anticipation of future development, we
recommend the WWTP design be rated to treat an average dry weather flow of 125,000 gpd to avoid
the potential of having to initiate a facility plan shortly after the project is constructed. Note that the
Naalehu WWTP Revised PER Section 3
3-3
biological processes in the mechanical WWTP will need to be sized to treat the peak day dry weather
flow of 212,000 gpd, not the average dry weather flow.
The proposed WWTP design capacity is based on actual water use data to establish wastewater
generation rates, and rational assumptions to establish dry weather I/I allowances, and we believe it
is appropriate for the existing conditions, while providing limited capacity for growth. Table 3-3
presents the recommended design capacity for the reduced flow projections.
Table 3-3. Recommended WWTP Capacity
Description Value Peaking Factor
Average dry weather flow 125,000 gpd 1.0
Peak day dry weather flow 212,000 gpd 1.7
Peak day wet weather flow 322,000 gpd 2.6
Peak hour wet weather flow 457,000 gpd (317 gpm) 3.7
3.2.4 Flow Variance
If the County pursues a WWTP approach (using the recommended capacity in Table 3-3) to close the
LCCs then a DOH variance from HAR 11-62 requirements will be needed. The variance will need to
be renewed every 5 years. The WWTP capacity needs should be re-evaluated upon application for the
variance renewal.
3.3 Influent Characteristics
The properties within the existing service area are primarily residential, but do include several
commercial, agricultural, and industrial zoned parcels. The wastewater characteristics of the WWTP
influent are assumed to be similar to typical domestic wastewater. Table 3-4 provides a summary of
the assumed influent characteristics.
Table 3-4. Summary of Assumed Influent Characteristics
Parameter Value (mg/L)
5-day biochemical oxygen demand (BOD5) 300
Total suspended solids (TSS) 300
Total nitrogen 40
Total phosphorus 7
3.4 Influent Mass Loads
Table 3-5 summarizes the projected loads to the WWTP, based on the proposed peak day dry
weather capacity of 212,000 gpd and the influent characteristics presented above.
Naalehu WWTP Revised PER Section 3
3-4
Table 3-5. Projected Peak Dry Weather Day Influent Mass Loads
Description Value (lbs/day)
BOD5 530
TSS 530
Total nitrogen 71
Total phosphorus 12
4-1
Section 4
Effluent Management Alternatives
and Regulatory Requirements
Effluent management alternatives are evaluated in this section, followed by an assessment of
regulatory requirements for the recommended effluent management system.
4.1 Effluent Management Alternatives
Effluent management alternatives are evaluated below.
4.1.1 Ocean Discharge
Ocean discharge of treated effluent is not considered a viable alternative for this small community
due to the long distance to the shoreline (approximately 2 miles), high cost to construct an outfall,
stringent receiving water quality standards, high receiving water monitoring cost, and difficulty and
length of time required to secure the required permits. The coastal waters in the Naalehu area are
classified as “AA” marine waters by State of Hawaii Department of Health (DOH). Hawaii
Administrative Rules (HAR) 11-54 does not allow zones of mixing in waters up to a distance of
300 meters (1,000 feet) offshore if there is no defined reef area and if the depth is greater than
18 meters (10 fathoms). The water quality criteria for nutrients for Class AA embayments are listed
in Table 4-1. If a mixing zone is not provided, then a WWTP discharging to the coastal waters would
be required to treat water to meet the applicable water quality criteria. Treatment to the specified
levels is not feasible with current technologies. Therefore, ocean discharge is not feasible without a
mixing zone and an outfall at least 1,000 feet offshore would be required for Naalehu.
Table 4-1. Nutrient Water Quality Standards for Class AA Embayments
Parameter Geometric mean not to
exceed (µg/L)
Not to exceed the given value more
than 10% of the time (µg/L)
Not to exceed the given value more
than 2% of the time (µg/L)
Total nitrogen 200 350 500
Ammonia nitrogen 6 13 20
Nitrate + nitrate nitrogen 8 20 35
Total phosphorus 25 50 75
4.1.2 Subsurface Disposal via Injection Wells
Per HAR, Title 11, Chapter 23, disposal to groundwater via an injection well is not allowed mauka of
the DOH Underground Injection Control (UIC) line. The UIC line in the Naalehu area is located along
the shoreline. Since the town of Naalehu is located mauka of the UIC line, an injection well is not a
viable alternative. In addition, per Environmental Protection Act 131, DOH is prohibited from issuing
permits “for the construction of sewage wastewater injection wells unless alternative wastewater
disposal options are not available, feasible or practical”. Therefore, subsurface disposal via injection
wells is not feasible.
Naalehu WWTP Revised PER Section 4
4-2
4.1.3 Water Recycling
This section summarizes Brown and Caldwell’s (BC’s) evaluation of water recycling as the primary
effluent management system.
4.1.3.1 Irrigation
An irrigation assessment was completed to determine the viability of water recycling as the primary
effluent management system, assuming the recycled water would be used to irrigate nearby coffee
trees or other agricultural crops.
Figure 4-1 presents a summary of the assessment, which shows there is typically no irrigation demand
for 3 months of the year (November through January) due to high rainfall. In addition, the DOH requires
that all water recycling programs have a 100 percent backup disposal system in place to handle flow
that does not meet recycled water quality standards or when recycled water supply exceeds demand.
Therefore, water recycling is not a viable primary or sole effluent management strategy for the
community at this time. However, water recycling treatment, storage, and distribution systems could be
added in the future. In addition to nearby irrigated agricultural reuse, the Naalehu Park and Naalehu
Elementary School have significant areas of turf that could be considered for future irrigation with
recycled water that meets the DOH “R-1” standards.
Figure 4-1. Irrigation Demand Assessment
4.1.3.2 Stock Water
The proposed WWTP site is located on a large ranch parcel. The County evaluated recycled water for
stock watering purposes in November 2019 (BC, November 2019). The study concluded that
recycled water that meets DOH R-1 standards could be used for stock watering purposes. The
estimated peak stock water demand was 29,000 gallons per day (gpd), approximately 23 percent of
the proposed average dry weather flow capacity of the WWTP. Stock water use appears to be
feasible if a water recycling program is developed in the future.
0
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JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Irrigation Demand (gal/ac-day)Precipitation and Evapotranspiration (in)Precipitation Evapotranspiration Irrigation Demand
Naalehu WWTP Revised PER Section 4
4-3
4.1.4 Slow Rate Land Treatment
A potential project effluent management concept consists of Type 1 slow rate (SR) land treatment,
which involves irrigation of vegetation with effluent. Type 1 slow rate land treatment differs from
water recycling in that it is a disposal method, and effluent is typically applied in excess of the
irrigation needs of the vegetation. The potential effluent management concept calls for grading the
site to contain all precipitation and planting native Hawaiian trees within the effluent disposal area.
Effluent would be applied using surface (flood) irrigation techniques.
The soils at the proposed WWTP location are suitable for SR land treatment. The proposed WWTP
effluent management system will make use of an area containing Naalehu medial silty clay loam soil
(Natural Resources Conservation Service [NRCS], 2018). This soil type is well drained with
moderately high to high permeability. SR land treatment consists of irrigation of land and vegetation
with effluent. Significant treatment is provided as the water percolates through the soil. The
vegetation uses the nutrients in the effluent as fertilizer and transpires a portion of the applied
water. SR land treatment serves as a means for final disposal of effluent.
4.1.5 Subsurface Drip Irrigation Disposal
Another effluent management concept is to retain the existing site topography along with the existing
vegetation and use subsurface drip irrigation technology to apply the effluent within the effluent
disposal area. The use of subsurface drip irrigation technology to disperse effluent at the site will
allow the County to significantly reduce the amount of clearing, grubbing, and grading required to
construct the facility, as compared to slow rate land treatment.
Drip irrigation technology has evolved to the point where non-clog emitters are available for
subsurface applications of effluent. Non-clog subsurface emitters decrease the potential for the
irrigation components to be clogged by roots.
Figure 4-2 illustrates the subsurface drip concept. Drip tubing with integral emitters is buried 6 to
9 inches below ground. Effluent emitters are typically designed to operate at a flow rate of 1 gallon
per hour (gph) and are typically spaced every 2 feet along a drip line. Pressure compensating drip
systems typically operate under pressures ranging from 10 to 45 pounds per square inch (psi).
Figure 4-2. Subsurface Drip Irrigation Concept
(Courtesy of Geoflow, Inc.)
Naalehu WWTP Revised PER Section 4
4-4
Subsurface drip irrigation technology incurs greater operation and maintenance than a surface
irrigation system. The County would need to periodically flush the drip lines to remove debris. As
described below, a significant number of drip lines are necessary to accommodate peak flow rates.
In addition, periodic chlorination would be required to remove biological growth from the drip lines.
These O&M tasks would need to be completed on a regular schedule, because drip systems are
buried and not readily accessible or observable. During periods of dry soil conditions, the County
would need to inspect the disposal area for patches of wet soil that would indicate a localized failure
that requires repair. Flow and pressure monitoring would also be useful tools for validating the status
of the subsurface drip system. The disposal area would be divided into multiple irrigation zones,
allowing a zone to be taken out of service for maintenance purposes. A fence would be constructed
around the site to deter entry by humans and ungulates.
The subsurface drip system would slowly disperse effluent 6 to 9 inches below the ground surface,
therefore operating as a subsurface disposal system similar to a leach field. Effluent is not intended
to surface with a properly operating subsurface drip system. Precipitation falling on the site would
either percolate into the soil or run off as surface drainage. The amount of runoff from the site would
vary with the storm intensity; precipitation rates in excess of the infiltrative capacity of the site soils
would result in runoff. The implementation of a subsurface disposal system will allow the existing
grading to be retained, because stormwater runoff will not come into contact with, and therefore will
not contain, effluent.
4.1.6 Leach Field
A leach field could potentially be constructed for subsurface disposal of treated effluent. Preliminary
assessment of the concept based on the site soil characteristics (NRCS, 2018) and HAR 11-62
indicate approximately 14 acres of leach fields would be required to accommodate the anticipated
flow, which includes a 100-percent redundant drain field per the DOH requirements. There is
insufficient soil area available at the proposed WWTP site to construct a leach field of this size;
therefore, this alternative is considered to be not feasible.
4.1.7 Ramifications of United States Supreme Court Opinion on County of Maui,
Hawaii v. Hawaii Wildlife Fund et. al.
The United States Supreme Court (USSC) has published its opinion on the case of Hawaii Wildlife
Fund, et al. vs. County of Maui regarding whether the injection wells at the Lahaina Wastewater
Reclamation Facility (WWRF) are subject to regulation under the Clean Water Act (CWA) National
Pollutant Discharge Elimination System (NPDES) program. The USSC ruled that a discharge of
pollutants that originate from a point source but are conveyed to navigable waters by a nonpoint
source (in the Lahaina situation, groundwater) are subject to regulation under the NPDES program if
the nonpoint source is a “functional equivalent” of a point source discharge. Unfortunately, the term
“functional equivalent” is not well defined at this time. The USSC decision offered two examples of
what would and would not be considered functional equivalents to a direct discharge:
· A pipe ending a few feet from a navigable water and the pipe emits pollutants that travel those
few feet through groundwater (or over the beach) to the navigable water would clearly be subject
to NPDES regulation.
· If a pipe ends 50 miles from navigable waters and the pipe emits pollutants that travel with
groundwater, mix with much other material, and end up in navigable waters only many years
later, would not be subject to NPDES regulation.
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The two examples represent the two extreme situations. The USSC also offered some vague
guidance as to how situations between the two extremes could be handled. Specifically, seven
relevant factors were listed that could be applied to specific situations:
1. Transit time.
2. Distance travelled.
3. The nature of the material through which the pollutant travels.
4. The extent to which the pollutant is diluted or chemically changed as it travels.
5. The amount of pollutant entering the navigable waters relative to the amount of the pollutant
that leaves the point source.
6. The manner by or area in which the pollutant enters the navigable waters.
7. The degree to which the pollution (at that point) has maintained its specific identity.
The USSC opinion further states that “time and distance will be the most important factors in most
cases, but not necessarily every case”. The USSC was not able to provide additional guidance as to
what would constitute a functional equivalent to a direct discharge, leaving substantial regulatory
uncertainty that requires resolution.
4.1.7.1 The Road to Regulatory Clarity
Regulatory clarity is important to public agencies tasked with protecting public health and the
environment by managing wastewater from communities. Environmental protection projects are
often costly, and it is important for public agencies to have a level of confidence that a project will
meet regulatory requirements over the project lifecycle before public funds are expended.
Unfortunately, the USSC opinion does not provide regulatory clarity. There are four potential ways
that regulatory clarity can be achieved:
1. Regulatory guidance documents: The U.S. Environmental Protection Agency (USEPA) or State of
Hawaii could issue regulatory guidance documents that establish criteria for determining if a
particular discharge scenario is a functional equivalent to a direct discharge. Developing
regulatory guidance documents would be the fastest way to address the problem but would also
be the weakest approach because regulatory guidance documents aren’t subject to a public
review process and don’t carry the authority of the options listed below.
2. Regulations: The USEPA and/or State of Hawaii could develop regulations that define conditions
whereby a discharge is a functional equivalent to a direct discharge. Development of regulations
takes longer than development of regulatory guidance documents because a public participation
process is involved.
3. Legislation: The United States and/or State of Hawaii governments could enact legislation that
defines what is functionally equivalent to a direct discharge.
4. Court rulings: The definition of what it means to be a functional equivalent to a direct discharge
could be resolved via court cases. This would be the slowest pathway of the four.
Based on the above, it will likely take years to decades before the term “functional equivalent” is
adequately defined to a point where agencies have regulatory clarity.
4.1.7.2 Complications of Discharges within the State of Hawaii
The USSC opinion is especially complicated for most forms of effluent discharge in the State of
Hawaii, because of the unique hydrogeology of volcanic islands. Our islands are surrounded by the
navigable waters of the Pacific Ocean, and water that percolates into the soil that does not
evaporate or is not taken up by vegetation via evapotranspiration will eventually find its way to the
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groundwater that moves mauka to makai and into the ocean. Therefore, any pollutants that
percolate to groundwater will eventually find their way to navigable waters.
A further complication is the State of Hawaii’s water quality standards (WQS) that define ocean water
quality criteria for discharge into the ocean. These standards are an order of magnitude lower (i.e.,
more restrictive) than what can be achieved with existing advanced treatment technology. Treatment
technology is currently not available that can reliably produce effluent that meets the WQS. While
technology is available that can purify wastewater to where it is safe to drink (at great expense),
ironically that same purified water cannot not be discharged into the ocean in certain places or
certain conditions because it would not meet the water quality standards the State has established
for ocean waters.
4.1.7.3 United States District Court Ruling
Subsequent to the USSC decision, the U.S. District Court in Honolulu ruled the Lahaina WWRF
injection wells are functionally equivalent to a direct discharge and are subject to the CWA and
require an NPDES permit. The DOH is in the process of issuing an NPDES permit to the facility. The
U.S. District Court Ruling establishes another data point in addition to the two provided by the USSC
regarding whether a discharge is functionally equivalent to a direct discharge:
· The transit time from the Lahaina WWRF injection wells to the Pacific Ocean is a minimum of
84 days, reaches peak concentration in 9 to 10 months, and continues for 3 to 5 years after
discharge to the injection wells. A dye tracer test was used to establish the transit time.
· The straight-line distance traveled from the injection wells to the Pacific Ocean is approximately
2,900 feet (0.55 miles), although the groundwater in the aquifer takes a non-linear route.
4.1.7.4 Functional Equivalent Risk
As discussed above, the USSC opinion establishes at least seven factors to be used to determine
whether an indirect discharge is a “functional equivalent” to a direct discharge, and without
regulatory action, legislative direction, or additional legal precedents, agencies that desire to
implement an indirect discharge system are placed in a position of regulatory uncertainty. The risk
can be eliminated by:
· Implementing a direct discharge system (e.g., ocean outfall) that is known to be subject to the
NPDES program.
· Implementing a true zero-discharge system, i.e., evaporation.
All other forms of disposal carry risk of being a functional equivalent to a direct discharge. Site-
specific factors need to be evaluated for each particular discharge system and location. However,
each type of discharge system provides different degrees of treatment and environmental
attenuation. Therefore, for a given site certain options present less risk than others.
Table 4-2 shows BC’s opinion of the risk of various effluent management systems that have been
discussed in relation to each other, assuming disposal systems that provide more treatment present
less risk than disposal systems that provide less treatment.
Of the indirect discharge systems, discharge to groundwater via injection wells is shown as having
the highest risk of being functionally equivalent to direct discharge because treated effluent is added
directly to the groundwater in a discrete area.
Leach fields are shown to have lower risk than injection wells because effluent is applied near the
surface over a large area and treatment occurs as the applied water percolates through the
unsaturated soil.
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Table 4-2. Relative Risk of Being Functional Equivalent to Direct Discharge
Classification Risk of Being Functional
Equivalent to Direct Discharge Effluent Disposal System
Direct discharge Not applicable Direct discharge to ocean
Indirect discharge
Highest risk
Discharge to groundwater via injection wells
Leach fields
Slow rate land treatment and subsurface drip disposal systems
Lowest risk Water recycling
Slow rate land treatment and subsurface drip disposal are shown as having lower risk because the
effluent is applied over a large area at or near the surface, and the presence of managed vegetation
allows a higher degree of treatment to occur before the water percolates to groundwater.
Water recycling in the form of irrigation carries the lowest risk because it produces the smallest
volume of deep percolate of the options shown.
4.1.7.5 Functional Equivalent Risk at Naalehu
At the current time we believe the risk of any of the feasible effluent management alternatives for
Naalehu (water recycling, slow rate land treatment, subsurface drip disposal, and leach field) being
found to be the functional equivalent to a direct discharge are low due to the following
considerations:
· The effluent management system(s) would be located at an elevation of approximately 680 feet
above sea level, creating a large vadose zone that applied effluent would need to travel down
before reaching the basal groundwater lens.
· The effluent disposal site is located nearly 2.5 miles from the shoreline, likely resulting in a long
travel time.
· The effluent flows will be relatively small at this facility, and there are no documented
groundwater quality problems in the area.
However, it must be noted that future court rulings, legal action, legislation, or regulatory actions
could render the facility to be functionally equivalent to a direct discharge and subject to NPDES
permitting requirements.
4.1.8 Recommendation
Subsurface drip irrigation system is the recommended method of effluent disposal for the Naalehu
WWTP. Subsurface drip will incur lower capital cost and require less attention from WWTP operators
with respect to vegetation maintenance than slow rate land treatment. Subsurface drip requires
periodic maintenance chlorination to eliminate biofouling in the drip lines. Recommended design
criteria for the subsurface drip irrigation system are presented in Table 4-3. The disposal system
would be sized to handle the peak day wet weather flow of 322,000 gpd. An irrigation equalization
and control tank are proposed to equalize higher peak flows and to allow discrete dosing of the
irrigation zones.
HAR 11-62 requires a fully redundant subsurface disposal system. The design criteria listed in
Table 4-3 are based on providing a subsurface drip system that is two times larger than needed in
order to satisfy the HAR 11-62 requirement for redundancy. The drip system ould be divided into two
separate systems so that the peak day wet weather flow can be disposed on the site using one
system while the second system is out of service for maintenance.
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Table 4-3. Recommended Subsurface Drip Disposal Design Criteria
Description Value
Average dry weather flow 125,000 gpd (87 gpm)
Peak day wet weather flow 322,000 gpd (224 gpm)
Irrigation equalization and control tank volume 20,000 gallons
Disposal area 5.2 acres
Subsurface drip emitters 1 gallon per hour, pressure compensating
Number of emitters needed for peak day wet weather flow 13,417 emitters
Number of systems 2 (1 active, 1 redundant)
Number of emitters provided to provide 2x redundancy 26,833 total emitters
Emitter spacing 2 feet
Drip line length per system 26,833 feet
Total drip line length 53,667 feet
Drip line spacing 4 feet
Drip line depth 6 to 9 inches
Number of irrigation zones 4 (2 per system)
Length of drip line per zone 13,417 feet
Flow per irrigation zone 112 gpm
Irrigation system monitoring Flow meter(s) and pressure indicators
During high flow conditions the irrigation control system would open multiple irrigation zones to
accommodate the disposal needs. Additional drip lines will need to be added when the WWTP
capacity is expanded. The minimum spacing between drip lines is 2 feet, so there will be sufficient
space between the initial drip lines to add additional drip lines as part of future expansion project(s).
4.2 Treatment Requirements
The DOH regulates subsurface drip irrigation disposal as “land disposal” per HAR 11-62. Table 4-4
lists the applicable effluent requirements for land disposal applicable to the project in effect at the
time this report was prepared.
Table 4-4. Applicable HAR 11-62 Land Disposal Requirements
Description Value HAR Reference
5-day biochemical oxygen demand (BOD5) 30 milligrams per Liter (mg/L) monthly average
60 mg/L peak 11-62-26
TSS 30 mg/L monthly average
60 mg/L peak 11-62-26
Disinfection Except for subsurface disposal systems, continuous disinfection of the
treated effluent shall be provided. 11-62-24
Setbacks Treatment units shall be not less than 25 feet from property lines nor less
than 10 feet from any building. 11-62-23.1
Public accessibility control 6-foot-high fence surrounding treatment units 11-62-08
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Section 5
Wastewater Treatment Evaluations
This section summarizes the evaluations conducted as part of developing the proposed wastewater
treatment plant (WWTP).
5.1 Preliminary Treatment
The preliminary treatment system will include influent flow measurement, influent sampling
equipment, screening, and grit removal.
5.1.1 Influent Flow Measurement
Influent flow measurement is recommended to allow assessment of flows and loads to the biological
treatment process, and to assess the biological treatment process performance. A Parshall flume will
be provided upstream of the screening system to continuously record influent flow rates. Parshall
flumes work well for influent measurement because the flume can operate in an open-channel
configuration, can accommodate wide ranges of flows, and is self-cleaning. A straight approach
length of at least 20 times the flume throat width will be provided upstream of the flume to provide
favorable hydraulic conditions.
5.1.2 Influent Flow Sampling
An automatic refrigerated composite sampler is recommended to allow influent composite samples
to be collected. Influent composite samples, when combined with influent flow measurement, can be
used to calculate influent mass loading rates to the WWTP to assess the treatment performance and
optimization of aeration rates in the biological treatment process. Periodic influent sampling is also
recommended to monitor for changes in the influent characteristics.
5.1.3 Screening
Screening is recommended to protect the downstream system operations from large objects, debris,
wipes, and rags that can be present in wastewater. The industry trend is towards finer screening
systems that remove greater amounts of debris from the waste stream; screens with 6-millimeter
(1/4 inch) openings are frequently used for activated sludge treatment systems. Finer screens are
used upstream of membrane bioreactors to remove hair that can foul the membranes. The
screenings volume at the Naalehu WWTP is expected to be small, subsequently screenings disposal
is expected to be infrequent; weekly at most. Therefore, the screenings must be washed of organic
debris to prevent the accumulation of nuisance odors and flies in the screenings barrel or bag
between screening disposal events.
5.1.3.1 In-Channel Cylindrical Screen
We recommend an in-channel cylindrical screen for this installation. The in-channel cylindrical screen
combines screening, screenings washing, dewatering, compacting, and bagging/disposal within a
single unit. The screening portion consists of an inclined screen basket inserted into the wastewater
channel. The screening basket can consist of bars, perforated plates or sieves, depending on the
application and clear opening required. The controls can be set to allow a mat to build up on the
screening surface, allowing finer screening of the wastewater. Controlled by head loss, a rake arm
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starts rotating within the screen basket, pushing the screenings off the rake and into a perforated
screenings hopper located at the screen’s central axis. A shafted auger along the screen axis
conveys the screenings from the hopper through an inclined tube, which dewaters and compacts the
screenings. The tube includes a perforated dewatering section. The discharged screenings are about
40-percent dry and can be discharged into a bin or directly into a bagging system.
Figure 5-1 illustrates the process. Manufacturers include Lakeside and Huber. The key benefit to this
system is the integrated screenings washing system, minimizing additional screenings handling and
odor potential. For this installation, the headworks will include one in-channel cylindrical screen, plus
a bypass channel with manually cleaned bar rack.
Figure 5-1. In-Channel Cylindrical Screen
5.1.4 Grit Removal
Grit is comprised of particles that are heavier than the organic biodegradable matter in wastewater.
Grit particles can consist of sand, gravel, pebbles, silt, cinders, ground bone, eggshells, coffee
grounds, and other materials. Grit in the wastewater collection and treatment system causes
abrasive wear to mechanical equipment, piping, and appurtenances. Grit can also form deposits in
pipelines, channels, and tanks, which reduces hydraulic capacity and can damage equipment.
Removal of grit is very important to help prevent wear to downstream equipment, costly service
interruptions and repair.
Grit removal systems usually are placed between screening and downstream treatment processes.
At this point, the largest materials have been removed by the screens and will not interfere with grit
handling equipment.
There are several types of grit removal methods, including induced vortex grit removal, aerated grit
chambers, and lamella plate settlers. The type of grit removal chosen is mainly dependent on the
size of the incoming grit particles and the desired capture rate. Removed grit must be washed,
dewatered, and disposed.
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5.1.4.1 Induced Vortex Grit Removal
Historically, vortex grit removal, or the circular grit chamber, has been the most widely used method
for grit removal in the United States, Vortex grit removal relies on the principle that grit has a greater
specific gravity than organic matter.
There are two configurations of vortex grit removal systems: a sloped bottom unit and a flat bottom
unit. The sloped bottom unit relies on particle settling to remove grit. Flow enters the grit chamber
tangentially to provide the longest flow path around the inside of the circular grit chamber. This
longer flow path is designed to achieve a sufficient retention time to allow grit to settle. The sloped
bottom funnels the settled grit into a hopper below the basin. A sloped bottom vortex grit unit cross
section is shown in Figure 5-2.
Figure 5-2. Sloped Bottom Vortex Grit Removal Cross Section
The flat bottom vortex system relies on hydraulic removal instead of specific gravity alone to remove
grit from the wastewater stream. Flat bottom vortex systems use two paddles within the interior of
the grit chamber that induce a toroidal flow pattern to move grit along the bottom towards the
center. Once collected at the center of the grit chamber, a propeller forces excess grit down into the
hopper. A flat bottom PISTA® Grit unit is shown in Figure 5-3.
Figure 5-3. Flat Bottom PISTA® Grit Removal
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5.1.4.2 Vortex Grit Removal Capture Rate
In BC’s experience, it is necessary to de-rate vortex type grit removal units by a factor of 50 percent
of the advertised capacity to achieve satisfactory performance, due to the short detention time in the
chamber. At large flow rates, the small-chambered vortex type units tend to re-suspend smaller grit
particles which become a problem for downstream processes. Table 5-1 lists some advantages and
disadvantages of the vortex type grit removal.
Table 5-1. Induced Vortex–Advantages and Disadvantages
Advantages Disadvantages
• Low maintenance
• Low headloss
• Small footprint
• Re-suspends/low capture rate of fines
• Poor capture efficiency
5.1.4.3 Aerated Grit Removal
Aerated grit chambers are tanks that function specifically to remove inorganic solids from the
wastewater stream. Aerated grit tanks are designed to induce sufficient vertical velocity in order to
separate organic and inorganic solids. In theory, inorganic solids have a higher specific gravity than
organic solids, and therefore require higher vertical velocities to keep them in suspension.
Air diffusers placed near one longitudinal tank wall induce a roll in the contents of the grit tank. This
roll creates maximum velocities near the walls and lower velocities at the surface and bottom of the
tank. The lower transverse horizontal velocities allow inorganic particles to settle out and be
transported to the grit hopper by shear-induced currents.
Aerated grit chamber design is based on providing sufficient hydraulic detention time during peak
wet weather flow (PWWF) conditions. In BC’s experience it is necessary to provide at least
10 minutes of detention time to achieve satisfactory grit removal.
Aerated grit tanks can provide excellent grit removal with minimal headloss, but the chambers
themselves require a larger footprint than induced vortex systems. Proper operation of aerated grit
tanks can be difficult under varying hydraulic loads due to the need to make fine adjustments to the
air diffusers. Figure 5-4 illustrates the particle settling action of an aerated grit chamber.
Figure 5-4. Aerated Grit Removal Schematic
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Table 5-2 lists some advantages and disadvantages of aerated grit chambers.
Table 5-2. Aerated Grit Removal–Advantages and Disadvantages
Advantages Disadvantages
• Low headloss
• Once airflow is dialed in, the maintenance is low
• Effective removal of fines
• Provides additional aeration; “freshens” sewage prior to primary
clarification. Reduces denitrification in primary clarifiers
• Large footprint
• Requires fine tuning diffuser airflow for optimal performance
• High capital cost
• High O&M cost due to blowers
A variation of aerated grit removal technology that can be used in small WWTPs like Naalehu is an
aerated grit trap. A small, aerated tank is provided to allow grit to settle. Aeration is provided to
maintain organic solids in suspension and to “freshen” the influent. Accumulated grit is periodically
removed using a Vactor truck.
5.1.4.4 Lamella Grit Removal
This proprietary technology from Eutek, called the HeadCell, consists of sloped trays stacked in deep
tanks. Flow enters the tanks tangentially and establishes a vortex flow pattern. Solids settle onto
each plate and fall toward an opening at the center of each plate. The grit collects at the cone
shaped bottom of the tank where it is pumped to be washed and dewatered. Effluent flows out of the
trays, over a weir, and into an effluent trough.
Grit capture is all done hydraulically and there are no moving parts. The headloss through each
HeadCell is around one foot. HeadCells can be sized to provide up to 50 mgd of capacity within a
single unit. With the stacked tray design, the HeadCells can achieve a 95 percent capture rate of grit
75 microns and larger. The multiple trays provide a large surface area for settling multiple size
particles. The treatment capacity of the HeadCell is greater than other technologies with the same
footprint. Figure 5-5 is an illustration of a section cut through the HeadCell process.
Figure 5-5. HeadCell Process Schematic
Image courtesy of Eutek
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Table 5-3 lists advantages and disadvantages of the HeadCell.
Table 5-3. Lamella Plate Settling/HeadCell–Advantages and Disadvantages
Advantages Disadvantages
• Effective removal of fines
• Small footprint
• No moving parts
• Low operating cost
• High capital cost
• Short history of installations
5.1.4.5 Grit Particle Size Considerations
Most grit technologies and literature assume that grit is a clean sand or silica particle with a specific
gravity of 2.65. In reality, grit particles are often coated with fats, grease, and organic material that
reduce the particle’s specific gravity. Grit particles with lower specific gravity have lower settling
velocities, behaving like lighter and smaller grit particles.
The sand equivalent size (SES) is the size of a clean sand sphere that exhibits the same settling
velocity as the coated grit particles. For example, a grease coated grit particle with a physical size of
200 microns may settle and behave like a clean particle with an SES of 150 microns.
5.1.4.6 Efficiency comparison
Each of the alternatives claims a minimum particle size and capture rate. These claims are based on
the ideal, clean grit particle. As previously discussed, in reality grit particles are coated with fats and
grease and do not exhibit the behavior of ideal grit particles. The capture rates have to be derated to
reflect the SES of the particles. Table 5-4 compares the claimed minimum particle size captured of
the alternatives discussed.
Table 5-4. Grit Capture Size Comparison
Alternative Targeted Particle Size
Induced Vortex 105 µm
Aerated Grit Removal 105 µm
HeadCell 75 µm
The HeadCell is able to remove the finest particles, with up to 95 percent removal of particles with a
physical size down to 75 microns.
5.1.4.7 Grit Removal Recommendation
A simple aerated grit trap located downstream of the screening process is recommended for the
Naalehu WWTP. Accumulated grit would be periodically removed using a Vactor truck, and dried
onsite in a small drying bed. The dewatered grit would be disposed at the landfill.
An aerated grit trap provides adequate performance with a relatively uncomplicated process.
Although a HeadCell grit removal system could potentially provide a slightly increased grit capture
rate, that benefit is not likely to surpass its significantly higher costs and operational complexity. The
capture rate of an aerated grit trap is sufficient to protect the downstream processes recommended
in this report. High levels of grit removal are particularly important for anaerobic digestors, which are
not anticipated for this facility.
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5.1.5 Odor Control
A common location for foul odor is the headworks of a wastewater treatment plant. This odor is
caused by hydrogen sulfide (H2S), which is formed under anaerobic conditions of the wastewater
collection system. Due to H2S low solubility in wastewater, when there is an excessive concentration
of H2S in the wastewater or if there is turbulence, H2S gas escapes into the atmosphere. This release
produces the distinct rotten egg smell. In addition to H2S, there are other foul odorous compounds
that can be released from wastewater, such as ammonia, amines, diamines, mercaptans, skatole,
and organic sulfides.
Treatment of foul odors can be approached in two ways: preventing odors through liquid treatment
or controlling odors in the gas phase. While liquid treatment provides control of odors prior to their
release, gas phase treatment involves the collection and treatment of gases once they have been
released from wastewater. Treatment methods can be aimed at one type of odor or can treat a range
of odors.
5.1.5.1 Biotrickling Filter
A biotrickling filter consists of a vessel containing plastic or foam media. Foul air is drawn through
the media for treatment. A fixed film biomass is maintained on the media by circulating water over
the media. Liquid fertilizer must be added to the circulating water to provide the nutrients (nitrogen
and phosphorus) the biomass needs to grow. The biomass oxidizes odorous compounds from the
foul air as it travels through the tower. A demister is provided to remove water droplets from the
treated air stream.
Figure 5-6 shows a schematic diagram of a biotrickling filter. Biotrickling filters work best when H2S
concentrations are greater than 10 to 25 parts per million, which is greater than what is expected at
Naalehu, due to the small size of the collection system.
Figure 5-6. Biotrickling Filter
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5.1.5.2 Granular Activated Carbon
A granular activated carbon (GAC) scrubber is recommended for the Naalehu WWTP headworks. A
GAC scrubber passes odorous air through a bed of activated carbon, which adsorbs the odorous
constituents within the pore spaces of the carbon.
Chemical oxidation or reduction of some compounds can also occur. As pore spaces become
occupied, efficiency degrades, and the carbon must be replaced or regenerated. Carbon is most
effective on higher molecular weight molecules such as the organic sulfur compounds, which makes
it the technology of choice. Packaged GAC scrubbers are available for small headworks and vessels
can be situated vertically, horizontally, or radially to optimize footprints and reduce structure
elevation profiles. Figure 5-7 illustrates the process. The County currently operates GAC scrubbers at
other facilities and purchases the GAC media in bulk to reduce costs.
Figure 5-7. Activated Carbon Scrubber
5.1.6 Recommendation
The following are recommended for the Naalehu WWTP headworks:
· Parshall flume influent flow measurement
· Refrigerated automatic composite sampler
· In-channel cylindrical screen with integrated washer
· Aerated grit trap
· Covered channels with foul air collection and GAC scrubber
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5.2 Secondary Treatment
Secondary treatment process provides 5-day biochemical oxygen demand (BOD5), total suspended
solids (TSS), and nutrient removal via biological treatment. This section provides descriptions of
various secondary treatment options including advantages, disadvantages and applicability to the
Naalehu WWTP. The treatment options are then screened to identify technologies for further
evaluation.
5.2.1 Membrane Bioreactor
A membrane bioreactor (MBR) has the smallest footprint of the various biological treatment systems
available and provides the highest quality effluent. An MBR basically combines an aeration basin
with membrane filtration, eliminating the need for tertiary treatment if a very high-quality effluent is
desired for water reuse purposes. Membranes provide an absolute barrier to large particles; TSS
concentrations of the effluent (also known as “filtrate”) are typically less than 1 milligrams per Liter
(mg/L). Effluent from an MBR process can meet stringent water recycling turbidity requirements
without an additional filtration process.
The main difference between MBRs and other biological treatment technologies is the method of
separating the bacteria from the clean water. MBRs have thin membranes with many thousands of
micro-perforations. Depending on the manufacturer, these perforations are 0.04 to 0.2 microns in
diameter, too small for the passage of most microorganisms or other particles present in the
wastewater, but large enough to allow the passage of water molecules.
Figure 5-8 is an illustration of an MBR. Figure 5-9 shows submerged MBR membranes in clean
water.
Figure 5-8. Membrane Bioreactor Illustration
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Figure 5-9. Membrane Cassettes at Johns Creek Environmental Campus
Fulton County, Georgia
Important considerations of an MBR system include:
· Small capacity MBRs can be purchased as a packaged treatment system.
· MBRs can be designed and programmed to achieve nutrient reduction.
· The membrane cost is significant, and membranes must be replaced every 10 to 15 years.
· Membrane fouling can occur with wastewater with high fats, oils, and grease levels.
· MBRs require the use of membrane cleaning chemicals, typically NaOCl and citric acid.
· The process requires a computer control system and is difficult to operate efficiently if the
computer malfunctions.
· The process incurs high electrical power costs, relatively high costs for cleaning chemicals, and
high overall O&M costs. Highly skilled labor is required for some of the O&M tasks.
The MBR process would produce an effluent that is of high quality and has a small footprint, but has
high overall capital, O&M, and life-cycle costs. MBR is retained for further evaluation.
5.2.2 Sequencing Batch Reactor
Sequencing batch reactors (SBRs) are fill-and-draw systems that combine the processes of activated
sludge in a single reactor. The reactor is filled with wastewater, where aeration, settling, and
decanting occurs. By combining these processes, the need for secondary settling is not required.
Denitrification can be achieved by incorporating an anoxic fill step in the cycle or a separate anoxic
zone. A minimum of two SBR reactors are typically used for the process.
SBRs are capable of producing high quality effluent and are potentially space saving in that separate
secondary sedimentation is not needed. However, SBRs are operated by a proprietary computer
control system, cannot be operated in manual mode, and may require influent and/or effluent
equalization (and thus increasing the footprint requirements). Considering these challenges, SBRs
will not be considered further.
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5.2.3 Nereda (Granular Activated Sludge) Process
The Nereda technology is a granular activated sludge process that utilizes proprietary granules in an
SBR. Features of the process include simultaneous fill and draw, fast settling, and approximately 1/5
the footprint of traditional activated sludge systems. The process was developed in Europe and most
current full-scale applications are located in Europe. In the U.S., the process is marketed by Aqua
Aerobic Systems, Inc, according to the supplier website, there are currently only two full-scale
operating systems treating municipal wastewater in the United States. One is a demonstration
facility, and the other is a 3.6 mgd facility in Alabama that began operation in early 2020.
Figure 5-10is a conceptual illustration of the Nereda process. Due to the challenges listed for an SBR
and the lack of long-term operational experience in the United States, the Nereda process is
considered not appropriate for the Naalehu WWTP application.
Figure 5-10. Nereda Process
Courtesy: Aqua Aerobic Systems
5.2.4 Oxidation Ditch
An oxidation ditch is a variation of the complete-mix extended aeration activated-sludge process. The
process generally has a long solids residence time (SRT) and high mixed liquor suspended solids
(MLSS) concentration, making it resilient to upset by peak organic loads. The typical SRT for
oxidation ditches ranges from 15 to 30 days, and the MLSS is generally between 2,000 and
5,000 mg/L. Oxidation ditches are often oval in shape and have been called “racetrack” reactors.
The depth of the ditch typically ranges from 4 to 12 feet. Mechanical aerators in the ditch provide
aeration and mixing. Strategic placement of the aerators creates aerobic and anoxic zones within the
oxidation ditch, for effective nitrification and denitrification. Biological phosphorus removal is also
possible.
Oxidation ditches are usually preceded by preliminary treatment, such as screening and grit removal.
Primary settling is typically not included upstream of oxidation ditch systems. Return activated
sludge is pumped from the secondary clarifier back into the ditch.
Figure 5-11 presents a schematic of an oxidation ditch. Typically, rotating brush or disc mechanical
aerators are used to move mixed liquor around the tank and to provide aeration. The aerators help
mix scum into the water column for treatment. The rigorous mixing action of the mechanical aerators
can generate off-spray. Oxidation ditches are not available as packaged treatment systems. Because
of the large footprint requirements and non-availability of packaged treatment units, the oxidation
ditch process is eliminated from further evaluation.
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Figure 5-11. Typical Oxidation Ditch Schematic
5.2.5 Extended Aeration Activated Sludge Package Plant
Extended aeration is a less-complex system which can operate without primary treatment or
anaerobic digestion. The treatment provides a completely mixed process operated at long hydraulic
detention times and high sludge age. The process uses larger aeration tanks with extended solids
retention times (SRTs) of over 20 days. Careful consideration needs to be given to the capacities of
motors, pumps, and compressors in order to ensure the process can handle variations in flow. The
basic extended aeration process schematic is shown in Figure 5-12.
Figure 5-12. Extended Aeration Process Schematic
The process is generally limited to smaller WWTPs and is often used in prefabricated packaged
plants. The range of typical SRTs on the mainland is 20 to 40 days, and the process generally
operates with MLSSs between 2,000 and 5,000 mg/L. The long SRT and relatively high MLSS makes
the process resistant to shock loading and stable but requires somewhat larger tanks and therefore
incurs higher aeration costs for a given flow, compared to other forms of activated sludge. Sludge
settling can be problematic in the tropics due to denitrification occurring in mixed liquor caused by
the relatively high water temperatures. The process is similar to the oxidation ditch technology
previously described but would use diffused aeration rather than mechanical aeration. The process
is forgiving and resistant to shock loadings. Due to sludge settling challenges in the tropics this
process will not be considered further.
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5.2.6 Activated Sludge with Anoxic Selector
This process is similar to extended aeration but would employ a shorter SRT of less than 10 days and
would operate at a MLSS concentration between 1,500 and 4,000 mg/L. Figure 5-13 shows a
process schematic for this process. The Kihei WWRF and Wailuku-Kahului WWRFs on Maui operate
with this process. The anoxic selector is typically sized to have a volume of approximately 10 to
30 percent of the total aeration basin volume. The process would not be as forgiving and resistant to
shock loadings compared to the oxidation ditch and extended aeration processes due to the shorter
SRT and lower MLSS concentration. But this option is available in a prefabricated package plants
and would incur a smaller footprint than the oxidation ditch and extended aeration processes but
would require operation and maintenance of blowers to provide air to the process. The fine bubble
diffused aeration system would be more efficient than the mechanical aerators generally used in the
oxidation ditch process. This process is retained for further evaluation.
Figure 5-13. Activated Sludge with Anoxic Selector Process Schematic
5.2.7 Recirculating Gravel Filter
Recirculating gravel filter (RGF) technology is an effective technology to treat septic tank effluent
wastewater. After collection and conveyance, the wastewater is treated, in this case using a
recirculating pea gravel filter. RGFs are a relatively simple, but effective means to treat wastewater
from small communities. RGFs have been used to treat flow rates up to 1.0 mgd. RGFs typically
produce a nitrified effluent that contains less than 10 mg/L of BOD5 and TSS (Crites and
Tchobanoglous, 1998).
A schematic diagram of a RGF is shown in Figure 5-14. A septic tank is used to capture settleable
and floatable solids. The septic tank effluent enters a recirculation tank. A dosing pump is used to
apply wastewater in small doses to the top of the filter. The wastewater is treated as it percolates
through the pea gravel media. A network of drainage piping collects the water at the bottom of the
filter and returns it to the recirculation tank. A floating ball recirculation valve controls the return flow
back to the recirculation tank or to the effluent disposal or reuse system. The dosing pump timer
settings and recirculation tank volume are designed so that wastewater will typically flow through the
filter for treatment an average of three to five times before being discharged. An example of a RGF
system in use within a decentralized wastewater system can be found at the Stonehurst subdivision,
located near Martinez, California (Crites, et. al. 1997).
For a community system with conventional sewers and Imhoff tank can be used in lieu of a septic
tank. Imhoff tanks are designed to remove floatable and settleable solids, and also provides for
some digestion of the removed materials.
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Figure 5-14. Recirculating Gravel Filter for Treatment of Septic Tank Effluent
5.2.8 Secondary Treatment Technology Screening
Table 5-5 provides a screening evaluation of the secondary treatment technologies described above.
MBR, activated sludge with anoxic selector, and recirculating gravel filter are carried forward as
project alternatives in Section 7.
Naalehu WWTP Revised PER Section 5 5-15 Table 5-5. Screening of Secondary Treatment Options Criterion MBR SBR Nereda Oxidation Ditch Extended Aeration Activated Sludge with Anoxic Selector Recirculating Gravel Filter BOD5 ≤ 30 mg/L X X X X X X X TSS ≤ 30 mg/L X X X X X X X Nitrification X X X X X X X Total Nitrogen < 10 mg/L X X X X X Anoxic selector X X X X X Appropriate for remote island location X X X X X Appropriate for tropical climate X X X X X X Aeration tank size Small Moderate Small Large Large Moderate Not applicable, but largest overall footprint Secondary clarifier size None None None Largest Largest Large Not applicable, but largest overall footprint Energy requirement Highest Moderate Moderate Moderate Higher Moderate Low Operational complexity High High High Moderate Moderate Moderate Low Available as packaged treatment system X X X X X Fatal flaw Proprietary control systems Limited full scale installations in U.S. Large footprint Large footprint Carry forward in evaluations X X X
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5.3 Disinfection
Disinfection processes selectively kill pathogens or render them incapable of reproduction or harm to
humans. Disinfection at WWTPs is employed for the purposes of protection of public health, reduction
of organic matter, inorganics, nutrients, odor, aesthetics, and maintaining waste-assimilative capacity
of receiving water bodies. The protection of public health through the control of disease-causing
microorganisms is the primary reason for wastewater disinfection (WEF, 1996). As the last barrier of
protection from pathogenic organisms, disinfection at WWTPs is an important process. To address
disinfection, both sodium and calcium hypochlorite system and a UV system were evaluated.
5.3.1 Sodium Hypochlorite
Sodium hypochlorite (NaOCl) is the most commonly used form of liquid hypochlorite. It is an effective
disinfectant at relatively low concentrations. Commonly known as “bleach,” NaOCl can be found in
concentrations ranging from 1.5 to 15 percent. Household bleach usually has a NaOCl concentration
of 3 to 6 percent. Swimming pool sanitizers usually have a NaOCl concentration of 11 to 15 percent.
A concentration of 12.5 percent is commonly used for wastewater treatment and will degrade to
10 percent in 6 to 8 weeks. The product of degradation is chlorine gas. At low concentrations the
product is relatively stable. The solution should be stored in a cool, dark area in a non-corrosive
container. NaOCl is corrosive and toxic.
Scaling can occur in pipes and valves used to transport diluted NaOCl if hardness is present in the
carrier water. The carrier water can be softened prior to mixing with the NaOCl or systems can be
designed to transport undiluted (neat) NaOCl.
Once added to the wastewater, the NaOCl dissociates to form hypochlorous acid and hypochlorite.
The combined amount of hypochlorous acid and hypochlorite is referred to as free chlorine. When
reacted, the compounds formed with the free chlorine also have some disinfecting potential. These
chlorine residuals are desired in some processes, but are toxic to aquatic life if the processed water
is discharged to an open stream. Disinfection with hypochlorite can form DBPs similar to chlorine
gas. For WWTPs, NaOCl can be delivered in bulk or generated on site.
5.3.1.1 Bulk Sodium Hypochlorite
Bulk NaOCl can be obtained in totes, drums, or smaller packages as desired. Currently, NaOCl is
produced on Oahu and transported to neighbor islands in totes. NaOCl solutions are applied with a
metering pump or suction injector. Table 5-6 lists advantages and disadvantages of bulk NaOCl.
Table 5-6. Bulk Sodium Hypochlorite–Advantages and Disadvantages
Advantages Disadvantages
• Able to oxidize at relatively low concentrations
• Use is common at WWTPs
• Readily available
• Simple O&M–application with metering pumps
• Stored and used as a liquid
• Corrosive and toxic
• Degrades quickly at high concentrations and temperatures
• Forms DBPs
• Scaling in pipes and valves can occur
• High transportation cost due to weight of liquid
• 12.5% NaOCl is considered a hazardous chemical. A release of
100 lbs (approximately 12 gallons) or more is considered a
reportable quantity.
• Air binding of pumps is possible at high temperatures due to off-
gassing, but can be mitigated through proper system design.
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The chlorine demand at the Naalehu WWTP is anticipated to be relatively small due to the small
WWTP size and method of effluent disposal. Bulk NaOCl is not recommended due to cost and the
chemical degradation rate in storage.
5.3.1.2 On-Site Generation
On site generation comprises mixing softened water with salt to form brine and then passing an
electric current through the brine to produce NaOCl. When generated on site, the resulting solution is
a relatively weak solution, usually around 0.8 percent. Because the process includes passing an
electrical current through the solution, the electrical power demand can be quite high. Figure 5-15 is
a schematic illustration of NaOCl generation system.
Figure 5-15. Schematic Diagram of an On-site NaOCl Generator
In addition to water hardness, the levels of silica present in the source water can cause build up
problems in the on-site NaOCl generator. The level of pretreatment required is dependent on the
water quality. A detailed water quality analysis would be necessary if this disinfection technology
were chosen. Table 5-7 lists advantages and disadvantages of onsite NaOCl generation.
Table 5-7. Onsite Sodium Hypochlorite Generation–Advantages and Disadvantages
Advantages Disadvantages
• Salt is readily available and inexpensive
• Salt is transported as a solid
• Relatively stable liquid product (low concentration)
• 0.8% solution produced by on-site generation is not
considered a hazardous chemical and is safer to handle
than more concentrated solutions
• Air binding in pumps due to off-gassing less likely to occur
than with more concentrated solutions
• High electrical power demand
• High maintenance requirements
• Generation process generates flammable hydrogen gas
• Disinfection by-products formed
Onsite NaOCl generation is not recommended at the Naalehu WWTP due to the high maintenance
requirements.
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5.3.2 Calcium Hypochlorite
Calcium hypochlorite is the most common solid form of hypochlorite used for disinfection. It can be
found as a powder, granules, pellets, or as tablets in concentrations up to 70 percent. Calcium
hypochlorite will degrade in strength at a rate of 3 to 5 percent per year. Once applied to the
wastewater, the chemistry is similar to that for NaOCl (i.e., bleach). Calcium hypochlorite
decomposes in an exothermic reaction if exposed to moisture.
The solid can be directly applied to wastewater at small WWTPs. Figure 5-16 shows a typical calcium
hypochlorite feed system.
Figure 5-16. Typical Calcium Hypochlorite Feed System
The advantages of using calcium hypochlorite for disinfection at small, remote WWTPs is that it is
available in concentrated form as powder, pellets, or tablets. This makes the transportation and
storage of disinfectant optimal for small WWTPs. Table 5-8 summaries calcium hypochlorite
characteristics.
Table 5-8. Calcium Hypochlorite Summary
Description Characteristic
Transported form Solid
Typical transported concentration 70%
Largest transported volume available 55 pound pails
Decay rate Decays 3-5% per year
Hazards Toxic if ingested (usually through dust or liquid form)
Storage constraints Must be stored in a cool, dry, dark place
Special equipment Tablet feeder
Particular issues Heats and combusts if not stored properly, scaling in pipes, off gassing
5.3.2.1 Dose and Contact Time
The effectiveness of a chlorination system is highly dependent on the characteristics of the
wastewater, the initial mixing and contact time, and the chlorine dose used. For nitrified effluent, the
recommended dose is between 4 and 8 mg/L (Crites and Tchobanoglous, 1998).
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Table 5-9 lists the chlorine demand for various flow conditions. Equipment will be sized to provide
chemical feed at a rate of up to 100 lbs/day, which will ensure an adequate chlorine dose for peak
wet weather discharge flows. The recommended minimum contact time for chlorination is
15 minutes (Ten States Standards Wastewater, Recommended Standards for Wastewater Facilities,
1997, Great Lakes–Upper Mississippi River Board of State and Provincial Public health and
Environmental Managers).
Table 5-9. Chlorine Demand
Description Flow (mgd) Chlorine Demand (lbs/day)
Average dry weather flow 0.125 4-8
Peak day wet weather flow 0.322 11-22
Peak hour wet weather flow 0.457
(317 gpm) 15–31
5.3.3 Ultraviolet Light Disinfection
A common alternative to chlorine disinfection is ultraviolet light (UV). Ultraviolet systems destroy
microorganisms by affecting their deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and
impeding their ability to reproduce. A UV disinfection system is comprised of lamps, a reactor, and
control panel. Wastewater can flow either parallel or perpendicular to the lamps in the reactor, while
the control box provides a starting voltage and maintains the continuous current needed. Currently,
most systems are equipped with an automated lamp cleaning system, to maintain lamp efficiency
levels.
A UV system’s effectiveness is dependent on the characteristics of the wastewater, the dose, and the
exposure time. In the case of UV radiation, the most important factor is the transmittance of the
water, which has a direct effect on the ability of UV light to penetrate through the liquid and reach
microorganisms present at the required intensity. Ideally, the discharge undergoing treatment should
not have a transmittance lower than 55 percent, with the intensity decreasing the farther the
microorganisms are from the lamp. The optimum wavelength to effectively inactivate
microorganisms is between 250 and 270 nanometers.
The main types of UV lamps used for wastewater disinfection are conventional low-pressure lamps,
low pressure high output (LPHO) lamps and medium pressure lamps. Several UV systems include
lamps with automated sleeve cleaning.
5.3.3.1 UV System Design Summary
A UV disinfection system requires about the same size footprint as chlorine at small WWTPs.
Disinfection occurs as the organism is exposed to the UV radiation as the water flows past the UV
lightbulbs. The Trojan UV3000+ system is used at numerous facilities across the U.S., including
some treatment plants in Hawaii. The estimated cost included in this report are based on an
assumed UV transmittance of 65 percent. The amalgam lamp used with the UV3000+ system has an
end-of-lamp-life factor (ELLF) of 0.98 indicating little loss in UV light output over the life of the lamp.
This ELLF has been tested and approved by the State of California and is also accepted by the State
of Hawaii for reuse applications. The system would use LPHO lamps with automatic sleeve cleaning.
LPHO lamps are energy efficient and the UV3000+ system is furnished with automatic sleeve
cleaning devices to reduce labor requirements. Each UV lamp is enclosed in a quartz sleeve to
separate it from the water medium. Each lamp draws 254 watts at full output and is driven by
electronic ballast. The electronic ballast allows the lamps to be dimmed to conserve power based on
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a control signal from a flow meter. The LPHO lamps will have a minimum life of 12,000 hours when
operated in an automatic mode and limited to a maximum of 4 on/off cycles per 24 hours.
Table 5-10 summarizes the size and design criteria for the UV system required to treat the WWTP
discharge.
Table 5-10. UV Disinfection Design Summary
Description Value
Peak Hour Wet Weather Discharge 317 gpm
Minimum UV transmittance 65 percent
No. of UV channels 1
Design dose 35,000 µWs/cm2
Disinfection limit 30 MPN per 100 mL (E.coli)
Validation factors 0.98 end of lamp factor
MPN = most probable number
µWs/cm2 = microwatts per second per square centimeter
5.3.4 Cost Evaluation
A summary of capital and life-cycle estimated costs for both chlorination and UV disinfection is
presented in Table 5-11 for comparison. Additional detail is included in Appendix A. The capital costs
include the materials and equipment costs, construction costs, electrical, instrumentation and
control, soft costs, and contingency. As shown in the table, the UV option incurs higher capital costs.
The life-cycle costs look at the impact of the capital costs along with the annual operations and
maintenance costs, including power, materials, chemicals, and labor costs over the next 30 years.
The life-cycle costs for chlorination option appear to be about 55 percent of the UV option.
Table 5-11. Estimated Disinfection Costs
Description Tablet Chlorination System UV System
Capital Cost $150,000 $1,100,000
Annual Operation and Maintenance $25,000 $10,000
Life-cycle Cost (30-Year Net Present Value) $740,000 $1,340,000
*Does not include annual labor.
5.3.5 Disinfection Recommendation
A tablet chlorination feed system is the recommended disinfection option over the UV system for the
Naalehu WWTP because it incurs lower capital and life-cycle costs. In addition, tablet chlorination will
be more reliable than UV due to frequent “dirty power” conditions on the island. The County may
elect to install a UV system at the Naalehu WWTP should they choose to pursue an R1 water
recycling program in the future.
The proposed effluent management system (subsurface drip irrigation disposal) does not require a
disinfection process to protect human health and the environment because the treated effluent is
dispersed below the ground surface. However, periodic maintenance chlorination of the subsurface
drip system will be required to reduce biofilm fouling within the drip lines.
6-1
Section 6
Solids Management
This section evaluates solids management options for the Naalehu WWTP.
6.1 Aerobic Digestion with Decant Thickening
Aerobic digestion consists of aerating sludge in a tank for an extended period of time. Volatile solids
are oxidized in the process, stabilizing the sludge and reducing the total mass of solids that must be
managed by recycling or disposal. Pathogen densities are also reduced. The process does not
produce biogas. The aerobic digestion process requires substantial energy input in the form of
aeration blowers, and therefore is not typically used at larger (i.e., greater than 10 million gallons per
day [mgd]) wastewater reclamation facilities (WWRFs).
Many small (less than 5 mgd) wastewater treatment plants in the United States use aerobic
digestion to stabilize solids, due to its relatively low capital costs, simplicity, and compatibility with
the certain liquid treatment processes.
Aerobic digestion with decant thickening is a two-stage process that can be achieved in the same
basin. The first stage includes a period of aerobic digestion as described above. In the second stage
the blowers are turned off for a period of time to allow sludge to settle and thicken. Supernatant is
then decanted off the top. The blowers are turned back on to continue the aerobic digestion process.
This process is repeated a few times until the sludge reaches approximately three percent solids. It is
then pumped to the next process.
Aerobic digestion with decant thickening is recommended for the proposed Naalehu WWTP due to its
simplicity, low cost, and effectiveness for small WWRFs.
6.2 Anaerobic Digestion with Biogas Use
Anaerobic digesters are covered tanks equipped with mixing, heating, and biogas collection systems.
Anaerobic bacteria in the digesters convert organic matter into methane, carbon dioxide, and water;
pathogen densities are reduced; and a stabilized sludge is produced. Modern high-rate digesters are
typically single-stage reactors. Mesophilic anaerobic digesters are typically operated at temperatures
between 35 degrees Celsius (°C) and 38°C. Mesophilic digestion systems produce a Class B
biosolids product if the solids retention time (SRT) is greater than 15 days.
Two-stage mesophilic anaerobic digestion, where digesters are operated in series, improves process
performance. The second-stage anaerobic digester generally has less SRT than the first stage. The
advantages of this process configuration are slightly improved volatile solids reduction, a product
with reduced pathogen content, and less product odor potential.
The anaerobic digestion process generates biogas that can be used for digester heating and
generation of electricity.
The mesophilic anaerobic digestion process requires primary sludge to operate effectively. Therefore,
primary clarifiers are required for an anaerobic digestion process. WWRFs that do not have primary
clarifiers must use other digestion technologies.
Anaerobic digestion is cost effective for facilities larger than 5 to 10 mgd. Anaerobic digestion is not
considered to be an appropriate technology for a facility the size of the Naalehu WWTP.
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6.3 Dewatering
A dewatering process is used to remove excess water from digested sludge to form a semi-solid
“cake” product.
6.3.1 Centrifuge Dewatering
Centrifuges are a commonly used dewatering technology. Centrifuges provide the best dewatering
performance of the dewatering technologies presented in this report but require the highest energy
input to do so. High-solids centrifuge machines typically achieve anaerobically digested dewatered
cake of approximately 23 to 28 percent total solids content. Aerobically digested sludge will typically
have lower total solids content, on the order of 12 to 15 percent. The process is shown in Figure 6-1.
Centrifugal force of 500 to 3,000 times the force of gravity is applied to the biosolids within the
centrifuge, separating liquid from the solids. The centrifuge has a solid bowl that spins at a high rate.
Liquid sludge, conditioned with polymer, is introduced within the rotating bowl. The sludge spins with
the bowl, separating into liquid and solid fractions. A screw conveyor mechanism spins within the
rotating bowl at a slightly faster or slower speed than the bowl to facilitate moving the solids fraction
towards one end of the bowl, where it is discharged. The centrate (removed liquid) is discharged
through another port. The process operates continuously. Required ancillary equipment includes
sludge feed pumps, polymer feed systems, and sludge cake conveyance systems.
Centrifuges are sized based on hydraulic and solids throughput. Machines are available to dewater
sludge flow rates ranging from 25 gpm to 700 gpm. High-solids machines can produce a very well-
dewatered material, if anaerobic digestion is used.
Centrifuges require a high level of operator due to the high rotational speed. For this reason, they are
typically not used at small WWTPs like Naalehu.
Figure 6-1. Centrifuge Dewatering
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6-3
6.3.2 Screw Press Dewatering
The screw press represents a relatively new technology for dewatering municipal wastewater solids,
although the technology has been used successfully in industrial, pulp and paper production,
chemical, and food processing applications.
Figure 6-2 shows a diagram of a screw press. Thickened sludge, conditioned with polymer, is
introduced to the machine in the head box at the inlet end. The mixture is conveyed from the inlet
end to the outlet end of the press by the rotating screw. As the material is conveyed along the length
of the press it is squeezed between the tapered screw shell and the screen drums. The dewatered
solids exit the press at the discharge end and fall down the discharge box. The adjustable pressure
cone provides back pressure within the machine, particularly when the machine is initially filled. For
municipal wastewater solids applications, the pressure cone is typically not needed after the
machine is filled; the dewatered sludge provides sufficient back pressure. The liquid that was forced
out through the screens is returned to the liquid treatment process.
Figure 6-2. Screw Press Diagram
The screw press operates at a very slow rotational speed. The screw rotation is usually one-half of a
revolution per minute or less for municipal wastewater solids. Water is slowly forced from the sludge
by squeezing action–similar to a belt filter press–but for much longer periods of time. The solids
retention time in a screw press can be on the order of 2 hours. The simplicity of screw presses
makes them practical for small wastewater treatment plants, such as Naalehu.
6.4 Disposal
Dewatered solids, grit, and screenings would be trucked to the West Hawaii Landfill for disposal.
7-1
Section 7
Project Alternatives Evaluations
This section presents evaluations of the three project alternatives developed for the new wastewater
treatment plant (WWTP).
7.1 Project Alternative Descriptions
Three project alternatives were developed as part of the tasks completed for this Preliminary
Engineering Report. All three alternatives include a new C Brewer house lot collection system (i.e.,
Phase 1 + Phase 2), WWTP, and subsurface drip effluent disposal system.
7.1.1 Project Alternative 1: Activated Sludge with Anoxic Zone Package Plants
Project Alternative 1 is comprised of an activated sludge process with anoxic zone provided in the
form of packaged treatment systems. A typical packaged treatment system of this type would include
the following elements:
· Flow equalization
· Anoxic treatment zone
· Aerobic treatment zone
· Secondary clarifier
· Aerobic digester with decant thickening
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7-2
Figure 7-1 presents a sketch of Project Alternative 1. Wastewater would receive preliminary
treatment in the headworks before flowing into the packaged treatment system. Two package
treatment units would be provided, each with 62,500 gallons per day (gpd) capacity. Effluent would
flow into an irrigation equalization tank before being applied to the subsurface drip disposal system.
Digested solids would be dewatered using a screw press prior to disposal at the landfill.
Figure 7-1. Project Alternative 1: Activated Sludge with Anoxic Zone Package Plants
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7-3
7.1.2 Project Alternative 2: MBR Package Plants
Project Alternative 2 is similar to Project Alternative 1 but includes two MBR package plants to
provide treatment. Figure 7-2 provides an outline of Project Alternative 2. The MBR technology would
create effluent that could be recycled for irrigation and/or stock watering purposes, if desired in the
future. However, recycled water distribution costs are not included in the evaluations below to allow
all alternatives to be considered on an equal basis.
Figure 7-2. Project Alternative 2: MBR Package Plants
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7-4
7.1.3 Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter
Project Alternative 3 incorporates recirculating gravel filter treatment technology. Figure 7-3 provides
a schematic of the project alternative. An Imhoff tank would be provided downstream of the
headworks to remove grease and settleable solids prior to flowing into a recirculation tank.
Recirculation pumps would distribute water from the recirculation tank over the surface of the pea
gravel filter that provides secondary treatment. Water collected at the bottom of the filter would flow
back to the recirculation tank. On average water would flow through the filter five times before
disposal in the subsurface drip irrigation system as previously described.
Figure 7-3. Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter
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7-5
7.2 Cost Evaluations
Capital, operations and maintenance (O&M), and life-cycle cost evaluations are presented in this
section.
7.2.1 Capital Costs
Conceptual cost estimates were created for the three project alternatives. The cost estimates were
developed using construction bids from similar projects, quantity take-offs, vendor quotes, and other
sources. The costs were adjusted to account for economies of scale and construction inflation since
the bid opening date. Where Hawaii costs were unavailable, U.S. mainland costs were used after
adjustment to reflect Hawaii Island conditions.
In accordance with the Association for the Advancement of Cost Engineering International (AACE)
criteria, these are Class 5 estimates. A Class 5 estimate is defined as a Conceptual Level or Project
Viability Estimate. Typically, engineering is from 0 to 2 percent complete. Class 5 estimates are used
to prepare planning level cost scopes or evaluation of alternative schemes, long range capital outlay
planning.
Expected accuracy for Class 5 estimates typically ranges from -50 to +100 percent, depending on
the technological complexity of the project, appropriate reference information and the inclusion of an
appropriate contingency determination. In unusual circumstances, ranges could exceed those
shown. Table 7-1 provides a summary of capital cost assumptions used.
Table 7-1. Capital Cost Estimating Assumptions
Description Value
Estimate date June 2023
Engineering News Record 20-Cities Average Construction Cost Index 13,345
Electrical and instrumentation markup 25 percent
Engineering, administration, and legal markup 25 percent
Estimating contingency for unknowns 20 percent
Table 7-2 provides a summary of the capital cost estimates, in current (June 2023) dollars. Detailed
estimates can be found in Appendix A.
Table 7-2. Capital Cost Estimates Summary
Description Alternative 1:
Activated Sludge Package Plants
Alternative 2:
MBR Package Plants
Alternative 3:
Imhoff Tank/RGF
Collection system $40.2 million $40.2 million $40.2 million
Drainage channel improvement $19.9 million $19.9 million $19.9 million
Wastewater treatment $20.7 million $20.3 million $29.6 million
Effluent disposal $4.0 million $4.0 million $4.0 million
Totals $84.7 million $84.3 million $93.6 million
AACE Class 5 estimate range $42.4–$169.5 million $42.2–$168.6 million $46.8–$187.2 million
As shown in the table, all three project alternatives have similar capital costs, and can be considered
equal at this level of analysis.
Naalehu WWTP Revised PER Section 7
7-6
7.2.2 Operation and Maintenance Costs
O&M costs estimates were developed for the three alternatives. The O&M cost estimates include
collection system maintenance, plus estimates of labor, electricity consumption, chemicals,
maintenance materials and solids disposal for the WWTP. O&M assumptions are listed in Table 7-3.
The O&M estimates are based on the WWTP average dry weather flow capacity.
Table 7-3. O&M Cost Assumptions
Description Value
Average dry weather flow 125,000 gpd
Labor cost, loaded $100,000/year/full time equivalent
Electricity cost $0.45/kWh
Landfill tip fee $116/wet ton
Maintenance materials 2 percent of equipment capital cost/year
The O&M estimates for the three project alternatives are summarized in Table 7-4. Details can be
found in Appendix A. Per Table 7-4, Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter
incurs the lowest O&M cost, while Project Alternative 2: MBR Package Plants incurs the highest.
Table 7-4. O&M Cost Estimate Summary
Description
Annual Cost
Project Alternative 1:
Activated Sludge Package Plants
Project Alternative 2:
MBR Package Plants
Project Alternative 3:
Imhoff Tank/RGF
Collection system $74,000 $74,000 $74,000
Labor $300,000 $300,000 $300,000
Electricity $270,000 $300,000 $120,000
Chemicals $27,000 $32,000 $27,000
Maintenance materials $117,000 $113,000 $84,000
Solids disposal $67,000 $67,000 $67,000
Totals $855,000 $886,000 $672,000
7.2.3 Life-Cycle Costs
An economic evaluation was prepared to assess the potential life-cycle costs associated with each
project alternative. The economic evaluation consists of a net present value (NPV) comparison. The
NPV analysis includes capital, O&M, and equipment replacement costs. An appropriate inflationary
factor and discount rate are applied to obtain the NPV over a 30-year planning period.
The NPV of an alternative represents the amount of money that would need to be set aside today (at
a given interest rate) to pay the costs associated with the alternative over the entire planning period.
The alternative with the lowest NPV is considered the most attractive from an economic perspective.
The evaluation results are included in Appendix A.
Naalehu WWTP Revised PER Section 7
7-7
Table 7-5 summarizes the life-cycle cost evaluation assumptions.
Table 7-5. Life-Cycle Economic Assumptions
Description Value
Year of analysis 2023
Planning period, years 30
Inflation rate, percent 3.5
Discount rate, percent 5.0
Equipment replacement cycle, years 20
Membrane replacement cycle, years 15
Table 7-6 summarizes the results of the life-cycle cost analysis.
Table 7-6. Life-Cycle Cost Analysis Summary
Description Alternative 1:
Activated Sludge Package Plants
Alternative 2:
MBR Package Plants
Alternative 3:
Imhoff Tank/RGF
Capital cost $84.8 million $84.3 million $93.6 million
Annual O&M cost $855,000 $886,000 $672,000
Equipment replacement cost
(excluding membranes) $6.3 million $6.0 million $4.6 million
Membrane replacement cost N/A $60,000 N/A
Life-cycle cost $109.6 million $109.8 million $112.9 million
Comparison to lowest cost alternative 0% +0.2% +3.0%
Figure 7-4 shows the results in graphical form. As shown in the table and graph, the three project
alternatives have similar capital costs. Alternative 1: Activated Sludge Package Plants and
Alternative 2: MBR Package Plants incur nearly equivalent life-cycle costs due to the similarities in
design and package plant capital costs. Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter
incurs the greatest life-cycle costs, largely due to the high capital cost associated with the Imhoff
tank and recirculating gravel filter beds. At this level of analysis all three project alternatives can be
considered to have similar life-cycle costs.
Naalehu WWTP Revised PER Section 7
7-8
Figure 7-4. Life-Cycle Cost Evaluation Results
7.3 Non-Economic Evaluation
A non-economic evaluation was conducted to provide a qualitative comparison between the three
alternatives.
7.3.1 Approach
Non-economic evaluations are generally subjective by necessity. Quantifiable measurements are
used when available, but lack of information or difficulty and expense of obtaining information
requires subjective assessments.
The project alternatives were scored in relation to one another and according to an evaluation
matrix, described below. Each alternative was scored from 1 to 5 (5 = high/desirable, 1 = low/less
desirable) for each evaluation criteria. The alternatives were not ranked in the scoring; alternatives
could receive the same scores for any given criteria.
The evaluation criteria were weighted to reflect their overall significance for the project. The scores
were multiplied by the criteria weights to develop a non-economic score for each alternative.
$84,751,000 $84,329,000 $93,602,000
$24,805,000 $25,448,000
$19,250,000
$0
$20,000,000
$40,000,000
$60,000,000
$80,000,000
$100,000,000
$120,000,000
Project Alternative 1
Activated Sludge
Package Plants
Project Alternative 2
MBR Package Plants
Project Alternative 3
Imhoff Tank / RGFLife-cycle Cost (30-yr NPV)Capital Cost O&M and Replacement Cost
Naalehu WWTP Revised PER Section 7
7-9
7.4 Non-Economic Evaluation Criteria
Table 7-7 shows the non-economic criteria chosen for comparing the three alternatives.
Table 7-7. Non-Economic Comparison Criteria
Category Criteria Description
Level of Service
Measures
Effluent quality The quality of the effluent produced with respect to BOD5, TSS, nutrients, and
turbidity.
Potential for capacity expansion Ability of the system to be expanded should additional capacity be required.
Water recycling feasibility The relative extent of modifications that would be needed to create R-1 recycled
water to support a future water recycling program.
Public perception/community
concerns The community’s impression of the project and the perceived support.
Regulatory
Monitoring complexity The relative difficulty of monitoring tasks required for the option chosen.
Treatment adjustment potential The ability to increase treatment to comply with future permit requirements and/or
growth.
Safety regulations complexity The relative difficulty to comply with safety regulations including staff training,
reporting, maintenance procedures.
Environmental concerns The extent of the project’s potential environmental impacts should failures occur.
O&M Factors
Footprint The physical space that the processes will occupy (affecting land acquisition,
subdivision, and permitting).
Safe work environment
The relative health and safety risk operation of given option will have on the
employees; includes equipment access, chemical hazards, confined spaces, dust,
etc.; the extent of measures required to ensure the health and safety of the
employees.
Maintenance complexity The relative intensity of equipment maintenance requirements.
Operations complexity The relative intensity of the operations requirements.
Island Factors
Mainland delivery dependence The relative dependence on regular deliveries of equipment, supplies, or spare parts
from mainland sources.
Mainland servicing dependence The relative degree to which technology will require special servicing by mainland-
based personnel.
Power dependence The relative degree to which the treatment processes depend on electrical power for
operation.
Chemical dependence The relative dependence on chemical supplies, whether locally available or restricted
by mainland delivery schedules and requirements.
The categories and criteria were developed using best engineering judgment and our understanding
of the project, and the County of Hawaii Department of Environmental Management goals and
concerns.
Naalehu WWTP Revised PER Section 7
7-10
The weighting factors used for the non-economic comparison are listed in Table 7-8.
Table 7-8. Non-Economic Comparison Criteria Weighting Factors
Category Criteria
Level of Service Measures
(25%)
• Effluent quality (30%)
• Potential for capacity expansion (20%)
• Water recycling feasibility (30%)
• Public perception/community concerns (20%)
Category Total (100%)
Regulatory
(25%)
• Monitoring complexity (25%)
• Treatment adjustment potential (25%)
• Safety regulations complexity (25%)
• Environmental concerns (25%)
Category Total (100%)
Owner Factors
(25%)
• Footprint (30%)
• Safe work environment (25%)
• Maintenance complexity (25%)
• Operations complexity (20%)
Category Total (100%)
Island Factors
(25%)
• Mainland delivery dependence (25%)
• Mainland servicing dependence (25%)
• Power dependence (25%)
• Chemical dependence (25%)
Category Total (100%)
Overall Total 100%
7.5 Non-Economic Evaluation Results
A score of 1 through 5 was given for each criterion, with 5 being the most favorable, and 1
representing the least desired option. The complete non-economic evaluation is included as
Appendix C. The non-economic evaluation results are summarized in Table 7-9.
Table 7-9. Non-Economic Weighted Scores
Alternative Score Rank
Project Alternative 1: Activated Sludge Package Plants 3.80 2
Project Alternative 2: MBR Package Plants 3.96 1
Project Alternative 3: Imhoff Tank/Recirculating Gravel Filter 3.53 3
As shown in Table 7-9, Project Alternative 2: MBR Package Plants, received the highest non-
economic score. The higher score reflects the County’s desire to standardize on MBR technology to
provide the highest level of treatment at WWTP facilities and to facilitate future water recycling
programs.
Naalehu WWTP Revised PER Section 7
7-11
7.6 Conclusions and Recommendation
Figure 7-5 combines the economic and non-economic results into a single graph. As previously
stated, the economic cost of the three project alternatives can be considered equivalent at this level
of analysis. Project Alternative 2: MBR Package Plants, has the highest non-economic score and is
recommended for implementation if the County proceeds with a centralized sewer system and WWTP
for the community.
Figure 7-5. Combined Economic and Non-Economic Results
1
2
3
4
5
0 20 40 60 80 100 120Non-Economic ScoreLife-cycle Cost ($ million)
Alternative 1: Activated Sludge Package Plants
Alternative 2: MBR Package Plants
Alternative 3: Imhoff Tank/Recirculating Filter
8-1
Section 8
Preliminary Design of
Improvements
This section presents an overview of preliminary design improvements proposed for the new
Naalehu wastewater treatment plant (WWTP) project.
8.1 Site Plan
Figure 8-1 provides a preliminary site plan of the WWTP project.
8.2 Process Schematic
Figure 8-2 provides a preliminary process schematic of the WWTP.
TMK:
(3)9-5-010:029
MAMALAHOA HIGHWAY
750' RADIUSXXX
X
X
X
X
X
X
X
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XXXXXXXXXXXXXXXXX X X X X
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TMK:
(3)9-5-022:009
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Path: C:\bcpw\d3321813File Name: 153740-FIG-8-1-WWTP-PreliminarySitePlan Plot Date: July 17, 2023 3:32 PM Cadd User: Richard SellonaFIGURE
DATE: July 17, 2023
NAALEHU WASTEWATER TREATMENT PLANT
153740 PRELIMINARY SITE PLAN 8-1
SCALE: 1" = 200'
DRAINAGE
EASEMENT D-3
(3.2± ACRES)
TMK: (3)9-5-007:016
TMK: (3)9-5-021:015
TMK: (3)9-5-022:001
EXISTING
VEGETATED
DRAINAGE OUTLET
EXISTING HIGHWAY
CULVERT
EXISTING VEGETATED
DIVERSION CHANNEL
WWTP
PROPERTY LIMIT
FUTURE DRIP
ZONE 5
FUTURE DRIP
ZONE 6
1,000' WELL
SETBACK
WELL
STA 0+00 START REALIGNMENT
DRAINAGE DIVERSION CHANNEL
STA 15+08 END
REALIGNMENT
DRAINAGE DIVERSION
CHANNEL. PROPOSED
OUTLET RELOCATION
STA 8+00
DRIP ZONE 4
DRIP ZONE 3
HEADWORKSBULK FUEL
STORAGE TANK
POTABLE
WATER TANK
CULVERT
ACCESS AND
UTILITY EASEMENTS
LOT 1
(14.9± ACRES)
DRAINAGE
EASEMENT D-1
(0.2± ACRES)
DRAINAGE
EASEMENT D-2
(1 ACRE)
FENCE SURROUNDS
FACILITY
FENCE SURROUNDS
FACILITY
LOCKED
GATE
FENCE SURROUNDS
FACILITY
FENCE SURROUNDS
FACILITY
SCALE IN FEET
0 250 500
IRRIGATION
CONTROL TANK &
EFFLUENT PUMP
DRIP ZONE 2
DRIP ZONE 1
MBR PACKAGE
PLANTS
FUTURE PACKAGE
PLANTS EXPANSIONGRIT DRYING
BED
INFLUENT PUMP
STATION
OPERATIONS
BUILDING
SUBSURFACE DRIP
IRRIGATION DISPOSAL
(5.2± ACRES)
FUTURE DISPOSAL
EXPANSION
(3.5± ACRES)
SUBSURFACE
DRIP ZONE 1
SUBSURFACE
DRIP ZONE 2
SUBSURFACE
DRIP ZONE 3
SUBSURFACE
DRIP ZONE 4
EXISTING VEGETATION
FUTURE
DRIP ZONE 5
FUTURE
DRIP ZONE 6
GRIT REMOVAL
INFLUENT
AEROBIC
DIGESTER
TRUCK TO
LANDFILL
EFFLUENT
SAMPLER
RAS
ANOXIC PRE-
AERATION
MEMBRANES
MBR PACKAGE PLANTS (2)
PERMEATE
CUT THROAT
FLUME
WAS
PARSHALL
FLUME
MMAGNETIC
FLOW METER
IRRIGATION
CONTROL TANK
M
M
M
M
CHLORINE
(HYPOCHLORITE)
MANUAL BAR
RACK
FINE SCREEN
DISPOSAL
Path: C:\bcpw\d3321813File Name: 153740-FIG_8-2 Plot Date: July 26, 2023 9:17 AM Cadd User: Richard SellonaFIGURENAALEHU WASTEWATER TREATMENT PLANT
JOB NO: 153740 PROCESS SCHEMATIC 8-2
SCALE: NONE
INFLUENT
SAMPLER
POLYMER
M
M
SCREW PRESS
DEWATERING
FUTURE
EFFLUENT
SAMPLER
FUTURE R-1
REUSE
FUTURE UV
DISINFECTION
FUTURE
TURBIDIMETER
INFLUENT PUMP
STATION
EFFLUENT PUMP
FUTURE R-1
EFFLUENT PUMP
EXISTING VEGETATION
EXISTING VEGETATION
EXISTING VEGETATION
EXISTING VEGETATION
EXISTING VEGETATION
Naalehu WWTP Revised PER Section 8
8-4
8.3 Preliminary Design Criteria
Table 8-1 lists the preliminary design criteria for the proposed WWTP.
Table 8-1. Preliminary Design Criteria
Description Value
Influent Flow
Average dry weather, gallons per day (gpd) 125,000
Peak day wet weather, gpd 322,000
Peak hour wet weather, gpd (gallons per minute [gpm]) 457,000 (317)
Influent Characteristics
Biochemical oxygen demand (BOD5), mg/L 300
Total suspended solids (TSS), mg/L 300
Total Nitrogen (TN), mg/L 40
Odor Control–Granular Activated Carbon
Airflow rate, air changes per hour 6
H2S inlet concentration, parts per million 1-10
H2S removal efficiency, percent 99
Media, type High-capacity carbon
Mechanical Screens
Number of units, each 1
Type In-channel cylindrical
Screen opening size, inches/(millimeters) 0.125 /(3)
Maximum flow rate capacity, gpm Greater than 480
Screening washing Integral
Screening compaction Integral
Bypass Screen
Type Manually-cleaned bar rack
Bar spacing, inches 1
Rake Fabricated to Interlock with bars
Screenings Receptacle
Type 55-gallon drum or bags
Screenings volume per million gallons (Mgal) treated, ft3/Mgal 5
Estimated screenings quantity, ft3/day 0.63
Disposal frequency, per week 1
Influent Flow Metering
Type Parshall flume
Maximum flow capacity, gpm Greater than 480
Minimum straight upstream channel section 20 times the throat width
Influent flow sampling Refrigerated automatic composite sampler
Naalehu WWTP Revised PER Section 8
8-5
Table 8-1. Preliminary Design Criteria
Description Value
Grit Chamber
Number of units, each 1
Type Aerated grit trap
Volume, gallons 4,800
Detention time, minutes at Peak Hour Wet Weather Flow 10
Air supply, ft3/minute 90
Removal Vactor truck
Estimated average grit quantity, ft3/day 1.4
MBR Package Plant
Number of packaged biological treatment trains, each 2
Flow basis for biological design, gpd each 62,500
Anoxic tank working volume (excluding membranes), gallons each 2,000
Aerobic working volume, gallons each 10,000
Design SRT, days 7
Waste sludge removal, gpd each 1,500
Design mixed liquor suspended solids concentration in bioreactor, mg/L ≤ 8,000
Number of duty membrane blowers, per train 1
Number of duty process aeration blowers, per train 1
Aeration system, type Coarse bubble diffused aeration
Mixed liquor recirculation rate, x Average Dry Weather Flow 4
Membrane cleaning dosing systems, types Sodium hypochlorite, citric acid, and coagulant
Sludge Management System
Number of units, each 1
Type Incline screw press
Screw press capacity, gpm 45
Polymer dose, lbs/dry ton 20
Annual polymer use, lbs 621
Average amount of dewatered sludge, wet tons/day 0.71
Disposal frequency, per week 1
Maintenance Disinfection system
Type Chlorine
Form Calcium hypochlorite tablets
Design chlorine dose, mg/L 8
Irrigation Equalization (Control) Tank
Number of units, each 1
Type Glass lined bolted steel
Volume, gallons 20,000
Drip flow, gpm 112
Effluent Flow Metering
Type Magnetic
Effluent flow sampler Refrigerated automatic composite
Naalehu WWTP Revised PER Section 8
8-6
Table 8-1. Preliminary Design Criteria
Description Value
Effluent Quality
BOD5, mg/L ≤ 5
TSS, mg/L ≤ 5
TN, mg/L ≤ 10
Turbidity, nephelometric turbidity units ≤ 0.2
Effluent Management System
Type Subsurface drip irrigation disposal
Number of units. each 2 (1 active, 1 redundant)
Distribution system Non-clog subsurface drip emitters
Design percolation rate, inches/day 2.50
Design application rate, % of percolation rate 4
Total land application area, acres 5.2
Number of irrigation zones 4
Area per zone, sq. ft. 56,630
Flow rate per zone, gallons per minute 112
Drip rate per emitter, gallons per hour 1
Total number of emitters, each 26,833
Total length of drip line, ft 53,667
Depth of drip line, inches 6–9
Drip line spacing, ft 4.2
Emitter spacing, ft 2
Vegetation Existing vegetation
Irrigation system monitoring Flow meter(s) and pressure indicators
Stormwater site management 10-year, 1-hour storm
8.4 Preliminary Floor Plan
Figure 8-3 provides a preliminary floor plan for the proposed Operations Building.
MAINTENANCE AND STORAGE
ROOM
SINK AND
COUNTER SPACE
ELECTRICAL
ROOM
12' WIDE ROLL-UP DOOR
DESK AND
WORK SPACE GENERATOR ROOM
WITH VENTILATION
MOTOR
CONTROL
CENTER
6' MIN
CMU
BLOCKS
SLUDGE
DEWATERING
EQUIPMENT
BLOWER ROOM
Path: C:\bcpw\d3083617File Name: 150440-FIG-OpsBldg Plot Date: July 13, 2023 12:53 PM Cadd User: Richard SellonaFIGURENAALEHU WASTEWATER TREATMENT PLANT
JOB NO: 153740 OPERATIONS BUILDING PRELIMINARY FLOOR PLAN 8-3
SCALE: 3/16" = 1'-0"
0 2'8'
SCALE: 3/16" = 1'-0"
4'12'1'3'
9-1
Section 9
Implementation Plan
This section describes the proposed implementation plan for the Naalehu wastewater treatment
plant (WWTP).
9.1 Implementation Approach
The WWTP and collection system projects could be implemented using either a traditional
design/bid/build (DBB) approach or a design/build (DB) approach, as discussed below.
9.1.1 Design Bid Build Approach
DBB is the traditional approach used by the County for implementing public works projects. The
design is prepared by a consultant, and then bids are solicited from construction contractors. The
County awards the contract to the lowest responsible bidder.
Advantages of the DBB approach are that the County retains maximum control over the design
process, ensuring the project will meet its needs.
9.1.2 Design Build Approach
DB is an alternative delivery approach whereby the County would contract with an entity to both
design and construct a facility that meets established project specifications. The combined WWTP
and collection system projects are large enough monetarily for the County to consider a DB
approach. The County would need to use a procurement process based on qualifications and cost to
select the DB entity. The typical DB procurement process takes 9–12 months to complete. The DB
bidders will need the County to complete the following prior to the DB procurement process:
· Complete geotechnical report
· Environmental assessment
· Land use entitlements
· WWTP land purchase
Advantages of DB implementation are:
· Possibility of reduced overall costs
· Design and construction can occur simultaneously, potentially reducing implementation time
· DB entity assumes the performance liability for the project, as defined in the project
specifications
Disadvantages of the DB approach are that the County has limited experience with it, and the County
would not have as much control over how the project is designed.
Naalehu WWTP Revised PER Section 9
9-2
9.2 Implementation Schedules
Planning level implementation schedules were developed for both approaches.
9.2.1 Recent Change in State of Hawaii Land Use Commission Policy
The State of Hawaii Land Use Commission (LUC) recently changed its policy regarding the use of
Special Permits for non-conforming uses. The proposed WWTP site is located in the Agricultural
District as defined by the LUC. A WWTP is not an allowable land use in the Agricultural District. In the
past the LUC has allowed Special Permits to be used for non-conforming uses. However, in response
to litigation the LUC has recently changed its policy and now recommends that project proponents for
permanent facilities (like a WWTP) pursue a District Boundary Amendment (DBA) from the LUC. The
LUCs rationale is that permanent entitlement (i.e., a DBA) is more appropriate for a permanent
facility like a WWTP, rather than a temporary entitlement like a Special Permit. Since the WWTP
parcel is less than 15 acres the DBA can be processed by the County of Hawaii. However, the action
will likely take longer to implement than a Special Permit.
9.2.2 Equipment Procurement Time to Impact Construction Schedule
The COVID-19 pandemic continues to impact the construction industry due to increased time to
deliver equipment and other materials. Most significantly, the time for the MBR package plant
supplier to manufacture their equipment was quoted at 55 weeks instead of a typical pre-pandemic
time of approximately 26 weeks. Similar delays are being experienced on other construction projects
in Hawaii, and it is reasonable to assume that other equipment suppliers will quote extended supply
times. As a result, we now suggest that a construction schedule of 2 years is a reasonable
expectation.
9.2.3 Implementation Schedules
Figure 9-1 presents implementation schedules for both approaches. At this time, both approaches
may not enable the County to meet the Administrative Order on Consent (AOC) milestone schedule to
close the LCCs. The DB approach offers greater potential to meet the milestone, because equipment
procurement can possibly occur in parallel with design within a DB contract.
9.3 Recommendation
Given the Revised AOC deadline to close the LCCs, and the equipment procurement time impact to
the construction schedule, a DB approach may offer a better opportunity to meet the deadline,
because a DB entity could initiate equipment procurement while design activities progress. If the U.S.
Environmental Protection Agency was able to grant a time extension, then either a DBB or DB
approach can be taken. A traditional DBB approach would give the County greater control over the
project outcome, and is the County’s standard method for implementing projects.
Naalehu WWTP Revised PER Section 9 9-3 Figure 9-1. Implementation Schedules
10-1
Section 10
References
Brown and Caldwell (November 2019). Feasibility Study: Naalehu WWTP R-1 Stock Water, Prepared for County of
Hawaii Department of Environmental Management Wastewater Division.
Crites, Ron, Craig Lekven, Steve Wert, George Tchobanoglous (1997). A Decentralized Wastewater System for a
Small Residential Development in California. The Small Flows Journal. National Small Flows Clearinghouse.
Volume 3, Issue 1, Winter 1997.
Crites, R. W. and G. Tchobanoglous (1998) Small and Decentralized Wastewater Management Systems, McGraw-Hill,
New York.
Department of Wastewater Management, City and County of Honolulu, State of Hawaii. Design Standards of the
Department of Wastewater Management, Volume 1 and 2. July 2017.
Great Lakes–Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers.
Recommended Standards for Wastewater Facilities. 1997.
Hawaii Administrative Rules, Title 11, Department of Health Administrative Rules.
Masa Fujioka & Associates. Letter Report, Probing for Large Cavities (Lava Tubes), Naalehu and Pahala Large
Capacity Cesspool Sewerage System. January 9, 2007.
M&E Pacific, Inc. Kau Sewer System Evaluation, Kau, Island of Hawaii, Hawaii. December 2004.
SSFM International, Inc. Final Preliminary Engineering Report for Naalehu and Pahala Large Capacity Cesspool
Conversion Projects, July 2007.
USEPA. “Process Design Manual, Land Treatment of Municipal Wastewater Effluents”. EPA/625/R-06/016.
September 2006.
Water Environment Federation. Wastewater Disinfection, Manual of Practice FD-10. Water Environment Federation,
1996.
Naalehu WWTP Revised PER
A
Appendix A: Cost Estimates
Naalehu WWTP
Revised Preliminary Engineering Report
Alternative Solutions Cost Summary
Collection System TOTAL $40,165,000
Drainage Channel TOTAL $19,865,000
$20,705,000
Effluent Disposal TOTAL $4,016,000
$84,751,000
ANNUAL O&M COSTS
Collection system $74,000
Labor $300,000
Electricity $270,000
Chemicals $27,000
Maintenance materials $117,000
Solids disposal $67,000
Total Annual Operating Costs $855,000
EQUIPMENT REPLACEMENT COST (20 YEAR)$6,238,000
Collection System TOTAL $40,165,000
Drainage Channel TOTAL $19,865,000
$20,283,000
Effluent Disposal TOTAL $4,016,000
$84,329,000
ANNUAL O&M COSTS
Collection system $74,000
Labor $300,000
Electricity $300,000
Chemicals $32,000
Maintenance materials $113,000
Solids disposal $67,000
Total Annual Operating Costs $886,000
MEMBRANE REPLACEMENT COST (15 YEAR)$60,000
EQUIPMENT REPLACEMENT COST (20 YEAR)$6,005,000
Collection System TOTAL $40,165,000
Drainage Channel TOTAL $19,865,000
$29,556,000
Effluent Disposal TOTAL $4,016,000
$93,602,000
ANNUAL O&M COSTS
Collection system $74,000
Labor $300,000
Electricity $120,000
Chemicals $27,000
Maintenance materials $84,000
Solids disposal $67,000
Total Annual Operating Costs $672,000
EQUIPMENT REPLACEMENT COST (20 YEAR)$4,574,000
Alternative #1 - RAS Package Plants / Subsurface Drip
ALTERNATIVE #1 CAPITAL COST TOTAL
Alternative #2 - MBR Package Plants / Reuse / Subsurface Drip
Wastewater Treatment TOTAL
ALTERNATIVE #3 CAPITAL COST TOTAL
Wastewater Treatment TOTAL
ALTERNATIVE #2 CAPITAL COST TOTAL
Alternative #3 - Imhoff Tank / RGF / Subsurface Drip
Wastewater Treatment TOTAL
Naalehu WWTP
Revised Preliminary Engineering Report
Unit Cost Estimates
Electrical & Instrumentation 25.0%
Engineering, Admin, & Legal 25.0%
Contingency 20.0%
ENR CCI 13,345.00 June, 2023
Naalehu WWTP Capital Unit Costs Units Unit Cost
Environmental protection, BMPs ac $11,000
Site clearing ac $20,000
Site roads, guard rails, pavement ac $92,000
Perimeter fence LF $150
WWTP site grading ac $30,000
WWTP site drainage improvements ac $18,000
Drainage channel improvements LS $13,700,000
Plant water catchment/collection system LS $75,000
Process yard piping LS $250,000
Headworks (includes site/civil, structures, equipment & piping)LS $1,024,000
Influent pump station LS $1,670,000
Chlorine disinfection LS $150,000
RAS package plants LS $3,812,000
MBR package plants LS $3,579,000
Irrigation equalization tank gal $10
Effluent pump station LS $1,250,000
Subsurface drip irrigation line LF $10
Irrigation piping & valves LF $250
Imhoff tank LS $1,184,000
Recirculation tank LS $1,320,000
Recirculating gravel filter LS $6,591,000
Plant drainage system ac $40,000
Main generator (including process piping)LS $500,000
Maintenance/operations/electrical building SF $1,000
Phase 1 existing gravity collection system w/ new WWPS & force main LS $17,650,000
Reuse existing Brewer area gravity collection system LS $3,700,000
Phase 2 new gravity collection system w/ new WWPS & force main LS $27,700,000
Sludge dewatering system LS $860,000
Naalehu WWTP
Revised Preliminary Engineering Report
Unit Cost Estimates
Naalehu WWTP Operation, Maintenance, & Replacement Unit Costs Unit Cost Units
Equipment replacement cost 25%of process capital cost
Package plant replacement cost 100%of package plant captial cost
Maintenance materials 2%of equipment capital cost
Gravity mainline collection system maintenance cost $16,000.00 per mi
Force main collection system maintenance cost $10,000.00 per mi
Membrane replacement cost $1,950.00 per module + S&H & install
Solids disposal dumpster rental fee $500.00 per week
Sanitary landfill tipping fee $116.00 per wet ton
Hypochlorite tablet cost $8.00 per lb
Dewatering polymer cost $3.00 per lb
Diesel price $6.06 per gallon
Naalehu WWTP
Revised Preliminary Engineering Report
Lump Sum Cost Estimates
Imhoff Tank Units Unit Cost Number of Units Cost
Excavation CY $300 450 $135,000
Bedding & backfill CY $100 35 $3,500
Concrete CY $1,500 160 $240,000
Piping & valves LS $50,000 1 $50,000
Cover plates SF $200 75 $15,000
Odor control LS $500,000 1 $500,000
Epoxy Coating SF $80 3,000 $240,000
$1,184,000
Recirculating Gravel Filter Units Unit Cost Number of Units Cost
RGF bed excavation CY $300 11,800 $3,540,000
Bed liner SF $8 75,100 $600,800
20-inch PVC manifold pipe LF $200 400 $80,000
3-inch PVC lateral pipe LF $30 13,900 $417,000
6-inch PVC drainage pipe LF $60 3,700 $222,000
8-inch PVC recirculation pipe LF $80 200 $16,000
Gravel media CY $150 10,500 $1,575,000
6 in sand media under liner CY $100 1,400 $140,000
$6,591,000
Recirculation Tank Units Unit Cost Number of Units Cost
Recirculation tank excavation CY $300 1,480 $444,000
Bedding & backfill CY $100 200 $20,000
Concrete CY $1,500 290 $435,000
Handrail LF $100 210 $21,000
Pumps & valves ea $100,000 4 $400,000
$1,320,000
TOTAL
TOTAL
TOTAL
Naalehu WWTP
Revised Preliminary Engineering Report
Lump Sum Cost Estimates
Sludge Dewatering System Units Unit Cost Number of Units Cost
300 HP diesel dump truck LS $300,000 1 $300,000
Dewatering screw press LS $300,000 1 $300,000
Incline screw conveyor LS $80,000 1 $80,000
Polymer system LS $80,000 1 $80,000
Sludge feed pump & piping LS $100,000 1 $100,000
$860,000
Reuse Existing Gravity Collection System Units Unit Cost Number of Units Cost
Inspection & cleaning LS $1,500,000 1 $1,500,000
Repair defects LS $2,000,000 1 $2,000,000
Archaeological monitoring LS $50,000 1 $50,000
BMPs LS $50,000 1 $50,000
Traffic control measures LS $50,000 1 $50,000
Pre- & post-construction inspections & documentation LS $50,000 1 $50,000
$3,700,000
New Drainage Channel Units Unit Cost Number of Units Cost
Earthwork CY $250 49500 $12,375,000
Concrete culverts LS $1,250,000 1 $1,250,000
Archaeological monitoring LS $25,000 1 $25,000
Clear and grub LS $25,000 1 $25,000
BMPs LS $25,000 1 $25,000
$13,700,000TOTAL
TOTAL
TOTAL
Naalehu WWTP
Revised Preliminary Engineering Report
Cost Estimate
Naalehu WWTP Capital Cost Item Description Units General Unit Cost Number of Units COST
Phase 2 new gravity collection system w/ new WWPS & force main LS $27,700,000 1 $27,700,000
Subtotal $27,700,000
Contingency @ 20%$5,540,000
Engineering, Admin, & Legal @ 25%$6,925,000
Collection System Total $40,165,000
Drainage channel improvements LS $13,700,000 1 $13,700,000
Subtotal $13,700,000
Contingency @ 20%$2,740,000
Engineering, Admin, & Legal @ 25%$3,425,000
Drainage Channel Total $19,865,000
Environmental protection, BMPs ac $11,000 1.5 $16,500
Site clearing ac $20,000 1.5 $30,000
Site roads, guard rails, pavement ac $92,000 1.5 $138,000
Perimeter fence LF $150 4,100 $615,000
WWTP site grading ac $30,000 1.5 $45,000
WWTP site drainage improvements ac $18,000 1.5 $27,000
Plant water catchment/collection system LS $75,000 1 $75,000
Process yard piping LS $250,000 1 $250,000
Headworks (includes site/civil, structures, equipment & piping)LS $1,024,000 1 $1,024,000
Influent pump station LS $1,670,000 1 $1,670,000
Chlorine disinfection LS $150,000 1 $150,000
RAS package plants LS $3,812,000 1 $3,812,000
Plant drainage system ac $40,000 1.5 $60,000
Main generator (including process piping)LS $500,000 1 $500,000
Maintenance/operations/electrical building SF $1,000 2,150 $2,150,000
Sludge dewatering system LS $860,000 1 $860,000
Subtotal $11,422,500
Electrical & Instrumentation @ 25%$2,856,000
Subtotal $14,279,000
Contingency @ 20%$2,856,000
Engineering, Admin, & Legal @ 25%$3,570,000
Wastewater Treatment Total $20,705,000
Irrigation equalization tank gal $10 20,000 $200,000
Effluent pump station LS $1,250,000 1 $1,250,000
Subsurface drip irrigation line LF $10 54,000 $540,000
Irrigation piping & valves LF $250 900 $225,000
Subtotal $2,215,000
Electrical & Instrumentation @ 25%$554,000
Subtotal $2,769,000
Contingency @ 20%$554,000
Engineering, Admin, & Legal @ 25%$693,000
Effluent Disposal Total $4,016,000
Alternative #1 TOTAL $84,751,000
Effluent Disposal
Alternative #1 - RAS Package Plants / Subsurface Drip
Capital Cost Estimate
Wastewater Treatment
Collection System
Drainage Channel
Naalehu WWTP
Revised Preliminary Engineering Report
Cost Estimate
Naalehu WWTP Capital Cost Item Description Units General Unit Cost Number of Units COST
Phase 2 new gravity collection system w/ new WWPS & force main LS $27,700,000 1 $27,700,000
Subtotal $27,700,000
Contingency @ 20%$5,540,000
Engineering, Admin, & Legal @ 25%$6,925,000
Collection System Total $40,165,000
Drainage channel improvements LS $13,700,000 1 $13,700,000
Subtotal $13,700,000
Contingency @ 20%$2,740,000
Engineering, Admin, & Legal @ 25%$3,425,000
Drainage Channel Total $19,865,000
Environmental protection, BMPs ac $11,000 1.5 $16,500
Site clearing ac $20,000 1.5 $30,000
Site roads, guard rails, pavement ac $92,000 1.5 $138,000
Perimeter fence LF $150 4,100 $615,000
WWTP site grading ac $30,000 1.5 $45,000
WWTP site drainage improvements ac $18,000 1.5 $27,000
Plant water catchment/collection system LS $75,000 1 $75,000
Process yard piping LS $250,000 1 $250,000
Headworks (includes site/civil, structures, equipment & piping)LS $1,024,000 1 $1,024,000
Influent pump station LS $1,670,000 1 $1,670,000
Chlorine disinfection LS $150,000 1 $150,000
MBR package plants LS $3,579,000 1 $3,579,000
Plant drainage system ac $40,000 1.5 $60,000
Main generator (including process piping)LS $500,000 1 $500,000
Maintenance/operations/electrical building SF $1,000 2,150 $2,150,000
Sludge dewatering system LS $860,000 1 $860,000
Subtotal $11,189,500
Electrical & Instrumentation @ 25%$2,798,000
Subtotal $13,988,000
Contingency @ 20%$2,798,000
Engineering, Admin, & Legal @ 25%$3,497,000
Wastewater Treatment Total $20,283,000
Irrigation equalization tank gal $10 20,000 $200,000
Effluent pump station LS $1,250,000 1 $1,250,000
Subsurface drip irrigation line LF $10 54,000 $540,000
Irrigation piping & valves LF $250 900 $225,000
Subtotal $2,215,000
Electrical & Instrumentation @ 25%$554,000
Subtotal $2,769,000
Contingency @ 20%$554,000
Engineering, Admin, & Legal @ 25%$693,000
Effluent Disposal Total $4,016,000
Alternative #2 TOTAL $84,329,000
Wastewater Treatment
Effluent Disposal
Alternative #2 - MBR Package Plants / Reuse / Subsurface Drip
Capital Cost Estimate
Collection System
Drainage Channel
Naalehu WWTP
Revised Preliminary Engineering Report
Cost Estimate
Naalehu WWTP Capital Cost Item Description Units General Unit Cost Number of Units COST
Phase 2 new gravity collection system w/ new WWPS & force main LS $27,700,000 1 $27,700,000
Subtotal $27,700,000
Contingency @ 20%$5,540,000
Engineering, Admin, & Legal @ 25%$6,925,000
Collection System Total $40,165,000
Drainage channel improvements LS $13,700,000 1 $13,700,000
Subtotal $13,700,000
Contingency @ 20%$2,740,000
Engineering, Admin, & Legal @ 25%$3,425,000
Drainage Channel Total $19,865,000
Environmental protection, BMPs ac $11,000 2 $22,000
Site clearing ac $20,000 2 $40,000
Site roads, guard rails, pavement ac $92,000 2 $184,000
Perimeter fence LF $150 4,100 $615,000
WWTP site grading ac $30,000 2 $60,000
WWTP site drainage improvements ac $18,000 2 $36,000
Plant water catchment/collection system LS $75,000 1 $75,000
Process yard piping LS $250,000 1 $250,000
Headworks (includes site/civil, structures, equipment & piping)LS $1,024,000 1 $1,024,000
Influent pump station LS $1,670,000 1 $1,670,000
Imhoff tank LS $1,184,000 1 $1,184,000
Recirculation tank LS $1,320,000 1 $1,320,000
Recirculating gravel filter LS $6,591,000 1 $6,591,000
Chlorine disinfection LS $150,000 1 $150,000
Plant drainage system ac $40,000 2 $80,000
Main generator (including process piping)LS $500,000 1 $500,000
Maintenance/operations/electrical building SF $1,000 1,645 $1,645,000
Sludge dewatering system LS $860,000 1 $860,000
Subtotal $16,306,000
Electrical & Instrumentation @ 25%$4,077,000
Subtotal $20,383,000
Contingency @ 20%$4,077,000
Engineering, Admin, & Legal @ 25%$5,096,000
Wastewater Treatment Total $29,556,000
Irrigation equalization tank gal $10 20,000 $200,000
Effluent pump station LS $1,250,000 1 $1,250,000
Subsurface drip irrigation line LF $10 54,000 $540,000
Irrigation piping & valves LF $250 900 $225,000
Subtotal $2,215,000
Electrical & Instrumentation @ 25%$554,000
Subtotal $2,769,000
Contingency @ 20%$554,000
Engineering, Admin, & Legal @ 25%$693,000
Effluent Disposal Total $4,016,000
Alternative #3 TOTAL $93,602,000
Wastewater Treatment
Effluent Disposal
Alternative #3 - Imhoff Tank / RGF / Subsurface Drip
Capital Cost Estimate
Collection System
Drainage Channel
Electricity cost $0.45 /kWh
Flow
ADWF:0.125 mgd
0.193404 cfs
Labor (common across all alternatives)
COH WWTP operator annual salary $100,000 including fringe benefits
Number of employees/operators 3 2 shifts: Wed - Sat / Mon - Fri + 1 supervisor
Annual labor cost:$300,000
Electricity
Equivalent Annual Alt 1 Alt 2 Alt 3
Duty Unit Motor Size Use Continuous Power RAS PP MBR PP RGF
Load Count (hp)Factor Load (hp)(kWh)(kWh)(kWh)(kWh)
Headworks
Screens 1 2 20%0.4 2,613 2,613 2,613 2,613
Grit blower 2 5 100%10 65,323 65,323 65,323 65,323
Process tanks
Anoxic zone mixers 2 5 100%10 65,323 65,323 65,323 N/A
Aeration blower (main)1 27 100%27 176,373 176,373 176,373 N/A
Aeration blower (flow equalization)1 13 100%13 84,920 84,920 84,920 N/A
Imhoff tank odor control 1 2 100%2 13,065 N/A N/A 13,065
Recirculation tank pump 1 5 100%5 32,662 N/A N/A 32,662
Influent pump 1 10 30%3 19,597 19,597 19,597 19,597
Effluent pump 1 15 40%6 39,194 39,194 39,194 39,194
Secondary clarifier
Clarifier mechanisms 2 1 100%2 13,065 13,065 N/A N/A
Membranes
Membrane blower 2 5 30%3 19,597 N/A 19,597 N/A
Permeate pumps 2 5 100%10 65,323 N/A 65,323 N/A
Aerobic digestion
Digester blowers 2 5 90%9 58,791 58,791 58,791 58,791
Sludge dewatering
Screw press feed pump 1 5 30%1.5 9,798 9,798 9,798 9,798
Screw press 1 2 30%0.6 3,919 3,919 3,919 3,919
Cake conveyor 1 2 30%0.6 3,919 3,919 3,919 3,919
Miscellaneous
Drainage return pumps 1 5 10%0.5 3,266 3,266 3,266 3,266
Plant water pumps 1 5 100%5 32,662 32,662 32,662 N/A
Fans 2 1 100%2 13,065 13,065 13,065 13,065
591,829 663,685 265,213
$270,000 $300,000 $120,000
Chemicals
Hypochlorite Tablets
Daily chlorine demand @ ADWF 8.3 lbs/d assuming 8 mg/L dose, 15 min contact time @ PHWWF
Annual hypochlorite demand @ ADWF 3,030 lbs/yr
Hypochlorite tablet unit cost $8 per lb
Total annual hypochlorite tablet cost:$24,300 common across all alternatives
Dewatering polymer
Daily dewatering polymer use 1.7 lbs/d assuming 20 lbs/dry ton dose
Annual dewatering polymer use 621.0 lbs/yr
Dewatering polymer unit cost $3 per lb
Total annual dewatering polymer cost:$1,900 common across all alternatives
Naalehu WWTP
Revised Preliminary Engineering Report
O&M Cost Estimates
Annual electricity consumption kWh:
Annual electricity cost:
Page 1 of 3
MBR cleaning chemicals
Sodium hypochlorite & citric acid cost:$5,000 per yr Alternative #2 only
Membrane replacement (Alt #2)
Membrane cost per module $1,950 material costs only
Estimated additional costs per module $550 shipping & handling + installation costs
Number of membrane modules 24 modules (12 per unit)
Membrance replacement cost (15 year):$60,000
WWTP maintenance materials
Alt 1 Alt 2 Alt 3
RAS PP MBR PP RGF
Package plant capital cost $3,812,000 $3,579,000 N/A
Process equipment capital cost $8,104,000 $8,104,000 $16,694,000 not including package plant
Equipment replacement cost factor 25.0%25.0%25.0%replace after 20 years
process equipment replacement cost $2,026,000 $2,026,000 $4,173,500 not including package plants
Total WWTP equipment replacement cost:$5,838,000 $5,605,000 $4,174,000 includes 100% package plant replacement
Maintenance materials cost factor 2.0%2.0%2.0%
Total WWTP annual maintenance materials cost:$117,000 $113,000 $84,000
Sludge disposal
Daily dewatering flow:680 gpd
Daily dewatered sludge mass 0.71 wet tons/d
West HI sanitary landfill tipping fee $116.00 per wet ton
Onsite disposal roll off dumpster size 10 cu yds
Dumpster rental fee $500.00 per week
Annual dumpster rental fee $26,000.00
Disposal frequency 7 days Requires weekly disposal (once every 7 days)
Diesel price (dollar per gallon)$6.06 per gallon
Employee labor cost per hour $48.08 per hour based on 100K annual salary
Distance Naalehu to Landfill (roundtrip)165 mi
Dump truck fuel economy 5.0 mpg
Annual sludge disposal cost (truck to landfill)
Annual fuel cost $10,400
Annual landfill tipping fee $30,000
Annual Dumpster rental fee $26,000
Total annual sludge disposal cost:$67,000
Collection system
Phase 1: Reuse Brewer gravity collection system (Close LCCs) maintenance
Existing Brewer gravity sewer mainline 20,788 ft 2004 Kau Sewer System Evaluation Report
3.94 mi
Existing gravity mainline multiplier 3
Gravity mainline maintenance cost $48,000
Annual mainline maintenance cost:$188,990
New gravity sewer mainline (FM to WWTP)2,500 ft
New gravity sewer mainline (LCCs to SPS)1,950 ft
New gravity sewer mainline TOTAL 4,450 ft
0.84 mi
Gravity mainline maintenance cost $16,000 per mi
Annual gravity mainline maintenance cost:$13,490
Force main length 2,800 ft Fukunaga estimate
0.53 mi
Force main maintenance cost $10,000 per mi
Annual force main maintenance cost:$5,310
WWPS process equipment capital cost $1,670,000 Assume equal to influent pump station
WWPS process equipment replacement cost:$400,000 20 year replacement
Total annual maintenance materials cost:$10,000
Total annual WWPS electricity cost $20,000
Total annual maintenance cost:$238,000
Page 2 of 3
Phase 2: New Brewer gravity collection system maintenance
New Brewer gravity sewer mainline 10,140 ft
New gravity sewer mainline (FM to WWTP)2,500 ft
New gravity sewer mainline TOTAL 12,640 ft
2.39 mi
Gravity mainline maintenance cost $16,000 per mi
Annual gravity mainline maintenance cost:$38,310
Force main length 2,800 ft Fukunaga estimate
0.53 mi
Force main maintenance cost $10,000 per mi
Annual force main maintenance cost:$5,310
WWPS process equipment capital cost $1,670,000 Assume equal to influent pump station
WWPS process equipment replacement cost:$400,000 20 year replacement
Total annual maintenance materials cost:$10,000
Total annual WWPS electricity cost $20,000
Total annual maintenance cost:$74,000
Page 3 of 3
County of Hawaii
Naalehu WWTP Revised PER
Alternatives Net Present Value Analysis
Agency: County of Hawaii Sensitivity Adjustments (%)Results
Project/Problem: Naalehu Collection System Risk
Premium Benefits Capital
Costs
Other
Costs Capital Cost 30-year
NPV
Alternative 1 Phase 1 - Reuse C Brewer Collection System $30,032,500 ($35,930,046)
Alternative 2 Phase 2 - New C Brewer Collection System $40,165,000 ($42,197,986)
Alternative 3
Alternative 4
Alternative 5
Year of analysis: 2023 Note: "Status quo" refers to
Escalation rate: 3.50% Alternative 1
Discount rate: 5.00%
Make entries in yellow cells only
All entries in dollars
All entries in thousands of dollars
Select one
County of Hawaii
Naalehu WWTP Revised PER
Alternatives Net Present Value Analysis
Agency: County of Hawaii Sensitivity Adjustments (%)Results
Project/Problem: Naalehu Disinfection System Risk
Premium Benefits Capital
Costs
Other
Costs Capital Cost 30-year
NPV
Alternative 1 Tablet Chlorination Feed System $150,000 ($738,500)
Alternative 2 Ultraviolet Light (UV) System $1,100,000 ($1,335,400)
Alternative 3
Alternative 4
Alternative 5
Year of analysis: 2023 Note: "Status quo" refers to
Escalation rate: 3.50% Alternative 1
Discount rate: 5.00%
Make entries in yellow cells only
All entries in dollars
All entries in thousands of dollars
Select one
County of Hawaii
Naalehu WWTP Revised PER
Alternatives Net Present Value Analysis
Agency: County of Hawaii Sensitivity Adjustments (%)Results
Project/Problem: Naalehu WWTP Revised PER Risk
Premium Benefits Capital
Costs
Other
Costs Capital Cost 30-year
NPV
Alternative 1 RAS Package Plants / Subsurface Drip $84,751,000 ($109,555,755)
Alternative 2 MBR Package Plants / Subsurface Drip $84,329,000 ($109,776,643)
Alternative 3 Imhoff Tank / RGF / Subsurface Drip $93,602,000 ($112,851,053)
Alternative 4
Alternative 5
Year of analysis: 2023 Note: "Status quo" refers to
Escalation rate: 3.50% Alternative 1
Discount rate: 5.00%
Make entries in yellow cells only
All entries in dollars
All entries in thousands of dollars
Select one
County of Hawaii DEM
Naalehu Revised AOC PER
Alternatives Net Present Value Analysis
Agency: County of Hawaii DEM Sensitivity Adjustments (%)Results
Project/Problem: Naalehu Revised AOC PER Risk
Premium Benefits Capital
Costs
Other
Costs Capital Cost 30-year
NPV
Alternative 1 i. Package plant and new collection system $84,329,000 ($109,776,643)
Alternative 2 ii. Package plant connected to existing collection system $74,197,000 ($103,505,201)
Alternative 3 IWS management model 2A $29,100,000 ($38,859,287)
Alternative 4 iii. A maintenance contract model IWS program $29,100,000 ($39,321,375)
Alternative 5 IWS management model 3A $29,100,000 ($39,093,038)
Alternative 6 iv. An operating permit model IWS program $29,100,000 ($41,422,061)
Alternative 7
Alternative 8
Alternative 9
Alternative 10
Alternative 11
Alternative 12
Year of analysis: 2023 Note: "Status quo" refers to
Escalation rate: 3.50% Alternative 1
Discount rate: 5.00%
Make entries in yellow cells only
All entries in dollars
All entries in thousands of dollars
Select one
Naalehu WWTP Revised PER
B
Appendix B: Letter to Support Department of Hawaii
Flow Variance Application
2261 Aupuni Street, Suite 201
Wailuku, Maui, HI 96793
T: 808.244.7005
July 18, 2023
Mr. Mark Grant
County of Hawaii Wastewater Division
108 Railroad Ave
Hilo, HI 96729-4252
Subject: Naalehu Wastewater Treatment Plant – Capacity Phasing
Dear Mr. Grant,
The County of Hawaii (County) is investigating options to reduce the size and impact of
the Naalehu Wastewater Treatment Plant (WWTP). While previous planning and design
efforts focused on an aerated lagoon secondary WWTP, the County is now evaluating a
mechanical secondary treatment process to strive to meet the EPA Administrative Order
on Consent (AOC) deadlines.
This letter provides information regarding a phased capacity innovative approach to the
project scope that will further the County’s goals. A phased WWTP capacity approach
will require Department of Health (DOH) acceptance as it potentially falls outside of nor-
mally accepted practices and regulatory guidance.
Phased WWTP capacity implementation is proposed to reduce initial WWTP size while
protecting human health and the environment. The phasing approach that the County is
proposing requires an explanation of deviations from Hawaii Administrative Rules (HAR)
11-62, including utilization of potable water use data to estimate wastewater flows,
peak flow prediction, and phasing implementation.
1.1 Background
HAR 11-62 requires WWTPs to be designed in accordance with County standards, or the
City and County of Honolulu (CCH) standards if no applicable County standards exist.
The County does not have its own WWTP standards, and therefore relies on the CCH
standards.
Project planning and design to date has followed the CCH flow standards that were up-
dated in 2017. Table 1 provides a summary of the flows to the Naalehu WWTP based
on the 2017 CCH standards.
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 2
Table 1. Naalehu WWTP Flows Based on 2017 CCH Standards
Description Peaking Factor Value
Average dry weather flow 1.0 225,000 gpd
Peak day dry weather flow 2.0 446,000 gpd
Peak day wet weather flow a 2.5 563,000 gpd
Peak hour wet weather flow 3.1 480 gpm
(691,000 gpd)
Notes: gpd = gallons per day, gpm = gallons per minute
a Peak day wet weather flow is not part of the CCH standards but is an important WWTP design parameter.
Peak day wet weather flow estimate was developed using an appropriate peaking factor.
The 2017 CCH flow standards include three elements:
1. Wastewater flow generation estimates based on equivalent population esti-
mates (70 gallons per capita per day (gpcd)). This reflects the amount of
wastewater that is expected to enter the sewer from residences and businesses
and provide the main source of organic material mass to be removed by the
WWTP process.
2. Dry weather infiltration and inflow (I/I) estimates based on equivalent population
estimates (35 gpcd).
3. Wet weather I/I estimates based on service area acreage (3,000 gallons per
acre per day (gpad)).
1.2 County Experience with the CCH Flow Standards
The CCH standards were established for a major metropolitan area that includes vast
areas of residential, commercial, and industrial development, with significant propor-
tions of service areas near sea level elevations. Wastewater generation rates are gener-
ally lower in rural areas than in urban areas. Typical flow rates in the United States
range between 50 gpcd in rural areas and 120 gpcd in typical urban areas
(Tchobanoglous, George, F. L. Burton, and H.D. Stensel, Wastewater Engineering: Treat-
ment and Reuse / Metcalf & Eddy, Inc., 4th edition, 2003). The County’s experience with
the CCH flow standards on other projects (e.g., Honokaa WWTP) has illustrated that the
standards are very conservative for small rural communities located at higher elevations
on Hawaii Island. The observed monthly average dry weather flows at Honokaa are con-
sistently less than 50 percent of the average dry weather flow design capacity of the
WWTP. Peak day wet weather flow events have been near the WWTP facility capacity as
designed per the 1993 CCH standards that were in effect at the time (1,250 gpad for
sewers above the water table). Therefore, the current wastewater standards based on
urban Honolulu are likely overly conservative for rural communities like Naalehu, as sub-
stantiated by flows observed at Honokaa WWTP and discussed in Section 1.5.
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 3
1.3 Service Area
Fukunaga & Associates, Inc (FAI) prepared a preliminary engineering report for the
Naalehu wastewater collection system improvements in May 2020. The results of FAI’s
investigation established an updated service area for the proposed Naalehu WWTP that
incorporates both the town’s and County’s needs. Figure 1 shows the updated WWTP
service area, which includes properties that are currently connected to the three large
capacity cesspools (LCC 3, 4, and 5), and properties that will be “newly accessible” to
the collection system after the replacement collection system is constructed. LCC 1 and
2 are located in the neighboring town of Pahala.
Figure 1. Naalehu WWTP Service Area Established by Fukunaga & Associates, Inc
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 4
Table 2 provides a summary of the WWTP service area.
Table 2. Naalehu WWTP Service Area Summary
Property Type Number of Parcels
Existing C Brewer Lots Newly Accessible Lots New Collection Total
Residential 159 25 184
Commercial 2 7 9
Church 1 1 2
Industrial - 2 2
Agricultural 1 2 3
Residential/Commercial 1 1 2
Residential/Agricultural - 1 1
Park - 1 1
Total 164 40 204
1.4 Potable Water Use
The amount of wastewater generated within a residence will not exceed the amount of
potable water used by the occupants. Therefore, potable water use records can be used
to estimate wastewater generation rates within existing communities where no com-
bined sewers are present. The County of Hawaii Department of Water Supply (DWS) pro-
vided potable water use records for the parcels located within the service area from No-
vember 2017 through October 2022. Figure 2 provides an analysis of the potable water
use records, with adjustments for properties for which no water use data was available.
As shown figure 2, the maximum monthly average water use during the period of record
was approximately 78,000 gpd in May and June 2018.
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 5
Figure 2. Average Potable Water Use in Naalehu WWTP Service Area, Nov 2017 – Oct 2022
Potable water is used both indoors and outdoors in residential areas, but only indoor
uses enter the sewer system. Figure 3 shows the results of an irrigation demand analy-
sis for Naalehu. Peak irrigation demands occur during the months of May through Au-
gust, but inspection of potable water demands in Figure 2 shows little to no increase in
potable water use during the driest months of the year. Therefore, it is reasonable to
conclude that Naalehu residents do not use significant volumes of potable water for out-
door irrigation purposes, and most of the potable water that is supplied to the commu-
nity by DWS ends up in the sewer.
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecBilled Water (gpd)2017 2018 2019 2020 2021 2022
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 6
Figure 3. Naalehu Irrigation Analysis
Based on the above analyses, we believe assuming an 80,000 gpd monthly average
wastewater generation rate in the capacity calculations reflect the current needs of the
service area.
Daily wastewater flows can vary substantially from the monthly average flow. The CCH
standards use a 2.5 peaking factor to estimate the maximum wastewater flow into the
collection system. The 2.5 peaking factor is appropriate for Naalehu, resulting in a maxi-
mum wastewater flow of 200,000 gpd.
1.5 Dry Weather I/I Allowance
Groundwater can infiltrate into wastewater collection systems during dry weather, in-
creasing the flow to the WWTP. The 2017 CCH standards specify a dry weather I/I allow-
ance of 35 gpcd. The previous CCH standards (dated 1993) specified a dry weather I/I
allowance of 5 gpcd for properties located above the groundwater table. The significant
increase in the dry weather I/I allowance in the latest CCH standard will help the CCH to
plan for increased dry weather I/I due to sea level rise effects in Honolulu. The Honokaa
WWTP was designed for an average dry weather flow (ADWF) capacity of 200,000 gpd,
which includes a dry weather I/I allowance based on the 1993 CCH standards. The
County’s experience at Honokaa has been that the 1993 dry weather I/I allowance is ad-
equate for a rural collection system located in Hawaii Island’s well-drained geology, at
elevations hundreds of feet above sea level, and a significant distance from the shore-
line. Figure 4 summarizes annual average effluent flows at the Honokaa WWTP, which
include dry weather I/I. The high flows in July 2016 and August 2018 were due to Hurri-
canes Darby and Lane, respectively. We conclude that continued use of the 1993
0
1000
2000
3000
4000
5000
6000
0
1
2
3
4
5
6
7
8
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Irrigation Demand (gal/ac-day)Precipitation and Evapotranspiration (in)Precipitation Evapotranspiration Irrigation Demand
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 7
standard for dry weather I/I is appropriate for Naalehu and using the 2017 standard
would be overly-conservative.
Figure 4. Honokaa WWTP Monthly Average Effluent Flows, Apr 2016 – Apr 2021
1.6 Wet Weather I/I Allowance
The 2017 CCH standards, which specify a wet weather I/I allowance of 3,000 gpad, are
used for all wet weather I/I calculations.
1.7 Phased Capacity Implementation Recommendations
A phased approach towards implementing WWTP capacity is recommended to provide a
flexible and appropriately sized wastewater treatment and disposal facility for the
Naalehu community:
· Phase 1: Provide sufficient capacity for the existing parcels within the service
area, including newly accessible parcels, reflecting current development. This
will allow the County to close the LCCs. Provide sufficient area within the WWTP
site for future expansion.
· Phase 2: When needed, expand the WWTP capacity to reflect the full CCH flow
standards requirements for the existing service area. HAR 11-62 requires devel-
opment of a facility plan when flows reach 75 percent of capacity and implemen-
tation of capacity-increasing measures at 90 percent.
· Phase 3: When needed, expand the WWTP capacity to reflect the recommenda-
tions included in the Kau Community Development Plan to sewer the entire com-
munity. This is not anticipated to occur within the near future and is not part of
the current project’s environmental assessment.
0
50,000
100,000
150,000
200,000
250,000
Apr 2016 Apr 2017 Apr 2018 Apr 2019 Apr 2020 Apr 2021Monthly average effluent flow (gpd)Effluent Flow (gpd)WWTP ADWF Capacity (gpd)
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 8
Table 3 provides a summary of the calculated capacities for the three-phase approach.
Table 3. Calculated Capacity Phasing
Description Phase 1 Phase 2 Phase 3
Base sanitary flow 80,000 gpd 147,000 gpd 211,000 gpd
Peak base sanitary flow a 200,000 gpd 368,000 gpd 528,000 gpd
Dry weather I/I b 12,000 gpd 78,000 gpd 119,000 gpd
Wet weather I/I c 245,000 gpd 245,000 gpd 931,000 gpd
Average dry weather flow d 92,000 gpd 225,000 gpd 330,000 gpd
Peak day dry weather flow e 212,000 gpd 446,000 gpd 647,000 gpd
Peak day wet weather flow f 322,000 gpd
PF=3.5
563,000 gpd
PF=2.5
825,000 gpd
PF=2.5
Peak hour wet weather flow h 317 gpm
(457,000 gpd)
480 gpm
(691,000 gpd)
1096 gpm
(1,578,000 gpd)
a Base sanitary flow x 2.5 peaking factor.
b 5 gpcd for Phase 1, 35 gpcd for Phase 2 and Phase 3.
c 3,000 gpad
d Base sanitary flow + dry weather I/I.
e Peak base sanitary flow + dry weather I/I.
f Average dry weather flow x peaking factor (PF) shown. Peak day wet weather flow estimate was developed
using an appropriate peaking factor.
h Peak base sanitary flow + dry weather I/I + wet weather I/I.
HAR 11-62-23.1(i) requires the initiation of a facility planning process when the actual
wastewater flows reach 75 percent of the design capacity of the WWTP, and implemen-
tation of the facility plan must be initiated when actual wastewater flows reach 90 per-
cent of the design capacity. We recommend the Phase 1 WWTP be rated to treat an av-
erage dry weather flow of 125,000 gpd to avoid the potential of having to initiate a
facility plan shortly after the project is constructed. The peak day and peak hour flow ca-
pacities can remain as shown in Table 3. Note that the biological processes in the me-
chanical WWTP will need to be sized to treat the peak day dry weather flow of 212,000
gpd, not the average dry weather flow.
Per capita wastewater generation rate estimates were considered to check the validity
of the proposed Phase 1 average dry weather flow capacity. The non-residential proper-
ties in the service area are expected to contribute approximately 50 percent of the total
flows. Therefore, 50 percent of the average dry weather flow capacity can be allocated
to the residential properties in the service area (92,000 gpd x 50% = 46,000 gpd). If we
consider only the 184 residential properties in the service area, and assume four resi-
dents per residential lot, we have a total residential population of 736 persons (184 lots
x 4 persons/lot = 736 persons). Dividing the residential flow capacity by the population
yields a wastewater flow capacity of approximately 63 gpcd (46,000 gpd / 736 capita =
63 gpcd), which is within the typical values presented in Section 1.2 above.
Mr. Mark Grant
County of Hawaii Wastewater Division
July 18, 2023
Page 9
The proposed Phase 1 capacity is based on actual water use data to establish
wastewater generation rates, and rational assumptions to establish dry weather I/I al-
lowances, and we believe it is appropriate for the Phase 1 existing conditions, while
providing limited capacity for growth. Table 4 presents the recommended Phase 1 ca-
pacity.
Table 4. Recommended Phase 1 Capacity
Description Value Peaking Factor
Average dry weather flow 125,000 gpd 1.0
Peak day dry weather flow 212,000 gpd 1.7
Peak day wet weather flow 322,000 gpd 2.6
Peak hour wet weather flow 457,000 gpd
(317 gpm) 3.7
If the County pursues a WWTP approach (using the Phase 1 capacity recommendation
above) to close the LCCs then a DOH variance from HAR 11-62 requirements will be
needed. The variance will need to be renewed every five years. The WWTP capacity
needs should be re-evaluated upon application for the variance renewal.
Please call me at (808) 442-3301 if you have any questions.
Very truly yours,
Brown and Caldwell
Craig Lekven, P.E.
Project Manager
Naalehu WWTP Revised PER
C
Appendix C: Non-Economic Evaluation
Naalehu WWTP Alternative Solutions
Non-Economic Evaluation July 2023
Category Category Criteria Criteria
Weight Weight
Effluent quality 30% 3 5 3 0.90 1.50 0.90
Potential for capacity expansion 20% 5 5 2 1.00 1.00 0.40
Water recycling feasibility 30% 3 5 2 0.90 1.50 0.60
Public perception / community concerns 20% 3 5 3 0.60 1.00 0.60
Monitoring complexity 25% 4 3 5 1.00 0.75 1.25
Treatment adjustment potential 25% 5 5 3 1.25 1.25 0.75
Safety regulations complexity 25% 4 4 4 1.00 1.00 1.00
Environmental concerns 25% 4 5 3 1.00 1.25 0.75
Footprint 30% 5 5 2 1.50 1.50 0.60
Safe work environment 25% 4 3 4 1.00 0.75 1.00
Maintenance complexity 25% 4 3 4 1.00 0.75 1.00
Operations complexity 20% 4 3 5 0.80 0.60 1.00
Mainland delivery dependence 25% 3 3 4 0.75 0.75 1.00
Mainland servicing dependence 25% 3 3 4 0.75 0.75 1.00
Power dependence 25% 3 3 5 0.75 0.75 1.25
Chemical dependence 25% 4 3 4 1.00 0.75 1.00
***Note : 5 = high/desirable, 1 = low/not-desirable Overall Score: 3.80 3.96 3.53
Alt #3
RGF
Alt #1
RAS
Raw Scores Weighted Scores
Alt #1
RAS
Alt #3
RGF
Alt #2
MBR
Alt #2
MBR
Island Factors 25%
Level of Service 25%
Regulatory 25%
O&M Factors 25%
Naalehu WWTP Revised PER
D
Appendix D: Naalehu Wastewater Collection System
Improvements Technical Memorandum
Fukunaga & Associates, Inc., May 2020
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 2
2. GENERAL CRITERIA
The COH will be the owner of the collection system; therefore, the sewer system will meet COH
standards and be accessible for maintenance. Preference is to construct sewers within the County
ROW as much as possible unless other factors make placing the pipes within easements on private
property or in the State ROW much more practical from economic and engineering standpoints. The
COH prefers sewers not be within easements due to future access challenges when maintenance and
repairs are needed. It is also recommended that the collection system not be located in a State ROW if
possible due to the lengthy review and approval time needed for the Use and Occupancy Agreement
(UOA). This was emphasized by the State Department of Transportation Highways Division (DOT-
H) in their Environmental Assessment (EA) pre-consultation comment to stay out of the State ROW
unless there is no other feasible means of routing the sewer. The collection system will require a
crossing of the State ROW to convey the sewage from the community Mauka of the highway to the
WWTP site that is Makai of the highway; however, DOT-H tends to take less time when reviewing
ROW crossings, especially if they are done using trenchless installation techniques.
3. TOPOGRAPHY
The topography of the Naalehu area is presented in Figure 2. The proposed location of the
wastewater treatment plant is upgradient of the lowest of the former Brewer properties. The ground
elevation of the WWTP site is approximately 690 ft MSL while the ground elevation of the lowest
Brewer house lot is about 645 ft MSL, an elevation difference of 45 feet. A gravity sewer at this depth
is technologically possible using micro tunneling techniques for construction; however, a wastewater
pump station will be more feasible to convey the wastewater to the WWTP due to the cost of micro
tunneling a relatively short distance. The micro tunneling option can be investigated in the event that
an acceptable wastewater pump station location cannot be found.
4. POTENTIAL WASTEWATER PUMP STATION LOCATIONS
As noted in the previous section, the former Brewer properties in Naalehu would most likely be
served by a pump station due to the topography. When investigating potential sites for a wastewater
pump station (WWPS), priority was placed on sites that are on County or State lands to minimize
land acquisition issues, or large private parcels where a portion can be purchased by the County in
hopes of minimizing impact to the landowner. The potential WWPS sites are listed in Table 1, and
shown on Figure 3.
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 3
Table 1: Potential WWPS Sites
TMK Owner Current
Use
Class Size
(sq ft)
Notes
9-5-008:012 Chinese
Society
Church
Church Agricultural 186,001 Requires land from the owner and/or
easement for WWPS site, utilities and road.
Requires sewer and force main in State
ROW.
WWPS can be set back away from houses.
Located at lowest point of the collection
system.
Within 550 feet of school property line.
Longest distance for transmission to
proposed WWTP location.
9-5-008:048 Kuahiwi
Contractors
Inc.
Storage/
Baseyard
Agricultural 534,307 Requires land from the owner and/or
easement for WWPS site, utilities and road.
WWPS can be set back away from most
residents.
Within 300 feet of school property line.
Located near lowest point of the collection
system requiring approx. 15 foot wet well.
9-5-009:006 State of
Hawaii
Naalehu
School
Residential 534,481 Site is frequented by the public.
Residents have indicated sensitivity to
wastewater facility at a school.
Located at lowest point of the collection
system.
9-5-021:023 County of
Hawaii
Naalehu
Park
Residential 279,176 Site is frequented by the public.
Residents may be sensitive to wastewater
facility at a park.
Requires sewer in State ROW.
Located upgradient of some of the former
Brewer properties.
9-5-021:035 Thy Word
Ministries
– Waikoloa
Faith Ctr
Vacant Residential 134,949 Requires land acquisition from the owner
and access easement or dedicated County
road.
Routing would most likely have sewer
within State ROW.
WWPS can be set back away from most
houses.
9-5-024:007 ‘O Ka’u
Kakou Inc.
Senior
Center
Residential/
Commercial
84,680 Facility currently in construction, timing to
coordinate location could be difficult.
Residents may be sensitive to wastewater
facility within senior center campus.
9-5-024:011 County of
Hawaii
LCC
Location
Residential 10,347 Site is surrounded by houses.
Facilities will be relatively close to property
line.
Residents may be sensitive to wastewater
facility in residential area.
Located up-gradient of the lowest Brewer
properties requiring 30+ foot deep wet well.
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 4
Two of the potential sites appear to be more favorable than the others, the County site located within
the former Brewer house lots (TMK 9-5-024:011) and the Kuahiwi Contractors site (TMK 9-5-
008:048). The remaining parcels were eliminated from consideration at this time but can be re-visited
in the future if needed. The Naalehu School and Naalehu Park sites would likely face the most public
opposition due to proximity to areas frequented by the general population for recreation and
education. The Chinese Society Church and Thy Word Ministries sites would require land acquisition
after negotiation with the landowner and a UOA within the State ROW. Both processes would be
time consuming and the land acquisition depends on the landowner’s willingness to cede some of
their land to the County. The new senior center parcel is currently in construction, making the timing
to negotiate the WWPS site difficult and may possibly incur construction delays that would also
factor into the land negotiations.
A. Pump Station on County Parcel TMK 9-5-024:011
The County site would be the most favorable from a timing standpoint. It does not require land
acquisition and would minimize work in the State ROW by limiting construction to a single
crossing of Mamalahoa Highway. However, since this site is up-gradient from the collection
system low point, this site will require deeper sewers and a very deep pump station wet well.
Construction on this site would be more challenging due to the narrow site and the existing
sewers and LCC that would have to remain in operation until the collection system and WWTP
are completed. These utilities, especially the existing sewer pipes, would have to be protected
during construction as heavy vehicles and machinery enter and leave the site. The condition of the
existing pipes may require additional protection such as supplemental concrete cover and/or
partial replacement depending on condition. A proposed layout of a pump station on the County
parcel is shown in Figure 4.
The need to trench for the deep influent sewer and the deep wet well may result in flow from the
LCC being diverted to these trenches due to the lower resistance to flow through the ground to
those excavated areas. Using mud walls for groundwater control would hinder the flow of sewage
from the LCC into the ground and probably reduce the capacity of the LCC. Therefore, septage
pumping for the duration of the pump station construction would most likely be required until the
collection system and WWTP are complete. This would be a significant cost to the construction.
In addition, should there be unforeseen delays in completion of the collection system and/or
WWTP, the additional septage handling due to the delay could result in a significant construction
change order for the additional pumping.
The on-site stormwater may be more difficult to contain due to the small area. Pervious
pavement, if geotechnical investigation shows this type of pavement is permissible, would be
used to minimize hard surfaces on the site. The only hard pavement area required would be the
area designated for refueling of the generator. The grade of the site would be adjusted to
minimize flow of off-site stormwater. Grade adjustment walls are anticipated along the property
lines on the south and west sides of the parcel to raise the ground elevation.
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 5
This site is surrounded by residences directly adjacent to the property line on the east, south and
west. The north side is bordered by Opukea Street. Due to the narrow site, the house structures
are only about 60 feet from the proposed pump station location. The ambient noise from odor
control ventilation fans and electrical switches could be a nuisance to the residents if not
mitigated. The standby generator would also produce noise during testing and operation. This
would require additional sound insulation for the generator and other equipment on the site.
A passive odor control system can be used to eliminate the need for a mechanical fan; however,
passive systems rely on the collection system to be at a higher pressure than atmosphere to force
the foul air through the odor control system. When the collection system becomes pressurized,
odors can begin to leak out of the wet well hatches and nearby manholes so they must also be
gasketed or sealed. A forced-air odor control system using a mechanical fan to draw air out of the
pump station would keep the wet well and collection system at negative pressure, thus
minimizing the chance that odors escape from nearby manholes and hatches.
Electrical and water utilities are located just off-site on Opukea Road. The HELCo transformer
for the site can be located within an easement just off the County road. Water for fire protection
could be from existing hydrants (pending analysis by a fire protection engineer). Water service is
anticipated to be similar to a residential unit to provide wash down and general housekeeping
hose bibbs.
This site poses several risks during construction that could add significantly to the cost and time
to construct the pump station. The site is also narrow and cannot be configured optimally to
mitigate noise, which could be significant to the homeowners directly adjacent to the site.
B. Pump Station on Portion of Kuahiwi Contractors, Inc. Parcel TMK 9-5-008:048
The Kuahiwi Contractors site is private property and would require time to negotiate the
subdivision or easement for the WWPS site and access roadway; however, similar to the County
site, work in the State ROW can be limited to a single crossing of the highway. The anticipated
size of the site is about 8000 to 9000 square feet. A proposed pump station layout and site are
presented in Figure 5. A larger area may be needed if soil conditions require a larger area to
mitigate on-site stormwater flows. This is smaller than the County parcel above but the
dimensions can be optimized to provide the area needed for the facility. This site is located at the
low point of the collection system, which would keep the sewers and pump station wet well at
more typical depths. Locating the WWPS on a portion of the Kuahiwi Contractors site would
allow sewering of the Iglesia ni Cristo Church that requested connection but will place it at the
farthest point from the WWTP, thus increasing the force main and sewer lengths required. An
access road or driveway would also be needed to the site. A gravel drive would minimize the
impervious surface area but can be susceptible to erosion during heavy rains.
The pump station would be placed close to the south property line, the low side of the parcel. The
far south east or Hilo corner of the parcel is the lowest point where stormwater from this parcel
and possibly some adjacent parcels collect before entering a drainage culvert under Mamalahoa
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 6
Highway. Anecdotal reports from residents indicate the highway floods at the storm drain during
heavy or sustained rains. There is also a swale that appears to divert stormwater from cattle and
horse pens on the site toward the far south east corner. It is recommended that the County not
encroach into the far south east corner to maintain the current storm drainage pattern from the
site. An aerial view of the area is shown in Figure 6. On-site stormwater can be contained by
making the site large enough for impoundments and by using pervious pavement where possible
depending on geotechnical investigation data. The only road area requiring hard surfacing is the
area designated for re-fueling the generator. Grade adjustment walls are anticipated along the
perimeter of the pump station site to raise the grade on the south side and lower the grade on the
north side to even out the elevation of the site and minimize inflow of off-site storm water.
The site would be bordered on the south by residences unless the pump station is moved further
interior of the parcel. If the pump station site is located against the south property line, the pump
station could be as close as 80 feet from the house structures. Similar to the County parcel, the
ambient noise from equipment could be a nuisance to the residents if not mitigated. This parcel
would allow the County to obtain a more optimally configured site that would allow an additional
motor control center (MCC) room that would not only mitigate noise issues from electrical
switches, but also allow the valuable electrical equipment to be secured in a locked room. The
MCC room can be integrated into the generator building. Noise from the odor control system
could also be an issue, especially from the fan that would operate continuously. However, the site
can be optimally sized to allow sound attenuating enclosures around the fan or around the entire
odor control system. Therefore, a passive odor control system as discussed above for the County
parcel site is probably not needed at this site.
Running electrical utility and communication lines would be more costly for this site since the
closest pole would be on Ohai Road. HELCo would charge the County to run utility lines to their
transformer near the pump station site. As an alternative, the HELCo transformer and meter can
be placed within an easement near Ohai Road and the County would own the power lines going
into the site. This option is mentioned in case HELCo prefers not to own the power lines going
into the site or requires road improvements that would not be favorable to the County. This would
require discussion with and approval by HELCo and would have to be analyzed further by an
electrical engineer.
A potable water line would be required at the site for wash down and general housekeeping. In
addition, a hydrant for fire protection would be needed. The potable water pipe in Naalehu appear
to be 6-inch diameter. The new potable water line to the site would maintain the 6-inch size to
maximize the water flow in case of fire or other emergency requiring water.
This site is preferred from an engineering standpoint because it is at the low side of the collection
system and does not entail unknowns during construction such as breakage of existing utilities or
need for septage pumping for unknown duration. It can also be optimally configured to mitigate
noise and odors.
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 7
5 COLLECTION SYSTEM DESIGN
The town of Naalehu is divided by a concrete flood control canal into an east side (Hilo side) where
the majority of the properties are residences, and a west side (Kona side) where the majority of the
properties are commercial. The town is also divided in the Mauka (mountain) and Makai (ocean)
directions by the Mamalahoa Highway. The collection system will convey the wastewater to the
proposed WWTP that is located on the Makai-Kona side of Naalehu. The Naalehu collection system
will be analyzed as two distinct systems, one serving the former Brewer house lots located on the
Mauka-Hilo side to allow closure of the LCCs, and the gravity sewer located on the Kona side to
transport the sewage to the proposed WWTP. An added benefit would be provision of sewer service
to the two restaurants requesting connection. The church on the Hilo side that requested service falls
outside of this area. The County has expressed a desire to accommodate their request; however,
depending on the location of the WWPS, connection of the church may have to be deferred.
C. Former Brewer House Lots
The former Brewer house lots are located on the Mauka-Hilo side as shown in Figure 7. The
houses are on a hillside with a slope of 8% to 9%, ranging in elevation from about 780 ft MSL to
645 ft MSL. The steep hillside results in houses located on the downhill side of the street being
below the elevation of the street. Sewage from houses on the uphill side can flow easily by
gravity to a sewer in the street. On the downhill side; however, the lateral serving the home is
lower than a typical depth sewer (typically designed with 4 feet to 5 feet cover). Four options
were investigated to address the low-lying properties; use of easements on private property,
vacuum sewers, individual grinder pump stations at low-lying properties, and deep sewers to
allow gravity flow from the low-lying properties.
i. Easements
The use of easements was eliminated as a viable option at this time. An initial investigation of
the house lots along the backyard property lines where an easement would be most beneficial
revealed extensive homeowner improvements. As part of sewer construction and easement
terms, the improvements can be removed and the homeowners can be ordered to keep
improvements off of the easements. However, over time it is likely that the homeowners’
memory of the easement locations would fade and various improvements may be placed over
the easement, hindering access by the County for repairs and maintenance.
ii. Vacuum Sewers
The use of vacuum sewers was also eliminated at this time. Vacuum sewers use a sealed
sewer system that produces suction to move the wastewater from low or flat areas. Research
into these types of systems revealed that it is not cost effective to sewer the uphill houses by
gravity and the downhill houses by vacuum because of the need for a sealed piping system
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 8
for vacuum service. Serving some house by conventional gravity and some by vacuum would
require two sewer collection systems in the County ROW.
The vacuum interface valve that would be located on each property requires frequent
maintenance checks to ensure proper operation. These checks should be done by trained
maintenance personnel but since these valves would be on private property, the responsibility
would fall on the homeowner to hire trained personnel or obtain training on the system.
Another drawback is that the vacuum interface valves typically fail open to minimize the
chance of spills. A failed valve will therefore result in the County-owned vacuum pumping
system to run constantly (normal operation would be intermittent to save energy). County
maintenance personnel would not be able to readily find the faulty valve since they would not
have right-of-entry onto the individual properties. Also, since there is no spill or “problem”
with the sewer at the individual property with the faulty valve, there is no incentive to correct
the problem in a timely manner. Remote telemetry can be added to the vacuum interface
valves to monitor the valves via SCADA but these would also require periodic maintenance
on private property and would add to the cost of the system for monitoring at every property.
iii. Individual Grinder Pump Stations
The original concept developed for Brewer before the company dissolved was to have
individual grinder pump stations at the low-lying properties. This type of system consists of a
small pump station at each downhill home. As the pump station fills with sewage, the high
wastewater level starts a pump that evacuates the station and discharges into the gravity
sewer system on the street. Houses on the uphill side of the street would discharge sewage by
gravity into the collection system. The advantage of individual grinder pump stations is the
ability to keep the collection system as shallow as possible.
Disadvantages of this system are the need to maintain the pumps and valves on private
property and the energy used to pump the wastewater. Another disadvantage is the potential
for spills when there are mechanical failures such as, power outages, pump breakdowns, level
switch malfunctions, and clogs within the pump. Similar to the vacuum sewer system, the
mechanically intensive nature of individual grinder pump stations requires trained
maintenance personnel to perform regular checks on the system. However, since the system
belongs to the homeowner, it is their responsibility to either hire a maintenance service or
obtain the necessary training. Unlike the vacuum system, the pump stations are not “fail safe”
and will result in sewage backup in the home or a spill on the homeowner’s property that
would prompt them to seek corrective action. A rough life-cycle cost analysis of an individual
grinder pump unit resulted in an annual cost burden of $850 per house on the homeowners.
The subsurface conditions of the area at the depths required for the sewers is yet to be
investigated. If the deep gravity sewers (see below) are not feasible due to unfavorable
conditions; such as, lava tubes, then the sewers may have to be kept as shallow as possible.
This option is feasible and will be kept in consideration in the event that subsurface
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 9
conditions require it, but is not the preferred option due to the disadvantages, especially the
cost burden on the homeowners.
iv. Deep Gravity Sewers
The majority of the collection system sewer mains can be kept within the County or State
ROW and fed by gravity if the pipes are deep below the low point of the low-lying parcels.
Sewers constructed in the County of Hawaii must adhere to the Wastewater System Design
Standards of the City and County of Honolulu, which requires review and approval for sewers
deeper than 15 feet due to higher soil loading and potential difficulty when repairs are
needed. A preliminary layout of a gravity sewer system, as shown in Figure 7, resulted in
sewer depths of about 20 to 25 feet at the deepest point on the upper portions of Ohai Road
and Nahele Street, and 15 to 18 feet at the deepest point on Lokelani Street and Kilika Street.
These depths are based on running a lateral from the lowest point on a house lot up to the
street. This was used as the basis because there are houses with sinks and outhouses at the
back of the lot that are assumed to be connected to the existing collection system. The soil
depth to rock in the area as reported by USGS and verified by past geotechnical
investigations is 40 to 60 inches; therefore, excavation for the deep gravity sewers would be
mainly in rock.
A sewer along the highway or easements would be needed to service the houses on the State
highway between Kukui Road and Ohai Road. The depth, length and direction of flow for
this sewer would depend on the location of a pump station. The depth of the sewer on Opukea
Street depends on the location of a sewage pump station (see Section 4). As a worse case, the
manhole fronting the County-owned parcel (TMK 9-5-024:011) on Opukea Street would
have an invert about 30 feet deep if a pump station is constructed on that site due to the
elevation of the house at the corner of Ohai Road and Mamalahoa Hwy (TMK 9-5-024:001),
the lowest point of the former Brewer community. Although 30 feet is rather deep, it is not
unheard of at the entrance to pump stations in Honolulu which are often 3 stories deep. At the
Kuahiwi Contractors site (TMK 9-5-008:048) the ground elevation is about the same as the
house at Ohai Road and Mamalahoa Hwy resulting in sewers that are at a more reasonable
depth of about 15 feet.
This option is feasible and will be considered further. Despite the depth of the sewers in the
County ROW, the advantage of not burdening the homeowners with the cost of maintaining
the pumping system in Section 5-A-iii, above, makes this option preferred over the individual
grinder pump option.
D. Gravity Sewer from Force Main to WWTP
The primary purpose of the sewer on the Kona side of Naalehu is to convey the wastewater from
the Brewer house lots to the WWTP. A gravity sewer on Kaalaiki Road can be used to collect the
wastewater discharged from a pump station servicing the housing area on the Hilo side of the
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 10
drainage canal at either the County parcel on Opukea Street or the Kuahiwi Contractors site. The
force main can be run entirely Mauka of the highway, cross the drainage canal, and discharge into
a manhole when it reaches Kaalaiki Road. An easement would be required from the drainage
canal to the County road. There is an existing access and utility easement located on a parcel
owned by La’i LLC (TMK 9-5-025:039) that goes from Kaalaiki Road to the canal. This would
be the recommended method of conveying the sewage to the WWTP to keep construction in the
State ROW to a minimum. The force main route is discussed further in the next section.
Two commercial properties requested connection to the new collection system. These were the
Punaluu Bake Shop (TMK 9-5-025:037) and Hana Hou Restaurant (TMK 9-5-021:005). These
properties can be connected to the collection system via the gravity sewer running down Kaalaiki
Road, across the highway, and down Naalehu Spur Road to the WWTP site. There are potentially
an additional eight properties that would be newly accessible along this sewer route depending on
the disposition of Naalehu Spur Road, which is privately owned by Kuahiwi Contractors, Inc. If
the road is dedicated to the County or an easement in favor of the County spans the entire road
width, then both sides of Naalehu Spur Road would be newly accessible. If the sewer easement is
only on one side of the road, assumed to be the Hilo side to allow connection of Hana Hou
Restaurant (TMK 9-5-021:005), then only the Hilo-side properties would be newly accessible.
The proposed Kona-side collection system is presented in Figure 8.
E. Force Main from Brewer House Lots to Gravity Sewer on Kona Side
A force main will be needed to convey the wastewater from the WWPS that serves the former
Brewer house lots to the gravity sewer going to the WWTP on the Kona side. The force main can
be kept out of the State ROW by running the pipe along easements and County roads. Figure 8
shows the possible force main routes from the County parcel and the Kuahiwi Contractors sites.
The approximate force main lengths from the County parcel and Kuahiwi Contractors parcel are
1300 LF and 2800 LF, respectively.
Both WWPS options will require crossing the concrete drainage canal that divides the Kona side
of Naalehu from the Hilo side. The force main can go either above the canal on a support
structure, or under the canal. There is an existing pedestrian bridge crossing the canal that can be
reconstructed and used to support the new force main; however, the County DEM is not in favor
of this option due to the possibility of the structure impeding flow through the canal and
ownership of the bridge structure being a burden on DEM personnel who are not set up for bridge
inspection and maintenance duties. Routing the force main under the canal can be done by either
cutting the concrete canal structure and laying the pipe in an open trench or tunneling under the
canal. Cutting the structure poses some risk should a rain storm occur while the trench is open or
repaired concrete is curing. Tunneling would be costly due to the depth and equipment needed to
micro-tunnel or the shoring required to excavate under the structure. Further discussions with a
geotechnical engineer will be needed to determine the best method to cross the canal while
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 11
limiting risk during construction. For planning purposes, it will be assumed that the canal
crossing will be approximately 100 LF using micro-tunneling as a worse case.
6 COLLECTION SYSTEM COSTS AND RECOMMENDATIONS
Planning level capital costs were developed for the collection system options developed above. The
costs are presented in Table 2. Basis for the costs are presented in Table 3. Cost basis numbers are
from recent past project construction and bid costs inflated to the current year.
Table 2: Collection System Costs
Table 3: Cost Basis
Unit Cost
Deep WWPS at County Parcel $7.1 million
Typical WWPS at Kuahiwi Contractors Parcel $4.9 million
Gravity Sewers $1100/LF
Deep Gravity Sewers in Rock $1600/LF
Deep Sewers (Tunneled) $7000/LF
Sewer Force Mains (not including tunneled section under canal) $1000/LF
Note: Cost of individual grinder pump system based on design cost estimate of $5.6 million prepared in 2012 inflated to
2020 at 6% average inflation ($5.6m x 1.06^(2020-2012) = $9 million)
The overall recommendation for the collection system is to use deep gravity sewers for the former
Brewer housing area. Two backyard easements would be used to connect four properties to the
collection system. These easements have already been surveyed and are located on the south side of
TMK 9-5-024:009 and TMK 9-5-024:010. These easements would expedite implementation by
avoiding the need for a sewer in the State ROW to serve three of the properties. Two commercial
properties requested connection to the new collection system. These were the Punaluu Bake Shop
(TMK 9-5-025:037) and Hana Hou Restaurant (TMK 9-5-021:005). These properties can be
connected to the collection system via a gravity sewer running down Kaalaiki Road, across the
highway, and down Naalehu Spur Road. There are up to an additional fifteen properties that would be
newly accessible along this sewer route. The newly accessible house lots along with the newly
accessible properties along the sewer to serve the commercial lots brings the total newly accessible
properties to 39, exceeding the number identified in the Consent Order. If the WWPS is located on
the County parcel, the overall estimated cost of the system would be $24.4 million. If the the WWPS
Deep Gravity Sewer at House Lots $12 million
Individual Grinder Pumps at House Lots $9 million
WWPS at County Parcel $7.1 million + $1.3 million FM = $8.4 million
WWPS at Kuahiwi Contractors $4.9 million + $2.8 million FM = $7.7 million
Canal Crossing (Tunneled) $0.7 million
Gravity Sewer from FM to Proposed WWTP $3.3 million
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 12
is located on the Kuahiwi Contractors site, overall estimated cost would be $23.7 million. The
recommended collection system options are presented in Figure 9 and 10.
If using deep sewers in the former Brewer house lots is not feasible due to subsurface conditions, the
estimated cost of the collection system would be $21.4 million if the WWPS is on the County parcel,
and $20.7 million if the WWPS is on the Kuahiwi Contractors site. However, there would be added
cost for the homeowners with parcels below the road of approximately $850 per year per house to
maintain the pumps. A summary of the overall costs is presented in Table 4.
Table 4: Overall Planning Level Cost Estimates
Deep Gravity Sewers Individual Pumps
County WWPS at County Parcel $24.4 million $21.4 million
County WWPS at Kuahiwi Contractors Site $23.7 million $20.7 million
7 COLLECTION SYSTEM PHASING
The collection system can be constructed in phases to expedite the closure of the LCCs. As a
minimum, the collection system would have to intercept the existing sewers entering the LCCs and
convey the sewage to a pump station. To minimize the need for temporary facilities that would be
removed when the collection system is completed in a second phase, it would be beneficial to
construct the permanent WWPS as part of Phase 1. Phase 1 would therefore consist of the following:
a. Construct Gravity Sewer on Kaalaiki Road and Naalehu Spur Road to the WWTP
b. Construct the WWPS and force main
c. Construct the gravity sewer on Opukea Street and Ohai Road to intercept existing sewers and
connect to the WWPS
The sewer system for the proposed Phase 1 is presented in Figures 11 and 12. Sub-phases “a” and
“b” can be done concurrently; however, intercepting the existing sewer system should be done at the
end of Phase 1. This is so that the if there are issues encountered when constructing the sewers, the
main WWPS and means of conveying the flow to the WWTP will be in place so that bypass pumping
to the WWPS can be used if needed. If the main WWPS and conveyance sewers to the WWTP were
not in place, the contractor would have a more difficult time with bypass pumping to the WWTP or
would have to truck sewage if a problem occurs. The new WWPS would be close enough to allow
temporary piping to be routed from the problem area into the wet well.
The cost to implement Phase 1 would be about $15.3 million with the WWPS on the County parcel,
and about $15.1 million with the WWPS on the Kuahiwi Contractors site (not including land
acquisition costs). A phased cost summary is presented in Table 5.
Memorandum
Naalehu Collection System Improvements
May 1, 2020
Page 13
Table 5: Phased Cost Summary
Deep Gravity Sewers Individual Pumps
County Parcel Kuahiwi Parcel County Parcel Kuahiwi Parcel
Phase 1 $15.3 million $15.1 million $12.3 million $12.1 million
Phase 2 $9.1 million $8.6 million $6.1 million $5.6 million
Total $24.4 million $23.7 million $18.4 million $17.7 million
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LEGEND
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Existing Sewer Mains
Existing Service Area
SC AL E AS SHOW N
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NAAL EH U WASTEWATER TREATMENT PLANT
Existing Na aleh u Wastewater System
FIGURE
1-1
Existing Large Capacity
Cesspool (LCC 4)
Existing Large Capacity
Cesspool (LCC 3)
Existing Large Capacity
Cesspool (LCC 5)
Naalehu
Cemetery
Naalehu
Elementary
School
Naalehu
Park
Naalehu
Hongwanji
Punaluu Bakery
TMK 9-5-025:037
Hana Hou
Restaurant
TMK 9-5-021:005
Iglesia ni Cristo
Church
TMK 9-5-009:079
From:
Figure 2: Naalehu TopographyElev 760± High PointElev 660± Kukui Int.Elev 690± WWTPElev 650± Niu Int.Elev 640± Niu/Poha Int.Elev 645± Ohai IntElev 640± ChurchSource: Onsite Sewage Disposal Systems ‐Hawaii [arcgis_rest_services_Infrastructure_MapServer_26
500 ft
Potential SPS Location
Chinese Society Church
TMK 9-5-008:012
Kuahiwi Contractors
TMK 9-5-008:048
Naalehu School
TMK 9-5-009:006
Naalehu Park
TMK 9-5-021:023
Thy Word Ministries
TMK 9-5-021:035
Senior Center
TMK 9-5-024:007
County Parcel
TMK 9-5-024:011
Figure 3: Possible WWPS Locations
HELCO XFRMR
AND METER
GENERATOR
BLDGODOR
CONTROL
WWPS
31 FT DEEP
PUMP
STARTERS AND
CONTROLS
VALVE VAULT
EMERGENCY
PUMP
CONNECTION SFM
Figure 4
Naalehu Wastewater Collection System
Pump Station Layout on County Parcel
Figure 5 Pump Station on Portion of Kuahiwi Contractors Parcel
Box culvert under hwy (approx 4'x4')Appears to be a swaleAnecdotal reports of flooding over hwy at culvertProposed WWPS siteFigure 6
500 ft
Legend:
Former Brewer House Lots
Newly Accessible (21)
Private Lateral in Easement
Gravity Sewer
Figure 7: Former Brewer House Lots Collection System
500 ft
Potential Gravity Sewer
Alignment To WWTP
Discharge SMH
Canal Crossing
Highway Bridge
Crossing
Figure 8
Kona Side Collection
System
Legend:
Properties Requesting Connection (2)
Newly Accessible (11)
Potentially Newly Accessible (2)
Potential WWPS at Kuahiwi
Contractors
Potential WWPS at County
Parcel
Potential SFM Route from
Kuahiwi Contractors
Potential SFM Route from
County Parcel
Alternate FM and Sewer Route
500 ft
Gravity Sewer
Alignment To WWTP
Iglesia ni Cristo
Church
TMK 9-5-009:079
Figure 9
Potential WWPS on Kuahiwi Parcel
SFM Channel Crossing at Melia St
Sewer Easement on Hilo Side of Naalehu Spur Rd
Hana Hou
Restaurant
TMK 9-5-021:005 Legend:
Former Brewer House Lot
Properties Requesting Conn (1+2)
Newly Accessible (21+11)
Potential Newly Accessible (2+2)
Pump Station Location
Gravity Sewer
Private Lateral in Easement
Easement
Sewer Force Main
Punaluu Bakery
TMK 9-5-025:037
Easement on Hilo side of
Naalehu Spur Rd
Waterline easement at back of
properties. Likely WL
easement will become a wider
utility easement for water,
sewer, and access. Properties
adjacent to easement are
potential newly accessible.
500 ft
Gravity Sewer
Alignment To WWTP
Iglesia ni Cristo
Church
TMK 9-5-009:079
Figure 10
Potential WWPS on County Parcel
SFM Channel Crossing at Melia St
Sewer Easement on Hilo Side of Naalehu Spur Rd
Hana Hou
Restaurant
TMK 9-5-021:005 Legend:
Former Brewer House Lot
Properties Requesting Conn (1+2)
Newly Accessible (21+11)
Potential Newly Accessible (0+2)
Pump Station Location
Gravity Sewer
Private Lateral in Easement
Easement
Sewer Force Main
Punaluu Bakery
TMK 9-5-025:037
Easement on Hilo side of
Naalehu Spur Rd
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Feet
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LEGEND
")Existing Large Capacity Cesspool (LCC)
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Existing Sewer Mains
Existing Service Area
SC AL E AS SHOW N
JO B NO .: 1514 94
NAAL EH U WASTEWATER TREATMENT PLANT
Existing Na aleh u Wastewater System
FIGURE
1-1
Existing Large Capacity
Cesspool (LCC 4)
Existing Large Capacity
Cesspool (LCC 3)
Existing Large Capacity
Cesspool (LCC 5)
Naalehu
Cemetery
Naalehu
Elementary
School
Naalehu
Park
Naalehu
Hongwanji
SFM
WWPS
Gravity
Sewer to
WWTP
11
From:
Proposed Phase 1
WWPS at Kuahiwi Contractors Site
Phase 1 Gravity Sewer
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M A IA S T
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Feet
±
LEGEND
")Existing Large Capacity Cesspool (LCC)
P Existing Sewer Manhole (SMH)
Existing Sewer Mains
Existing Service Area
SC AL E AS SHOW N
JO B NO .: 1514 94
NAAL EH U WASTEWATER TREATMENT PLANT
Existing Na aleh u Wastewater System
FIGURE
1-1
Existing Large Capacity
Cesspool (LCC 4)
Existing Large Capacity
Cesspool (LCC 3)
Existing Large Capacity
Cesspool (LCC 5)
Naalehu
Cemetery
Naalehu
Elementary
School
Naalehu
Park
Naalehu
Hongwanji
SFM
WWPS
Gravity
Sewer to
WWTP
12
From:
Proposed Phase 1
WWPS at County Parcel
Phase 1 Gravity Sewer
Appendix
Pump Station Cost Estimates
Pump Station Option Summary TableCounty Parcel Vertical Shaft Machine 7,700,000$ *County Parcel Dig and Shore 7,100,000$ Kuahiwi Site Minimum VSM 6,100,000$ * #Kuahiwi Site Minimum Dig and Shore 4,900,000$ #Kuahiwi Site Large, Dig and Shore 5,600,000$ #Notes: * Includes full cost of mobilizing VSM to Hawaii. If VSM is usedfor any other purposes (e.g., trenchless pipe installation, deep SMHsetc.) then mobilization cost will get distributed, # Does not include cost of stormwater control that may berequired due to flooding issues at SE corner of site
County ParcelVertical Shaft Machine (Herrenknecht VSM 8000 at 4.5 m diameter)DESCRIPTION QTY UM MATERIAL LABOR EQUIPMENTUNIT COSTTOTALMobilization 1 LS 800,000.00$ 800,000$ Clearing and grubbing10,000 sf 8.00$ 3.00$ 11.00$ 110,000$ Machine setup 1 LS 60,000.00$ 60,000$ Wet well shaft 35 ft 15,000.00$ 12,000.00$ 3,000.00$ 30,000.00$ 1,050,000$ Haul Spoils 230 cy 13.00$ 8.00$ 21.00$ 4,830$ Septage pumping (keep LCC low)2 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ 24,600$ Septage hauling2 mo 14,400.00$ 3,000.00$ 17,400.00$ 34,800$ Concrete mat foundation 20 cy 750.00$ 225.00$ 12.00$ 987.00$ 19,740$ Wet well structure; 8' dia, 9" wall 31 ft 500.00$ 100.00$ 250.00$ 850.00$ 26,350$ Wet well base 1 ea 1,750.00$ 800.00$ 300.00$ 2,850.00$ 2,850$ Wet well top slab, 12'x12'x10"thk 4 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 5,940$ Wet well hatch, ss and aluminum 1 ea 2,300.00$ 500.00$ 90.00$ 2,890.00$ 2,890$ Wet well interior coating 1000 sf 85.00$ 20.00$ 10.00$ 115.00$ 115,000$ Wet well exterior moisture prot 1045 sf 12.00$ 10.00$ 2.00$ 24.00$ 25,080$ Engineered backfill 140 cy 47.00$ 42.00$ 20.00$ 109.00$ 15,260$ Subm Pumps, 400 gpm, 80 ft TDH 2 ea 3,000.00$ 1,800.00$ 180.00$ 4,980.00$ 9,960$ Disch elbows and guides 2 ea 1,500.00$ 1,200.00$ 180.00$ 2,880.00$ 5,760$ Valve vault structure 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Emergency pump conn vault 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Gate Valve, 6" 5 ea 910.00$ 175.00$ 85.00$ 1,170.00$ 5,850$ Check valve, 6" 2 ea 1,050.00$ 175.00$ 85.00$ 1,310.00$ 2,620$ Quick connect hose coupling 1 ea 400.00$ 100.00$ 85.00$ 585.00$ 585$ 90 bend, FExFE, 6" 3 ea 1,005.00$ 150.00$ 85.00$ 1,240.00$ 3,720$ Tee, FExFE, 6" 1 ea 1,250.00$ 225.00$ 85.00$ 1,560.00$ 1,560$ 45 bend, MJ, 6" 4 ea 935.00$ 150.00$ 85.00$ 1,170.00$ 4,680$ Wye, MJ, 6" 2 ea 1,270.00$ 225.00$ 85.00$ 1,580.00$ 3,160$ Plug, MJ, 6" 1 ea 685.00$ 75.00$ 85.00$ 845.00$ 845$ DI pipe, FE, 6" 80 LF 185.00$ 25.00$ 15.00$ 225.00$ 18,000$
DI pipe, MJ, 6" 150 LF 180.00$ 25.00$ 15.00$ 220.00$ 33,000$ Sewer trench excavation, soft270 cy 25.00$ 7.00$ 32.00$ 8,640$ Sewer trench excavation, rock110 cy 175.00$ 35.00$ 210.00$ 23,100$ Haul Spoils380 cy 13.00$ 8.00$ 21.00$ 7,980$ Trench Shoring, 0‐10 ft2200 sf 2.00$ 5.00$ 3.00$ 10.00$ 22,000$ Trench Shoring 10‐20 ft2200 sf 2.50$ 7.00$ 3.00$ 12.50$ 27,500$ Trench Shoring 20‐27 ft, rock1540 sf 3.50$ 9.00$ 5.00$ 17.50$ 26,950$ Septage pumping (keep LCC low)1.5 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ 18,450$ Septage hauling1.5 mo 14,400.00$ 3,000.00$ 17,400.00$ 26,100$ Influent sewer, 14" DI, lined110 LF 260.00$ 45.00$ 25.00$ 330.00$ 36,300$ Reinf conc jkt6.3 cy 950.00$ 350.00$ 55.00$ 1,355.00$ 8,537$ CLSM Backfill285 cy 300.00$ 5.00$ 10.00$ 315.00$ 89,775$ Backfill41 cy 20.00$ 42.00$ 10.00$ 72.00$ 2,952$ Deep manhole (27 ft)1 ea 7,500.00$ 3,300.00$ 1,500.00$ 12,300.00$ 12,300$ Manhole interior coating355 sf 85.00$ 20.00$ 10.00$ 115.00$ 40,825$ SMH exterior moisture protection410 sf 12.00$ 10.00$ 2.00$ 24.00$ 9,840$ Odor control unit 1 ea 7,150.00$ 6,000.00$ 400.00$ 13,550.00$ 13,550$ Generator Bldg 320 sf 250.00$ 265.00$ 10.00$ 525.00$ 168,000$ Roofing membrane 5.8 sq 3,000.00$ 2,000.00$ 170.00$ 5,170.00$ 29,986$ Block sealant and paint 700 sf 11.00$ 10.00$ 4.00$ 25.00$ 17,500$ Acoustic insulation 700 sf 90.00$ 20.00$ 5.00$ 115.00$ 80,500$ Acoustic louvers 144 sf 245.00$ 50.00$ 60.00$ 355.00$ 51,120$ Generator w/base mounted tank 1 ea 127,000.00$ 35,000.00$ 800.00$ 162,800.00$ 162,800$ Conc inertia pad for generator 6 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 8,910$ Conc fueling pad 3.5 cy 750.00$ 225.00$ 12.00$ 987.00$ 3,455$ Pervious pavement road5000 sf 50.00$ 30.00$ 9.00$ 89.00$ 445,000$ 3' Grade adjustment wall360 LF 625.00$ 475.00$ 5.00$ 1,105.00$ 397,800$ Fence 426 LF 45.00$ 35.00$ 5.00$ 85.00$ 36,210$ Gate 1 ea 950.00$ 500.00$ 30.00$ 1,480.00$ 1,480$ 2" water service120 LF 75.00$ 9.00$ 2.00$ 86.00$ 10,320$ 2" water meter box1 ea 250.00$ 200.00$ 15.00$ 465.00$ 465$ Water meter1 LS 1,500.00$ 1,500$
General civil site work 10000 sf 20.00$ 200,000$ HELCO xfrmr and fees 1 LS 125,000.00$ 125,000$ SCADA and security system 1 LS 95,000.00$ 95,000$ Electrical, incl instrumentation 1 LS 377,310.60$ 377,311$ Adder for deeper sewers2000 lf 105.00$ 235.00$ 125.00$ 465.00$ 930,000$ SUBTOTAL 5,906,945$ CONTINGENCY (30%) 1,772,083$ TOTAL 7,679,028$
County ParcelConventional Dig and ShoreDESCRIPTION QTY UM MATERIAL LABOR EQUIPMENTUNIT COSTTOTALMobilization 1 LS‐$ ‐$ Clearing and grubbing10,000 sf 8.00$ 3.00$ 11.00$ 110,000$ Mud walls for water control 75 cy 600.00$ 200.00$ 200.00$ 1,000.00$ 75,000$ Excavation soft material 296 cy 164.71$ 85.00$ 249.71$ 73,914$ Excavation rock 80 cy 500.00$ 175.00$ 675.00$ 54,000$ Haul Spoils 376 cy 13.00$ 8.00$ 21.00$ 7,896$ Septage pumping (keep LCC low)4 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ 49,200$ Septage hauling4 mo 14,400.00$ 3,000.00$ 17,400.00$ 69,600$ Shoring, 0‐10 ft 800 sf 45.00$ 200.00$ 120.00$ 365.00$ 292,000$ Shoring 10‐20 ft 640 sf 65.00$ 320.00$ 200.00$ 585.00$ 374,400$ Shoring 20‐35 ft, rock 720 sf 160.00$ 320.00$ 225.00$ 705.00$ 507,600$ Concrete mat foundation 20 cy 750.00$ 225.00$ 12.00$ 987.00$ 19,740$ Wet well structure; 8' dia, 9" wall 31 ft 500.00$ 100.00$ 250.00$ 850.00$ 26,350$ Wet well base 1 ea 1,750.00$ 800.00$ 300.00$ 2,850.00$ 2,850$ Wet well top slab, 12'x12'x10"thk 4 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 5,940$ Wet well hatch, ss and aluminum 1 ea 2,300.00$ 500.00$ 90.00$ 2,890.00$ 2,890$ Wet well interior coating 1000 sf 85.00$ 20.00$ 10.00$ 115.00$ 115,000$ Wet well exterior moisture prot 1045 sf 12.00$ 10.00$ 2.00$ 24.00$ 25,080$ Engineered backfill 295 cy 47.00$ 42.00$ 20.00$ 109.00$ 32,155$ Subm Pumps, 400 gpm, 80 ft TDH 2 ea 3,000.00$ 1,800.00$ 180.00$ 4,980.00$ 9,960$ Disch elbows and guides 2 ea 1,500.00$ 1,200.00$ 180.00$ 2,880.00$ 5,760$ Valve vault structure 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Emergency pump conn vault 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Gate Valve, 6" 5 ea 910.00$ 175.00$ 85.00$ 1,170.00$ 5,850$ Check valve, 6" 2 ea 1,050.00$ 175.00$ 85.00$ 1,310.00$ 2,620$ Quick connect hose coupling 1 ea 400.00$ 100.00$ 85.00$ 585.00$ 585$ 90 bend, FExFE, 6" 3 ea 1,005.00$ 150.00$ 85.00$ 1,240.00$ 3,720$ Tee, FExFE, 6" 1 ea 1,250.00$ 225.00$ 85.00$ 1,560.00$ 1,560$
45 bend, MJ, 6" 4 ea 935.00$ 150.00$ 85.00$ 1,170.00$ 4,680$ Wye, MJ, 6" 2 ea 1,270.00$ 225.00$ 85.00$ 1,580.00$ 3,160$ Plug, MJ, 6" 1 ea 685.00$ 75.00$ 85.00$ 845.00$ 845$ DI pipe, FE, 6" 80 LF 185.00$ 25.00$ 15.00$ 225.00$ 18,000$ DI pipe, MJ, 6" 150 LF 180.00$ 25.00$ 15.00$ 220.00$ 33,000$ Sewer trench excavation, soft270 cy 25.00$ 7.00$ 32.00$ 8,640$ Sewer trench excavation, rock110 cy 175.00$ 35.00$ 210.00$ 23,100$ Haul Spoils380 cy 13.00$ 8.00$ 21.00$ 7,980$ Trench Shoring, 0‐10 ft2200 sf 2.00$ 5.00$ 3.00$ 10.00$ 22,000$ Trench Shoring 10‐20 ft2200 sf 2.50$ 7.00$ 3.00$ 12.50$ 27,500$ Trench Shoring 20‐27 ft, rock1540 sf 3.50$ 9.00$ 5.00$ 17.50$ 26,950$ Septage pumping (keep LCC low)1.5 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ 18,450$ Septage hauling1.5 mo 14,400.00$ 3,000.00$ 17,400.00$ 26,100$ Influent sewer, 14" DI, lined110 LF 260.00$ 45.00$ 25.00$ 330.00$ 36,300$ Reinf conc jkt6.3 cy 950.00$ 350.00$ 55.00$ 1,355.00$ 8,537$ CLSM Backfill285 cy 300.00$ 5.00$ 10.00$ 315.00$ 89,775$ Backfill41 cy 20.00$ 42.00$ 10.00$ 72.00$ 2,952$ Deep manhole (27 ft)1 ea 7,500.00$ 3,300.00$ 1,500.00$ 12,300.00$ 12,300$ Manhole interior coating355 sf 85.00$ 20.00$ 10.00$ 115.00$ 40,825$ SMH exterior moisture protection410 sf 12.00$ 10.00$ 2.00$ 24.00$ 9,840$ Odor control unit 1 ea 7,150.00$ 6,000.00$ 400.00$ 13,550.00$ 13,550$ Generator Bldg 320 sf 250.00$ 265.00$ 10.00$ 525.00$ 168,000$ Roofing membrane 5.8 sq 3,000.00$ 2,000.00$ 170.00$ 5,170.00$ 29,986$ Block sealant and paint 700 sf 11.00$ 10.00$ 4.00$ 25.00$ 17,500$ Acoustic insulation 700 sf 90.00$ 20.00$ 5.00$ 115.00$ 80,500$ Acoustic louvers 144 sf 245.00$ 50.00$ 60.00$ 355.00$ 51,120$ Generator w/base mounted tank 1 ea 127,000.00$ 35,000.00$ 800.00$ 162,800.00$ 162,800$ Conc inertia pad for generator 6 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 8,910$ Conc fueling pad 3.5 cy 750.00$ 225.00$ 12.00$ 987.00$ 3,455$ Pervious pavement road5000 sf 50.00$ 30.00$ 9.00$ 89.00$ 445,000$ 3' Grade adjustment wall360 LF 625.00$ 475.00$ 5.00$ 1,105.00$ 397,800$ Fence 426 LF 45.00$ 35.00$ 5.00$ 85.00$ 36,210$
Gate 1 ea 950.00$ 500.00$ 30.00$ 1,480.00$ 1,480$ 2" water service120 LF 75.00$ 9.00$ 2.00$ 86.00$ 10,320$ 2" water meter box1 ea 250.00$ 200.00$ 15.00$ 465.00$ 465$ Water meter1 LS 1,500.00$ 1,500$ General civil site work 10000 sf 20.00$ 200,000$ HELCO xfrmr and fees 1 LS 125,000.00$ 125,000$ SCADA and security system 1 LS 95,000.00$ 95,000$ Electrical, incl instrumentation 1 LS 379,844.85$ 379,845$ Adder for deeper sewers2000 lf 105.00$ 235.00$ 125.00$ 465.00$ 930,000$ SUBTOTAL 5,455,754$ CONTINGENCY (30%) 1,636,726$ TOTAL 7,092,480$
Kuahiwi Contractors Site, MinimumVertical Shaft Machine (Herrenknecht VSM 8000 at 4.5 m diameter)DESCRIPTION QTY UM MATERIAL LABOR EQUIPMENTUNIT COSTTOTALMobilization 1 LS $800,000.00 $800,000Clearing and grubbing8,000 sf $8.00 $3.00 $11.00 $88,000Machine setup 1 LS $60,000.00 $60,000Wet well shaft 18 ft $15,000.00 $12,000.00 $3,000.00 $30,000.00 $540,000Haul Spoils 103 cy $13.00 $8.00 $21.00 $2,163Concrete mat foundation 20 cy $750.00 $225.00 $12.00 $987.00 $19,740Wet well structure; 8' dia, 9" wall 15 ft $500.00 $100.00 $250.00 $850.00 $12,750Wet well base 1 ea $1,750.00 $800.00 $300.00 $2,850.00 $2,850Wet well top slab, 12'x12'x10"thk 4 cy $950.00 $450.00 $85.00 $1,485.00 $5,940Wet well hatch, ss and aluminum 1 ea $2,300.00 $500.00 $90.00 $2,890.00 $2,890Wet well interior coating 500 sf $85.00 $20.00 $10.00 $115.00 $57,500Wet well exterior moisture prot 440 sf $12.00 $10.00 $2.00 $24.00 $10,560Engineered backfill 64 cy $47.00 $42.00 $20.00 $109.00 $6,976Subm Pumps, 400 gpm, 80 ft TDH 2 ea $3,000.00 $1,800.00 $180.00 $4,980.00 $9,960Disch elbows and guides 2 ea $1,500.00 $1,200.00 $180.00 $2,880.00 $5,760Valve vault structure 1 ea $925.00 $250.00 $180.00 $1,355.00 $1,355Emergency pump conn vault 1 ea $925.00 $250.00 $180.00 $1,355.00 $1,355Gate Valve, 6" 5 ea $910.00 $175.00 $85.00 $1,170.00 $5,850Check valve, 6" 2 ea $1,050.00 $175.00 $85.00 $1,310.00 $2,620Quick connect hose coupling 1 ea $400.00 $100.00 $85.00 $585.00 $58590 bend, FExFE, 6" 3 ea $1,005.00 $150.00 $85.00 $1,240.00 $3,720Tee, FExFE, 6" 1 ea $1,250.00 $225.00 $85.00 $1,560.00 $1,56045 bend, MJ, 6" 4 ea $935.00 $150.00 $85.00 $1,170.00 $4,680Wye, MJ, 6" 2 ea $1,270.00 $225.00 $85.00 $1,580.00 $3,160Plug, MJ, 6" 1 ea $685.00 $75.00 $85.00 $845.00 $845DI pipe, FE, 6" 80 LF $185.00 $25.00 $15.00 $225.00 $18,000DI pipe, MJ, 6" 150 LF $180.00 $25.00 $15.00 $220.00 $33,000
Sewer trench excavation, soft700 cy 25.00$ 7.00$ 32.00$ 22,400$ Sewer trench excavation, rock0 cy 175.00$ 35.00$ 210.00$ ‐$ Haul Spoils700 cy 13.00$ 8.00$ 21.00$ 14,700$ Trench Shoring, 0‐10 ft9400 sf 2.00$ 5.00$ 3.00$ 10.00$ 94,000$ Trench Shoring 10‐20 ft1880 sf 2.50$ 7.00$ 3.00$ 12.50$ 23,500$ Trench Shoring 20‐27 ft, rock0 sf 3.50$ 9.00$ 5.00$ 17.50$ ‐$ Septage pumping (keep LCC low)0 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ ‐$ Septage hauling0 mo 14,400.00$ 3,000.00$ 17,400.00$ ‐$ Influent sewer, 14" DI, lined470 LF 260.00$ 45.00$ 25.00$ 330.00$ 155,100$ Reinf conc jkt0 cy 950.00$ 350.00$ 55.00$ 1,355.00$ ‐$ CLSM Backfill0 cy 300.00$ 5.00$ 10.00$ 315.00$ ‐$ Engineered Backfill41 cy 47.00$ 42.00$ 20.00$ 109.00$ 4,469$ Manhole (10 ft)3 ea 3,900.00$ 1,800.00$ 600.00$ 6,300.00$ 18,900$ Manhole interior coating180 sf 85.00$ 20.00$ 10.00$ 115.00$ 20,700$ SMH exterior moisture protection152 sf 12.00$ 10.00$ 2.00$ 24.00$ 3,648$ SFM trench excavation, soft0 cy 25.00$ 7.00$ 32.00$ ‐$ Haul Spoils0 cy 13.00$ 8.00$ 21.00$ ‐$ Trench Shoring, 0‐10 ft0 sf 2.00$ 5.00$ 3.00$ 10.00$ ‐$ SFM, 6" DI, coated and lined0 LF 180.00$ 25.00$ 15.00$ 220.00$ ‐$ Engineered Backfill0 cy 47.00$ 42.00$ 20.00$ 109.00$ ‐$ Odor control unit 1 ea $7,150.00 $6,000.00 $400.00 $13,550.00 $13,550Generator Bldg 520 sf $250.00 $265.00 $10.00 $525.00 $273,000Roofing membrane 8.4 sq $3,000.00 $2,000.00 $170.00 $5,170.00 $43,428Block sealant and paint 1105 sf $11.00 $10.00 $4.00 $25.00 $27,625Acoustic insulation 700 sf $90.00 $20.00 $5.00 $115.00 $80,500Acoustic louvers 144 sf $245.00 $50.00 $60.00 $355.00 $51,120Generator w/base mounted tank 1 ea $127,000.00 $35,000.00 $800.00 $162,800.00 $162,800Conc inertia pad for generator 6 cy $950.00 $450.00 $85.00 $1,485.00 $8,910Conc fueling pad 3.5 cy $750.00 $225.00 $12.00 $987.00 $3,455Pervious pavement road5000 sf 50.00$ 30.00$ 9.00$ $89.00 $445,0003' Grade adjustment wall370 LF 625.00$ 475.00$ 5.00$ $1,105.00 $408,850Fence 360 LF $45.00 $35.00 $5.00 $85.00 $30,600
Gate 1 ea $950.00 $500.00 $30.00 $1,480.00 $1,4806" water service500 LF 120.00$ 25.00$ 15.00$ 160.00$ 80,000$ 6" detector check in vault1 ea 8,000.00$ 6,000.00$ 1,000.00$ 15,000.00$ 15,000$ Fire standpipe1 ea 1,500.00$ 900.00$ 20.00$ 2,420.00$ 2,420$ 2" water service120 LF 75.00$ 9.00$ 2.00$ 86.00$ 10,320$ 2" water meter box1 ea 250.00$ 200.00$ 15.00$ 465.00$ 465$ Water meter1 LS 1,500.00$ 1,500$ General civil site work 8000 sf $20.00 $160,000HELCO xfrmr and fees 1 LS $225,000.00 $225,000SCADA and security system 1 LS $95,000.00 $95,000Electrical, incl instrumentation 1 LS $406,364.33 $406,364Additional gravel road 17,000 sf $1.75 $1.60 $0.75 $4.10 $69,700SUBTOTAL $4,675,323CONTINGENCY (30%) $1,402,597TOTAL $6,077,920
Kuahiwi Contractors Site, MinimumConventional Dig and ShoreDESCRIPTION QTY UM MATERIAL LABOR EQUIPMENTUNIT COSTTOTALMobilization 1 LS‐$ ‐$ Clearing and grubbing8,000 sf 8.00$ 3.00$ 11.00$ 88,000$ Excavation soft material 175 cy 164.71$ 85.00$ 249.71$ 43,699$ Excavation rock 0 cy 500.00$ 175.00$ 675.00$ ‐$ Haul Spoils 175 cy 13.00$ 8.00$ 21.00$ 3,675$ Shoring, 0‐10 ft 640 sf 45.00$ 200.00$ 120.00$ 365.00$ 233,600$ Shoring 10‐18 ft 384 sf 65.00$ 320.00$ 200.00$ 585.00$ 224,640$ Shoring 20‐35 ft, rock 0 sf 160.00$ 320.00$ 225.00$ 705.00$ ‐$ Concrete mat foundation 20 cy 750.00$ 225.00$ 12.00$ 987.00$ 19,740$ Wet well structure; 8' dia, 9" wall 15 ft 500.00$ 100.00$ 250.00$ 850.00$ 12,750$ Wet well base 1 ea 1,750.00$ 800.00$ 300.00$ 2,850.00$ 2,850$ Wet well top slab, 12'x12'x10"thk 4 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 5,940$ Wet well hatch, ss and aluminum 1 ea 2,300.00$ 500.00$ 90.00$ 2,890.00$ 2,890$ Wet well interior coating 480 sf 85.00$ 20.00$ 10.00$ 115.00$ 55,200$ Wet well exterior moisture prot 445 sf 12.00$ 10.00$ 2.00$ 24.00$ 10,680$ Engineered backfill 136 cy 47.00$ 42.00$ 20.00$ 109.00$ 14,824$ Subm Pumps, 400 gpm, 80 ft TDH 2 ea 3,000.00$ 1,800.00$ 180.00$ 4,980.00$ 9,960$ Disch elbows and guides 2 ea 1,500.00$ 1,200.00$ 180.00$ 2,880.00$ 5,760$ Valve vault structure 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Emergency pump conn vault 1 ea 925.00$ 250.00$ 180.00$ 1,355.00$ 1,355$ Gate Valve, 6" 5 ea 910.00$ 175.00$ 85.00$ 1,170.00$ 5,850$ Check valve, 6" 2 ea 1,050.00$ 175.00$ 85.00$ 1,310.00$ 2,620$ Quick connect hose coupling 1 ea 400.00$ 100.00$ 85.00$ 585.00$ 585$ 90 bend, FExFE, 6" 3 ea 1,005.00$ 150.00$ 85.00$ 1,240.00$ 3,720$ Tee, FExFE, 6" 1 ea 1,250.00$ 225.00$ 85.00$ 1,560.00$ 1,560$ 45 bend, MJ, 6" 4 ea 935.00$ 150.00$ 85.00$ 1,170.00$ 4,680$ Wye, MJ, 6" 2 ea 1,270.00$ 225.00$ 85.00$ 1,580.00$ 3,160$ Plug, MJ, 6" 1 ea 685.00$ 75.00$ 85.00$ 845.00$ 845$
DI pipe, FE, 6" 80 LF 185.00$ 25.00$ 15.00$ 225.00$ 18,000$ DI pipe, MJ, 6" 150 LF 180.00$ 25.00$ 15.00$ 220.00$ 33,000$ Sewer trench excavation, soft700 cy 25.00$ 7.00$ 32.00$ 22,400$ Sewer trench excavation, rock0 cy 175.00$ 35.00$ 210.00$ ‐$ Haul Spoils700 cy 13.00$ 8.00$ 21.00$ 14,700$ Trench Shoring, 0‐10 ft9400 sf 2.00$ 5.00$ 3.00$ 10.00$ 94,000$ Trench Shoring 10‐20 ft1880 sf 2.50$ 7.00$ 3.00$ 12.50$ 23,500$ Trench Shoring 20‐27 ft, rock0 sf 3.50$ 9.00$ 5.00$ 17.50$ ‐$ Septage pumping (keep LCC low)0 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ ‐$ Septage hauling0 mo 14,400.00$ 3,000.00$ 17,400.00$ ‐$ Influent sewer, 14" DI, lined470 LF 260.00$ 45.00$ 25.00$ 330.00$ 155,100$ Reinf conc jkt0 cy 950.00$ 350.00$ 55.00$ 1,355.00$ ‐$ CLSM Backfill0 cy 300.00$ 5.00$ 10.00$ 315.00$ ‐$ Engineered Backfill41 cy 47.00$ 42.00$ 20.00$ 109.00$ 4,469$ Manhole (10 ft)3 ea 3,900.00$ 1,800.00$ 600.00$ 6,300.00$ 18,900$ Manhole interior coating180 sf 85.00$ 20.00$ 10.00$ 115.00$ 20,700$ SMH exterior moisture protection152 sf 12.00$ 10.00$ 2.00$ 24.00$ 3,648$ SFM trench excavation, soft0 cy 25.00$ 7.00$ 32.00$ ‐$ Haul Spoils0 cy 13.00$ 8.00$ 21.00$ ‐$ Trench Shoring, 0‐10 ft0 sf 2.00$ 5.00$ 3.00$ 10.00$ ‐$ SFM, 6" DI, coated and lined0 LF 180.00$ 25.00$ 15.00$ 220.00$ ‐$ Engineered Backfill0 cy 47.00$ 42.00$ 20.00$ 109.00$ ‐$ Odor control unit 1 ea 7,150.00$ 6,000.00$ 400.00$ 13,550.00$ 13,550$ Generator Bldg 520 sf 250.00$ 265.00$ 10.00$ 525.00$ 273,000$ Roofing membrane 8.4 sq 3,000.00$ 2,000.00$ 170.00$ 5,170.00$ 43,428$ Block sealant and paint 1105 sf 11.00$ 10.00$ 4.00$ 25.00$ 27,625$ Acoustic insulation 700 sf 90.00$ 20.00$ 5.00$ 115.00$ 80,500$ Acoustic louvers 144 sf 245.00$ 50.00$ 60.00$ 355.00$ 51,120$ Generator w/base mounted tank 1 ea 127,000.00$ 35,000.00$ 800.00$ 162,800.00$ 162,800$ Conc inertia pad for generator 6 cy 950.00$ 450.00$ 85.00$ 1,485.00$ 8,910$ Conc fueling pad 3.5 cy 750.00$ 225.00$ 12.00$ 987.00$ 3,455$
Pervious pavement road5000 sf 50.00$ 30.00$ 9.00$ $89.00 $445,0003' Grade adjustment wall370 LF 625.00$ 475.00$ 5.00$ $1,105.00 $408,850Fence 360 LF 45.00$ 35.00$ 5.00$ 85.00$ 30,600$ Gate 1 ea 950.00$ 500.00$ 30.00$ 1,480.00$ 1,480$ 6" water service500 LF 120.00$ 25.00$ 15.00$ 160.00$ 80,000$ 6" detector check in vault1 ea 8,000.00$ 6,000.00$ 1,000.00$ 15,000.00$ 15,000$ Fire standpipe1 ea 1,500.00$ 900.00$ 20.00$ 2,420.00$ 2,420$ 2" water service120 LF 75.00$ 9.00$ 2.00$ 86.00$ 10,320$ 2" water meter box1 ea 250.00$ 200.00$ 15.00$ 465.00$ 465$ Water meter1 LS 1,500.00$ 1,500$ General civil site work 8000 sf 20.00$ 160,000$ HELCO xfrmr and fees 1 LS 225,000.00$ 225,000$ SCADA and security system 1 LS 95,000.00$ 95,000$ Electrical, incl instrumentation 1 LS 407,214.53$ 407,215$ Additional gravel road 17,000 sf 1.75$ 1.60$ 0.75$ 4.10$ 69,700$ SUBTOTAL 3,785,292$ CONTINGENCY (30%) 1,135,588$ TOTAL 4,920,880$
Kuahiwi Contractors Site, LargeConventional Dig and ShoreDESCRIPTION QTY UM MATERIAL LABOR EQUIPMENTUNIT COSTTOTALMobilization 1 LS $0.00‐$ Clearing and grubbing8,000 sf $8.00 $3.00 $11.00 88,000$ Excavation soft material 175 cy $164.71 $85.00 $249.71 43,699$ Excavation rock 0 cy $500.00 $175.00 $675.00‐$ Haul Spoils 175 cy $13.00 $8.00 $21.00 3,675$ Shoring, 0‐10 ft 640 sf $45.00 $200.00 $120.00 $365.00 233,600$ Shoring 10‐18 ft 384 sf $65.00 $320.00 $200.00 $585.00 224,640$ Shoring 20‐35 ft, rock 0 sf $160.00 $320.00 $225.00 $705.00‐$ Concrete mat foundation 20 cy $750.00 $225.00 $12.00 $987.00 19,740$ Wet well structure; 8' dia, 9" wall 15 ft $500.00 $100.00 $250.00 $850.00 12,750$ Wet well base 1 ea $1,750.00 $800.00 $300.00 $2,850.00 2,850$ Wet well top slab, 12'x12'x10"thk 4 cy $950.00 $450.00 $85.00 $1,485.00 5,940$ Wet well hatch, ss and aluminum 1 ea $2,300.00 $500.00 $90.00 $2,890.00 2,890$ Wet well interior coating 480 sf $85.00 $20.00 $10.00 $115.00 55,200$ Wet well exterior moisture prot 445 sf $12.00 $10.00 $2.00 $24.00 10,680$ Engineered backfill 136 cy $47.00 $42.00 $20.00 $109.00 14,824$ Subm Pumps, 400 gpm, 80 ft TDH 2 ea $3,000.00 $1,800.00 $180.00 $4,980.00 9,960$ Disch elbows and guides 2 ea $1,500.00 $1,200.00 $180.00 $2,880.00 5,760$ Valve vault structure 1 ea $925.00 $250.00 $180.00 $1,355.00 1,355$ Emergency pump conn vault 1 ea $925.00 $250.00 $180.00 $1,355.00 1,355$ Gate Valve, 6" 5 ea $910.00 $175.00 $85.00 $1,170.00 5,850$ Check valve, 6" 2 ea $1,050.00 $175.00 $85.00 $1,310.00 2,620$ Quick connect hose coupling 1 ea $400.00 $100.00 $85.00 $585.00 585$ 90 bend, FExFE, 6" 3 ea $1,005.00 $150.00 $85.00 $1,240.00 3,720$ Tee, FExFE, 6" 1 ea $1,250.00 $225.00 $85.00 $1,560.00 1,560$ 45 bend, MJ, 6" 4 ea $935.00 $150.00 $85.00 $1,170.00 4,680$ Wye, MJ, 6" 2 ea $1,270.00 $225.00 $85.00 $1,580.00 3,160$ Plug, MJ, 6" 1 ea $685.00 $75.00 $85.00 $845.00 845$ DI pipe, FE, 6" 80 LF $185.00 $25.00 $15.00 $225.00 18,000$
DI pipe, MJ, 6" 150 LF $180.00 $25.00 $15.00 $220.00 33,000$ Sewer trench excavation, soft700 cy 25.00$ 7.00$ 32.00$ 22,400$ Sewer trench excavation, rock0 cy 175.00$ 35.00$ 210.00$ ‐$ Haul Spoils700 cy 13.00$ 8.00$ 21.00$ 14,700$ Trench Shoring, 0‐10 ft9400 sf 2.00$ 5.00$ 3.00$ 10.00$ 94,000$ Trench Shoring 10‐20 ft1880 sf 2.50$ 7.00$ 3.00$ 12.50$ 23,500$ Trench Shoring 20‐27 ft, rock0 sf 3.50$ 9.00$ 5.00$ 17.50$ ‐$ Septage pumping (keep LCC low)0 mo 6,000.00$ 4,800.00$ 1,500.00$ 12,300.00$ ‐$ Septage hauling0 mo 14,400.00$ 3,000.00$ 17,400.00$ ‐$ Influent sewer, 14" DI, lined470 LF 260.00$ 45.00$ 25.00$ 330.00$ 155,100$ Reinf conc jkt0 cy 950.00$ 350.00$ 55.00$ 1,355.00$ ‐$ CLSM Backfill0 cy 300.00$ 5.00$ 10.00$ 315.00$ ‐$ Engineered Backfill41 cy 47.00$ 42.00$ 20.00$ 109.00$ 4,469$ Manhole (10 ft)3 ea 3,900.00$ 1,800.00$ 600.00$ 6,300.00$ 18,900$ Manhole interior coating180 sf 85.00$ 20.00$ 10.00$ 115.00$ 20,700$ SMH exterior moisture protection152 sf 12.00$ 10.00$ 2.00$ 24.00$ 3,648$ SFM trench excavation, soft0 cy 25.00$ 7.00$ 32.00$ ‐$ Haul Spoils0 cy 13.00$ 8.00$ 21.00$ ‐$ Trench Shoring, 0‐10 ft0 sf 2.00$ 5.00$ 3.00$ 10.00$ ‐$ SFM, 6" DI, coated and lined0 LF 180.00$ 25.00$ 15.00$ 220.00$ ‐$ Engineered Backfill0 cy 47.00$ 42.00$ 20.00$ 109.00$ ‐$ Odor control unit 1 ea $7,150.00 $6,000.00 $400.00 $13,550.00 13,550$ Generator Bldg 520 sf $250.00 $265.00 $10.00 $525.00 273,000$ Roofing membrane 8.4 sq $3,000.00 $2,000.00 $170.00 $5,170.00 43,428$ Block sealant and paint 1105 sf $11.00 $10.00 $4.00 $25.00 27,625$ Acoustic insulation 700 sf $90.00 $20.00 $5.00 $115.00 80,500$ Acoustic louvers 144 sf $245.00 $50.00 $60.00 $355.00 51,120$ Generator w/base mounted tank 1 ea $127,000.00 $35,000.00 $800.00 $162,800.00 162,800$ Conc inertia pad for generator 6 cy $950.00 $450.00 $85.00 $1,485.00 8,910$ Conc fueling pad 3.5 cy $750.00 $225.00 $12.00 $987.00 3,455$ Pervious pavement road7000 sf 50.00$ 30.00$ 9.00$ $89.00 $623,000
3' Grade adjustment wall484 LF 625.00$ 475.00$ 5.00$ $1,105.00 $534,820Fence 480 LF $45.00 $35.00 $5.00 $85.00 40,800$ Gate 1 ea $950.00 $500.00 $30.00 $1,480.00 1,480$ 6" water service500 LF 120.00$ 25.00$ 15.00$ 160.00$ 80,000$ 6" detector check in vault1 ea 8,000.00$ 6,000.00$ 1,000.00$ 15,000.00$ 15,000$ Fire standpipe1 ea 1,500.00$ 900.00$ 20.00$ 2,420.00$ 2,420$ 2" water service120 LF 75.00$ 9.00$ 2.00$ 86.00$ 10,320$ 2" water meter box1 ea 250.00$ 200.00$ 15.00$ 465.00$ 465$ Water meter1 LS 1,500.00$ 1,500$ General civil site work 15000 sf $20.00 300,000$ HELCO xfrmr and fees 1 LS $225,000.00 225,000$ SCADA and security system 1 LS $95,000.00 95,000$ Electrical, incl instrumentation 1 LS $475,340.03 475,340$ Additional gravel road 17,000 sf $1.75 $1.60 $0.75 $4.10 69,700$ SUBTOTAL 4,307,588$ CONTINGENCY (30%) 1,292,276$ TOTAL 5,599,864$
PART B: IWS Approach
PART B
Nāʻālehu Individual Wastewater System
Preliminary Engineering Report
Prepared for
Brown and Caldwell
&
County of Hawaiʻi, Department of Environmental Management
August 2023
THIS WORK (PART B) WAS PREPARED BY ME OR UNDER MY SUPERVISION
April 30, 2024
Yen Wen Fang Expiration Date of the License
Part B - IWS Approach
Table of Contents
1. Introduction ................................................................................................... 7
2. Different Types of IWS .................................................................................. 7
2.1 Septic System ........................................................................................ 7
2.2 Residential Aerobic Treatment Unit (ATU) ..................................................... 9
2.3 Intermittent Sand Filter (ISF) ................................................................. 11
2.4 Passive Treatment Beds ........................................................................ 13
2.5 Composting Toilet ................................................................................. 16
2.6 Incineration Toilet .................................................................................18
2.7 Greywater Reuse ..................................................................................19
3. Types of IWS Disposal Systems ....................................................................20
3.1 Absorption Bed ....................................................................................20
3.2 Leach Field ..........................................................................................21
3.3 Seepage Pits ........................................................................................22
3.4 Subsurface Drip Irrigation ..................................................................... 23
3.5 Evaporation Beds .................................................................................24
3.6 Mound Septic System ............................................................................25
4. Traditional IWS Recommendation ................................................................. 26
5. Traditional IWS Components ....................................................................... 28
5.1 Types of IWS Tanks ...............................................................................28
6. Design of IWS: DOH Chapter 11-62 Guidelines ........................................... 31
6.1 Percolation Testing ...............................................................................31
6.2 Sizing of Absorption Beds and Disposal Systems ........................................32
6.3 DOH Required Setbacks ........................................................................ 32
6.4 DOH Variance ......................................................................................33
7. Typical IWS Permitting and Construction Process ....................................... 33
7.1 Project Schedule ................................................................................. 35
8. IWS Constructability Challenges & Solutions ................................................. 38
8.1 Lack of Yard Space .............................................................................. 38
8.2 Landscaping ....................................................................................... 38
8.3 Ground Slope...................................................................................... 38
8.4 Cut Slope ........................................................................................... 39
8.5 Site Geology ....................................................................................... 39
8.6 Soil Permeability: Percolation Test Results ............................................... 41
8.7 Traffic Area ......................................................................................... 42
8.8 Existing Building Structures ................................................................... 42
8.9 Access of Large Construction Equipment .................................................. 43
8.10 Access of Maintenance Equipment ........................................................... 43
8.11 Coordination with Landowners or Tenants ................................................ 43
8.12 Absorption Beds vs. Seepage Pits ........................................................... 44
8.13 Availability of Resources and Contractors ................................................. 44
9. Technically Challenging Sites .................................................................... 45
10. Operational Considerations ....................................................................... 48
11. Economic Considerations .......................................................................... 52
References ............................................................................................................. .. 54
Appendices ............................................................................................................... 57
Appendix A - LCC Closure Properties….................................................................... A-1
Appendix B - Cost Calculations…………..................................................................... A-5
Appendix C – Topography.....................................................................................A-10
Appendix D - USGS Soil Survey…......................................................................... A-12
Appendix E - Geotech Report.…............................................................................ A-14
Appendix F - Typical IWS Layout & Components..................................................... A-23
Appendix G – Lava Tube Backfill Detail.................................................................. A-31
Appendix H – Percolation Test Results................................................................... A-33
List of Figures
Figure 1.1: Typical IWS flow diagram ...................................................................... 7
Figure 1.2: Side-view of a typical two-chambered septic tank ..................................... 8
Figure 1.3: Side-view of typical ATU ....................................................................... 10
Figure 1.4: Effluent quality of septic systems vs. ATUs in Hawaiʻi ................................ 11
Figure 1.5: Pumped discharge ISF following a septic tank .......................................... 11
Figure 1.6: Generic, open intermittent sand filter ..................................................... 12
Figure 1.7: Schematic of Presby’s Enviro-Fin Passive Treatment Bed ........................... 13
Figure 1.8: AES, Enviro-Septic, and Simple Septic .................................................... 14
Figure 1.9: Component view of a typical individual composting toilet ........................... 16
Figure 1.10: Top view of a typical urine separating toilet ........................................... 16
Figure 1.11: Top view of a central composting unit ................................................... 17
Figure 1.12: Side view of a typical incinerating toilet ................................................ 18
Figure 1.13: Typical greywater reuse system installed in parallel with septic tank .......... 19
Figure 1.14: Typical absorption filed installed following a septic tank ........................... 21
Figure 1.15: Leach field schematic ......................................................................... 21
Figure 1.16: Absorption Trenches Diagram .............................................................. 22
Figure 1.17: Typical subsurface drip irrigation installed following a septic tank .............. 24
Figure 1.18: Evapotranspiration (ET) bed ................................................................ 25
Figure 1.19: Elevated Mound System ..................................................................... 26
Figure 1.20: Common septic tank materials and shapes in Hawaiʻi .............................. 28
Figure 1.21: HAR 11-62 Table III Absorption bed sizing table ..................................... 32
Figure 1.22: Existing Large Capacity Cesspools ........................................................ 36
Figure 1.23: EPA Manual recommendation for placement of SWIS ............................... 39
Figure 1.24: Boring hole locations in Naʻalehu .......................................................... 40
Figure 1.25: Percolation test locations in Naʻalehu .................................................... 41
Figure 1.26: Problematic sites ............................................................................... 45
List of Tables
Table 1.1: Typical septic system performance in Hawaiʻi ... ......................................... 9
Table 1.2: Advantages and Disadvantages of Septic Tank Materials .............................. .29
Table 1.3: Common single family home septic tank products in Hawaiʻi. ........................ .30
Table 1.4: Septic sizing guide per DOH .................................................................... .31
Table 1.5: DOH required setbacks for wastewater systems per HAR 11-62 .................... .33
Table 1.6: Hawaiʻi Permitting and Construction Process ............................................... 35
Table 1.7: Naʻalehu LCC Replacement Schedule ......................................................... 37
Table 1.8: Percolation test results ............................................................................ 42
Table 1.9: Naʻalehu Problematic Sites ....................................................................... 46
Table 1.10: The five management models for IWS maintenance ................................. …49
Table 1.11: County and homeowner responsibilities under variations of the EPA ............ ..51
Table 1.12: Installation cost estimates ................................................................... ..52
Table 1.13: Costs associated with four IWS management models ............................... ..53
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
7
Individual Wastewater System (IWS)
1. Introduction
In Hawaiʻi, Individual Wastewater System (IWS) is defined by the Department of Health
(DOH) as a wastewater system for an individual property that receives less than 1,000
gallons per day of wastewater flow or serves five bedrooms or less. An IWS can be a
cesspool, a traditional septic system, an aerobic treatment unit (ATU), or other means of
treatment achieving National Sanitation Foundation (NSF) 40 quality effluent. Since 2016,
the State of Hawaiʻi banned the use of new cesspools due to their poor treatment quality.
Both ATUs and NSF 40 type systems are considered secondary treatment and will result in
higher operating and maintenance requirements.
2. Different Types of IWS
2.1 Septic System
A typical IWS system consists of three main components: the septic tank, distribution box,
and leach field (also known as absorption bed or drain field). The septic tank is typically
buried underground and receives wastewater from the building's plumbing fixtures (Figure
1.1). From the septic tank which has one or two compartments, effluent flows to a
distribution box, which evenly distributes the wastewater to the leach field. The leach field or
absorption bed is a network of perforated pipes or chambers laid in trenches or beds, buried
in the soil. A seepage pit, which is a vertical excavation typically lined with concrete
perforated rings, can be used in place of an absorption bed when a variance application has
been approved by the DOH. Typical IWS layout with an absorption bed, seepage pit etc. is
outlined in Appendix F.
Figure 1.1: Typical IWS flow diagram.
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
8
Figure 1.2: Side-view of a typical two-chambered septic tank (Carollo, 2021).
The underground septic tank is typically made of concrete, fiberglass, or plastic, and serves
as a primary settling chamber to remove bulk solids and floatable substances such as oil and
grease. Septic tanks usually have an inlet pipe where wastewater enters and an outlet pipe
through which partially treated effluent flows out to the distribution box. Inside the septic
tank, solid waste settles to the bottom forming sludge, while lighter materials like grease and
oils float to the top as scum. The middle layer consists of partially clarified effluent.
The size of the septic tank is determined based on the number of bedrooms in the house or
the daily wastewater flow rate. In Hawaiʻi, typical septic tank sizes for residential properties
may range from 1,000 gallons to 1,250 gallons, or more, depending on the household's
wastewater generation. Septic tanks are the most common conversion treatment technology in
Hawaiʻi.
The tank contains a mixture of wastewater and anaerobic bacteria. While the primary function of
the septic tank is to physically separate the solids and liquid into three layers: a top layer of
scum, a middle layer of liquid effluent, and a bottom layer of sludge (Figure 1.2), the
anaerobic bacteria further break down the solids that remain in the tank. The liquid effluent
flows out of the tank and into a disposal system, where it is further treated by means of soil
filtration and dispersed into the soil. The sludge and scum remain in the tank and must be
periodically pumped out by a professional septic service approximately every three to five
years, depending on usage. The drainfield can fail prematurely if periodic pumping is not
completed. If solids overflow into the drainfield, they can clog up the soil pores physically and
biologically due to excessive bio-mat growth.
The local IWS contractors are familiar with the nuances of septic system construction, which
minimizes potential installation mistakes. The other advantages of the Traditional IWS are
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
9
that it operates without the need for electricity, so operational cost is minimal and there are
no mechanical or electrical components to repair or replace.
Residential septic systems on their own remove about half of the organics in the wastewater stream
and none of the nitrogen. The overall level of treatment is thought to be much higher when well-
maintained and operating with a fully functional absorption bed (Table 1.1).
Because the level of treatment is highly dependable on the soil filtration which can vary greatly
from site to site, it is a common practice in Hawaiʻi to utilize a 3-foot soil replacement below the
drainfield to simulate a good soil filtration layer when percolation rate is expected to be faster than
one minute per inch.
Due to their simple design, septic systems are applicable for consideration to be used for the
project and will be evaluated further. Septic systems also cause less disturbance to the public
Right-of-Way (ROW) in comparison to the installation of a new wastewater collection system.
Table 1.1: Typical septic system performance in Hawaiʻi (Carollo, 2021).
1 From Table 2-1 (Water Resources Center (WRRC) University of Hawaii-Manoa, 2008).
2 From Table 4-1 in the Onsite Wastewater Treatment Survey and Assessment Study (WRRC, 2008).
3 MPN/100mL = most probably number per 100 milliliters.
2.2 Residential Aerobic Treatment Units (ATU)
An ATU is a type of wastewater treatment system that utilizes oxygen and aerobic bacteria to
break down and treat household sewage. ATUs come in many proprietary shapes and sizes
but at a minimum, systems typically include a primary settling chamber (similar to a septic
tank), an aeration chamber, where the wastewater is blended with air or oxygen while
suspended bacteria/microbes are able to grow and thrive and a clarifier chamber, where
microbes are allowed to settle out of the water (Figure 1.3). The effluent from the ATU will
discharge into the drainfield similar to the Traditional IWS.
Contaminant Typical Raw
Residential
Wastewater 1
Typical Septic Tank
Effluent Quality 2
Typical Effluent Quality
Following Soil
Absorption System 2
Total Nitrogen, mg N/L 4 14-40 39-82 ~1
TSS (mg/L) 100-400 49-161 ~4
BOD (mg/L) 100-400 132-217 <30
Fecal Coliform,
MPN/100ml 3
~106 1-106 ~13
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
10
Figure 1.3: Side-view of typical aerobic treatment unit (Carollo, 2021)
With the introduction of air and/or oxygen into the wastewater within the settling chamber, ATU
systems provide higher organic and nutrient removal rates than traditional septic systems,
making ATUs optimal for operation upstream of sensitive receiving environments. Conversely, the
added mechanical and electrical componentry leads to more frequent system downtime.
Downtime can occur when mechanical parts such as blowers, pumps, and control systems need to
be replaced, and when the ATU system requires cleaning, monitoring, and airflow adjustments. In
addition, power outages can halt the treatment process due to the mechanical components’
reliance of electricity, which can result in downtime until power is restored.
Without an effective maintenance strategy, the performance of ATUs in Hawaiʻi has been proven to
be similar to septic tanks (Figure 1.4). ATUs are less affordable than septic tanks, as they have
a higher up-front cost and a much higher O&M cost due to the requirement of contracting a
certified wastewater treatment operator by the DOH, and due to the reliance of electricity.
The continuous operation of mechanical components and exposure to moisture and organic
matter can lead to ATUs having a shorter service lifetime than septic systems, as the
components are more prone to wear and malfunction over time.
Installation of ATUs may be applicable for this project when a single dwelling has more than five
bedrooms, in accordance with the DOH Chapter 11-62 guidelines.
To Effluent
Primary
Chamber
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
11
1 ATU effluent quality, if not properly maintained without an effective maintenance strategy, can perform similar to
septic tanks in Hawai’i as stated in paragraph 2 in section 2.2.
Figure 1.4: Effluent quality of septic systems vs. ATUs in Hawaiʻi (Babcock, 2012)
2.3 Intermittent Sand Filter (ISF)
Intermittent Sand Filter (ISF)
systems provide secondary
treatment that effectively
eliminate contaminants through
the means of physical, chemical
and biological treatment
processes for primary treated
wastewater or septic tank
effluent (Figure 1.5). ISFs are
made in a variety of packed-bed
filters composed of sand or
other granular materials (EPA,
2002). Septic tanks are used as
a preliminary treatment step
before sending wastewater to an ISF. The septic tank's primary function is to separate and
settle out solids from the incoming wastewater. This helps to reduce the organic load and
solids entering the ISF, thus extending its lifespan and improving its overall performance.
Following the septic tank, the effluent is either pumped or gravity fed to the ISF.
1
Figure 1.5: Pumped discharge ISF following a
septic tank (EPA, 2023)
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
12
Wastewater is dosed onto the sand surface through a distribution network, percolating
through the sand layer to reach the underdrain system. Filtered effluent is collected for
further treatment or discharged to a leach field through a system of perforated pipes. These
systems involve an excavation or structure lined with impermeable PVC on sand bedding
filled with washed sand.
Most biochemical treatment occurs in
the top six inches, effectively
removing suspended solids and
carbonaceous biochemical oxygen
demand (BOD). Microorganisms
absorb wastewater constituents,
nearly eliminating BOD. Decreasing
carbonaceous BOD allows nitrifying
microorganisms to thrive deeper,
promoting nitrification.
Figure 1.6: Generic, open intermittent sand filter (EPA,
2002)
There are several different types of ISFs:
• Gravity Discharge ISFs: These filters use gravity to distribute wastewater onto the
sand surface usually on a sloped surface. Gravity allows for the effluent to exit the
bottom of the sand filter, where it is transferred to a drainfield through a system of
perforated pipes. The bottom of the sand filter needs to be several feet higher than the
drainfield area.
• Pumped Discharge ISFs: Pumped discharge ISFs utilize a separate pump station to
distribute treated effluent from the filter to a drainfield, allowing for more controlled and
flexible effluent distribution regardless of topography, unlike gravity discharge ISFs. The
integrity of the sand filter liner is safeguarded with discharge piping positioned above it.
• Bottomless ISFs: The bottomless ISF lacks an impermeable liner and doesn't release
wastewater to a drainfield. Instead, it directly infiltrates into the soil beneath the sand.
ISFs present a more intricate setup that includes various components like a dosing tank,
pump or siphon, distribution network, and a filter bed equipped with an underdrain system.
Regular maintenance will increase the cost due to the electricity and labor for
pumping/dosing, and overall O&M labor. There is a potential risk of the filter media in
intermittent sand filters becoming clogged, and finding local replacements for the media
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
13
could be challenging in Hawaiʻi.
For the Nāʻālehu LCC Replacement project, ISFs are not the most suitable IWS choice for
residential installation. This is due to each dwelling having limited yard space to allow area
for a septic tank, ISF, drainfield, and potentially a pump station. In addition, the sand needed
for ISFs would be difficult to source in Hawaiʻi.
Usage Case: Sand filters are a practical alternative when site conditions hinder proper
wastewater treatment and disposal through percolative beds/trenches. They are suitable for
sites with shallow soil, poor permeability, high groundwater, and limited land.
2.4 Passive Treatment Beds
Passive treatment beds are a type of secondary, decentralized wastewater treatment
technology designed to treat domestic or small-scale municipal wastewater. Passive
treatment beds need to be installed together with a septic tank and do not require the use of
electricity. This technology uses a natural process to prevent suspended solids from sealing
the underlying soil by incorporating aeration and a larger surface area for bacterial treatment
than traditional systems (Presby Environmental, Inc. 2017). Treated water is typically
discharged directly to the soil below the treatment system via a soil absorption system (New
Zealand Distributors, 2018).
Presby Environmental, Inc.
specializes in the development and
manufacturing of several passive
wastewater treatment technologies,
including Enviro-Fin (EF), Advanced
Enviro-Septic (AES), and Enviro-
Septic (ES), and Simple-Septic (SS).
The Enviro-Fin system (Figure 1.7)
consists of a centrally located Fin
Distribution Unit (FDU), a basin and a
sump made of plastic. The sump has
a waterproof area at the bottom and
small holes around it. Inside the
sump, there is a pipe that helps
equalize the wastewater between
different parts of the system. The
septic tank effluent flows into the
FDU and then gets distributed to
eight Treatment Fins that extrude Figure 1.7: Schematic of Presby's Enviro-Fin Passive
Treatment Bed (Presby Environmental)
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radially from the center and treat the wastewater. Small holes in the plastic air ducts supply
oxygen to the surfaces containing bacteria, which help break down the suspended solids in
the wastewater. The system also has green plastic fibers packed underneath the air ducts,
and specially designed fabric around the Treatment Fins and FDU, which increases the
surface area for bacterial growth and wastewater treatment.
AES (Figure 1.8) consists of a pipe made of corrugated, perforated plastic and a Bio-
Accelerator® fabric along its bottom. This fabric is surrounded by a layer of randomized
plastic fibers and sewn geo-textile fabric. Together, these materials create an ecosystem
within the pipe that efficiently treats the wastewater (Presby Environmental, Inc. 2017). The
AES technology represents the evolution of Presby's ES system, incorporating the proprietary
Bio-Accelerator® enhancement. This enhancement not only filters additional solids from the
effluent but also accelerates the treatment processes, ensures even distribution, and provides
a larger surface area for bacterial activity. Each foot of the AES pipe offers more than 40
square feet of total surface area for bacterial activity. The overall sizes of the AES system are
similar to an absorption bed and depend on the number of bedrooms in a dwelling, and the
percolation rate of the soil. Due to the higher rate of filtration, the pipes of an AES system
can be installed in closer proximity compared to the perforated pipes in an absorption bed,
which decreases the overall width of the disposal surface area needed.
The ES technology is composed in a similar fashion to the AES pipe but offers only 25 square
feet of surface area for bacterial activity for every foot of pipe. The SS pipe is comprised of a
single-layer geo-textile fabric, large diameter, gravelless pipe (LDGP) system, coupled with
Figure 1.8: AES, Enviro-Septic, and Simple-Septic 10 stages of treatment.
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Presby’s patented skimmer tabs and cooling ridges which increase bacterial growth on the
surface area of the fabric. For every foot of SS pipe, there is 15 square feet of total surface
area for bacteria to grow.
Presby has claimed that each treatment system output effluent that has been tested and
certified to NSF 40, Class I standards. The use of the Presby Passive Onsite Wastewater
Treatment & Dispersal System is permitted under Section 11-62-35(b) of the Hawaiʻi
Administrative Rules (HAR) by the Department of Health (DOH). The DOH acknowledges this
is an innovative solution that could be beneficial to the State. In addition, the DOH requires
that operational data be submitted upon request within the first twelve months after
installation when Presby products are used in place of soil absorption systems.
In general, the cost of an AES or Enviro-Fin system may be comparable to or slightly higher
than that of an ATU. Both systems require upfront investment for equipment, materials, and
installation. However, it is important to consider that the long-term costs of maintenance and
operation can differ between the two systems. ATUs typically require ongoing electrical power
for aeration and additional maintenance, such as replacing mechanical components and
monitoring systems. These factors can contribute to higher operational costs over time. On
the other hand, AES systems are designed to operate passively without the need for
electricity or mechanical components. They rely on natural processes and have fewer moving
parts, which can lead to lower long-term maintenance and operational costs. Enviro-Septic or
Simple-Septic systems have a lower system complexity than AES or Enviro-Fin Presby
technologies and are generally less expensive alternatives but require a bigger footprint.
Presby offers both in-person and online training options, covering various aspects of system
design, installation, maintenance, and regulatory requirements. Proper installation
techniques, system components, troubleshooting, and best practices for achieving optimal
performance of wastewater treatment systems are provided in the training.
While these passive treatment bed systems offer higher effluent quality without mechanical
components, they are new to the market and are not familiar to local contractors.
Furthermore, one of the key components of these systems is the requirement of “System
Sand” which is a granular material with a very specific gradation. At the time of this report,
it is not known if the local rock quarry can produce aggregates that meet that specification.
Based on the increased regulatory requirements, unfamiliarity of local contractors, and supply
chain limitations for the aggregates needed, AES, EF, SS, and ES solutions may not be
suitable treatment processes for the project.
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2.5 Composting Toilet
A composting toilet is a type of toilet that uses a combination of heat and aerobic microbial
action to break down human waste into a nutrient-rich compost. Composting toilets typically
come in three varieties:
• Individual Composting Toilets:
These waterless toilets combine
human waste with bulking material
such as sawdust, leaves, or peat
moss in a single chamber (Figure
1.9). The waste dries and composts
in-situ until the container fills and
then needs to be hauled to a
landfill that can process solid
waste in accordance with DOH
standards. Some composting
toilets also use electrical or
mechanical systems, such as an
exhaust fan, to aid in the breakdown
of waste and limit odors. These
toilets do not require water or a
connection to a sewer system,
making them an eco-friendly
alternative to traditional flush
toilets.
• Urine Diverting Toilets: Urine
diverting toilets typically have
two chambers: one for urine
and one for solid waste (Figure
1.10). The urine is typically
stored and used as a fertilizer,
while the solid waste is broken
down into compost.
• Central Composting Units: These
composters are installed outside the
home and work in conjunction with pint-flush toilets. Toilet blackwater (along
with a scoop of wood chips) flows through a 4” gravity sewer to the composter
Figure 1.10: Top view of a typical urine
separating toilet (Separett, 2023)
Figure 1.9: Component view of a typical
individual composting toilet (Sun-Mar, 2023)
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where it is introduced to a horizontal drum that collects the solids and allows
liquids to drain into the base of the enclosure (Figure 1.11). The drum must be
rotated in the forward direction once
every two days to fluff the retained solids
and rotated in the reverse direction once
every two months to drop the retained
solids into an aging drawer where the
composting process is completed. The
outputs are a drawer of composted
manure and drained liquid. A single
central composting unit can serve an
entire home and solid wastes and any
odors are kept entirely outdoors.
Composting toilets are reviewed and
approved by the DOH on a case-by-case
basis. Solids generated from composting
toilets that are land applied must meet the
requirements of HAR 11-62 Subchapter 4:
Wastewater Sludge Use and Disposal. This
treatment process may not be applicable for this project due to the regulations pertaining to
the disposal of solid waste, which could require disposal at a municipal solid waste landfill
unit in compliance with the sludge related conditions in a permit issued by the DOH. Septic
tanks require less active involvement from homeowners and do not typically require regular
emptying if properly sized and maintained. Composting toilets can also emit strong odors if
not properly maintained.
Figure 1.11: Top view of a central composting
unit (Sun-Mar, 2023)
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2.6 Incineration Toilet
An incineration toilet, also known as a thermal toilet, is a type of toilet that uses heat to turn human
waste into ash (Figure 1.12). The waste is placed into a combustion chamber where it is heated to
high temperatures, typically around 800-1000 degrees Fahrenheit, by a gas or electric burner. This
process kills any harmful bacteria and viruses and reduces the volume of waste by up to 90%. The
ash that is left can be safely disposed of in a landfill or used as a fertilizer. Incineration toilets do not
require any water, making them suitable for remote locations or areas with limited water resources.
They also produce very little smell and have no need for a septic system or connection to a sewer.
However, they do require electricity or gas to operate, and can be relatively expensive to purchase
and maintain. Further, they do not comprise a complete treatment solution. While the remaining
household gray water can be disposed of with minimal treatment, a septic tank or other treatment
unit is still required to treat kitchen blackwater, eliminating the economic advantage.
No matter the variety, composting toilets and incineration toilet technologies are significantly
lower cost than septic tanks and other IWS. Unfortunately, they do not comprise a complete
treatment solution, making them not applicable for this project.
view of a typical incinerating toilet (Cinderella, 202
Figure 1.12: Side view of a typical incinerating
toliet (Cinderella, 2023)
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2.7 Graywater Reuse
Graywater systems are systems that collect and reuse wastewater from sources such as sinks,
showers, and laundry machines. The collected water is then treated and can be used for landscape
irrigation once separated from blackwater. The wastewater streams can be separated through the
implementation of two separate wastewater piping systems in the household. Graywater can be
treated to a re-use level for distribution strictly below the soil surface or should be disposed
of to an IWS or county sewer system (CS).
In Hawaiʻi, the use of graywater systems is regulated by the State Department of Health, which
sets guidelines for the treatment and reuse of graywater. Overall, these systems are typically
expensive to install and maintain as they are installed in addition to a traditional wastewater treatment
system that’s still required to treat household blackwater. For simplicity of design, graywater systems
are less applicable for this project than a traditional septic tank system, as access to a CS is not
readily available in Nāʻālehu, which would require the reuse system to have both a septic and
graywater holding tank.
Usage Case: Used on lots with source separated plumbing that prioritizes wastewater reuse.
Figure 1.13: Typical graywater reuse system installed in parallel
with a septic tank (DOH, 2009)
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3. Types of IWS Disposal Systems
3.1 Absorption Bed
Absorption beds are the most common form of IWS disposal system installed in Hawaiʻi today.
They consist of a network of perforated pipes, each a maximum of 100 feet long and laid in trenches
1.5-3 feet below the finished grade 4-6 feet apart (Figure 1.14). Each line is laid level to allow the
gravity dispersal of treated effluent below and above each pipe, with a filter fabric covering the
top of gravel, to prevent the gravel from clogging. A minimum of 6 inches of gravel is provided
below each pipe. If the percolation rate is faster than one minute per inch, a depth of 3-foot soil
replacement shall be installed to underlie the entire absorption bed. Soil replacement shall be
washed #4 sand or cinder-soil mix with a percolation rate not faster than one minute per inch.
These systems are easy to maintain when following an effective treatment system and
microorganisms in the soil offer an added degree of treatment to the effluent as it filters through the
upper oxic layers of the soil matrix. Absorption beds, however, have a significant space requirement,
which increases with decreasing hydraulic conductivity of the soil. Additionally, absorption beds
can only be installed on a grade of less than 8%.
While conventional perforated pipe adsorption beds are not traffic rated, companies such as
Infiltrator offer a chambered dispersion product with an H-20 load rating that can also reduce the
absorption bed space requirement by 17%.
Absorption beds are applicable for this project when space permits, as they utilize natural soil
and microbial processes to treat and filter wastewater, minimizing the environmental impact.
Additionally, the relatively simple design and lower maintenance requirements make them cost-
effective and practical for residential properties.
Usage Case: Used on typical lots without spatial, groundwater level, grade, or percolation rate
constraints. Installed on flat/mild sloped terrain.
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Figure 1.15: Leach filed schematic (Nuflw Wide Bay, 2015)
Figure 1.14: Typical absorption field installed following a septic tank (Babcock, 2019)
3.2 Leach Filed
Leach fields consist of absorption trenches installed parallel to the contour line on ground
slopes up to 12%, making them suitable for steeper terrain. These trenches are non-traffic
rated, and consist of gravel, which serves as a natural filter that permits gradual seepage
into the adjacent soil. Perforated PVC pipes are commonly used to distribute wastewater into
the trenches. Additionally, filter fabric lining can be installed to prevent the gravel from
becoming clogged with soil or debris.
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Figure 1.16: Absorption Trenches Diagram (Water Resources Research
Center, & Engineering Solutions, Inc. (2008).
The DOH design requirements state absorption trenches should have a width ranging from
eighteen to thirty-six inches. Additionally, there should be a minimum vertical separation of
three feet between the bottom of the trenches and the underlying groundwater or bedrock.
Leach fields with absorption trenches are applicable for this project when the site has a grade
between 8%-12% and will be discussed further in the report.
Usage Case: Absorption trenches are typically used on steeper terrain.
3.3 Seepage Pits
Seepage pits are a vertical means of achieving the percolation area requirements for a disposal
system. These systems typically consist of a 15-30-foot-deep pit lined with stacked precast
perforated concrete rings or CMUs, to an internal diameter of 6-8 ft. Seepage pits are both less area
intensive and less expensive than absorption beds, if converted from an existing cesspool. A
seepage pit must include a cover which extends at least 12 inches beyond the seepage pit
excavation or over a provided concrete lining. An access hatch must be provided in the concrete
cover to allow inspection and maintenance of the pit. The seepage pit may be designed to be traffic
rated by providing the sufficient strength required in the design of the concrete lining and cover.
The effective area of the seepage pit is equal to the vertical wall area corresponding to the effective
depth of the pit. Slow percolation rates translate to a larger required absorption area and deeper pit
(Figure 1.21).
While seepage pits are an approved means of disposal in Hawaiʻi, they are often only permitted when
it can be demonstrated that an alternative means of disposal was not possible, i.e.,
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insufficient land area, steep terrain (>12%) or very slow percolation rates (>60 min/inch).
Where slow percolation rates present, seepage pits will need to be dug through the basalt rock
layer to reach more porous soils or a variance will be required from HAR 11-62-34 d(1)b:
Seepage pits shall not be constructed in soils having a percolation rate slower
than ten minutes per inch (weighted average) or where rapid percolation through
such soils may result in contamination of water-bearing formations or surface
water.
Seepage pits are applicable for consideration to be used for this project for site conditions
mentioned above and will be evaluated further.
Usage Case: Used on highly spatially constrained, slope constrained, or geologically constrained lots
where sufficient percolation rates can be achieved.
3.4 Subsurface Drip Irrigation
Subsurface drip irrigation is an extremely water efficient means of wastewater disposal, slowly
delivering effluent into the existing vegetation present on site within the disposal area, promoting
efficient uptake of nutrients by the microbes and plants in the soil medium (Figure 1.17). Installation
of subsurface systems often requires less disruption to the absorption area though in Hawaiʻi, they
traditionally cost more. Regular maintenance is required to ensure the continued operation of the
irrigation pump and manage biofouling in the distribution lines.
Subsurface drip irrigation may not be suitable for the project, as more O&M is required
compared to alternative wastewater disposal systems, in order to flush the drip lines to mitigate
clogging from debris. Chlorination to remove biological growth from the drip lines would also be
needed, which has a greater environmental impact than other means of disposal. Additionally,
each IWS with subsurface drip irrigation would require the incorporation of an ATU to properly
treat wastewater for reuse.
Usage Case: Used on lots that prioritize wastewater reuse, are served by an ATU, and have a robust
maintenance strategy.
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Figure 1.17: Typical subsurface drip irrigation installed following a septic tank (EPA, 2023)
3.5 Evaporation Beds
Evaporation beds, or evapotranspiration (ET) wastewater treatment systems, are utilized to remove
effluent by direct evaporation and by plant transpiration. If soil infiltration is desired,
evapotranspiration/infiltration (ETI) process can dispose of effluent by employing both evapotranspiration
and soil penetration. ET and ETI systems follow primary pretreatment units which filter out settleable and
floatable soils.
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Figure 1.18: Evapotranspiration (ET) bed (EPA, 2018)
The septic tank effluent enters the ET or ETI units through distribution pipes and reaches a porous bed. To
prevent water from seeping out, a liner is used below the bed in ET systems. Aquatic plants are grown on
the surface of the sand bed to aid in transpiration of the effluent. In ETI systems, the effluent can
percolate into the underlying soil with the absence of a liner.
Evaporation beds are sizable disposal systems that may experience overflow if the evapotranspiration rate
does not exceed the monthly precipitation by more than 2 inches a month. ET/ETIs are reviewed on a
case-by-case basis by the Department of Health.
Evaporation beds may not be appropriate for this project, as Nāʻālehu has a tropical climate with
abundant rainfall throughout the year. Additional maintenance is also required to prune and monitor plant
health to ensure the system functions effectively.
Usage Case: Arid climates where evaporation exceeds precipitation. Sensitive locations where no
subsurface disposal is desired/allowed. These disposal units are most appropriate following
ATUs but are occasionally employed after septic tanks.
3.6 Mound Septic System
When greater vertical distance from groundwater is needed, or when the soil quality or slope
is not conducive for an absorption bed or trench system, above-ground mounds of sand or
soil can be implemented to achieve desired conditions (Water Resources Research Center, &
Engineering Solutions, Inc., 2008). The process begins by preparing the land where the
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mound will be situated through tilling. Afterward, a layer of sand is spread across the tilled
area along with a distribution system. Next, the top of the mound is covered with soil from
the surrounding area and given an aesthetically pleasing landscape. A pump system is
necessary due to the influent disposal point being at a higher elevation than the treatment
system. This factor raises the overall cost of the system since electricity is required.
Figure 1.19: Elevated Mound System (EPA, 2018)
The Department of Health (DOH) evaluates the design criteria for mound disposal systems on
a case-by-case basis when systems are outside the percolation rate range of trenches and
beds. There is a three feet minimum required separation from any existing groundwater.
Mound septic systems may not be suitable for this project as the cost can be more expensive
to install and maintain compared to traditional wastewater disposal systems. This is due to
the additional design components required, such as the construction of the mound itself and
specialized fill material. Mound systems require a larger land area than other disposal
systems which can be a limitation on smaller lots.
Usage Case: In areas where limitations exist due to poor soil or proximity to groundwater.
4. Traditional IWS Recommendation
When considering an IWS alternative, existing regulations, environmental concerns, site
constraints, economics, and performance shall be taken into consideration. Overall, each
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household IWS could cost between $30,000-$150,000 to install and roughly $1,000 per year to
operate and maintain. However, associated O&M fees for household IWS are dependent on
the management model implemented, which is further discussed in Section 11.
Based on the EPA requirements for this project, the installation of traditional septic tanks with
standard absorption bed is recommended for Nāʻālehu. Per the revised AOC, IWS is a possible
alternative to be considered, however technical and environmental analysis will still need to be
conducted for Hawaiʻi County to make an informed decision. Septic tanks coupled with absorption
beds offer the lowest cost, least complex solution, with low maintenance requirements in
comparison to the other options previously discussed. Where space and grading constraints
prevent the installation of an absorption bed, an existing cesspool (if present) can be repurposed
as a seepage pit for disposal, or a new seepage pit can be installed. This alternative is being
considered for three reasons:
• Passive Operation: The traditional septic IWS offers a passive operation with minimal
O&M cost. While the ATUs offer the promise of improved performance, in practice in
Hawaiʻi, the added mechanical and electrical complexity and the operator requirement
results in higher-than-average O&M costs or facing the risk of falling into similar
treatment performance comparable to septic tanks.
• Adaptive to Small Lots: The option of disposing to seepage pits allows septic systems to
be installed particularly on spatially and geographically constrained lots.
• Familiarity: Hawaiʻi’s engineers, regulators, contractors, and septic pumpers are
familiar with septic tanks, absorption beds, and seepage pits. The ATU and CTDS, on
the other hand, are less known. Furthermore, the lack of certified wastewater operators
throughout the State will result in higher costs and reduced performance for ATU and
CTDS options.
• Cost: Traditional septic tanks don't have moving parts or require significant
mechanical components, which can reduce maintenance and repair costs over
time. Energy cost savings are also significant since septic tanks rely on natural
processes for wastewater treatment, compared to some other IWS that involve
mechanical or electrical components.
• O&M: The absence of complex components in septic tanks simplifies maintenance.
There are no pumps, blowers, or electronic controls to manage or repair, making
maintenance tasks more straightforward.
• Environmental: Septic tanks are more energy efficient than other IWS
alternatives such as ATUs, which require energy-intensive processes (aeration) for
effective treatment. Additionally, other IWS alternatives may require the use of
chemicals for treatment processes. Septic tanks generally involve fewer chemical
inputs, contributing to a lower environmental impact.
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5. Traditional IWS Components
5.1 Types of IWS Tanks
There are several septic tank providers commonly used in Hawaiʻi offering tanks of a variety of price
points and materials. Septic tanks can be made from concrete, plastic, and fiberglass (Figure 1.20),
each of which having its own set of pros and cons (Table 1.2). Where a septic tank is located beneath
a vehicular traffic area, a traffic rated concrete septic tank can be used or a structural concrete slab
designed for H-20 loading spanning a non-traffic tank may be used.
The yellow plastic tank displayed in Figure 1.20 is manufactured locally by Chemtainer in Keaau,
Hawaiʻi. This HDPE tank is the most economical type of septic tank. However, because the
material is flimsy, it is prone to be installed improperly, and has more restrictions on the location
to which it can be installed.
Septic tank manufacturers and distributers in Hawaiʻi include Jensen Precast, Ferguson
(Infiltrator Chambers), Chemtainer, and Orenco.
Figure 1.20: Common septic tank materials and shapes in Hawaiʻi (Carollo, 2021).
Rectangular, Concrete Tank Oval, Concrete Tank Cylindrical, Concrete
Tank
Rectangular, Plastic Tank Fiberglass, Oval Tank Steel, Horizontal, Cylindrical
Tank
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Table 1.2: Advantages and Disadvantages of Septic Tank Materials (Carollo, 2021).
Septic Tank Material Advantages Disadvantages
Concrete
• Durable
• Suitable for installation in traffic
area
• Less susceptible to collapse and
floatation
• May be cast-in-place for custom
shape
• Precast tanks can be more
expensive than plastic or FRP due
to shipping and installation costs
• Typically requires use of a crane for
installation
• Concrete may corrode over time
due to acidic sewer gases
Plastic (polyethylene)
• Less expensive than precast
concrete tanks (lower shipping and
installation costs)
• Manufactured locally on the island
• Plastics are typically resistant to
corrosion
• May not require a crane for
installation
• Plastic tanks may deform
depending upon quality of the
plastic and potential structural
weaknesses of the material
• If not installed properly, plastic
tanks can float if flooded
Plastic
(polypropylene)
• Less expensive than precast
concrete tanks (lower shipping and
installation costs)
• Plastics are typically resistant to
corrosion
• Locally stocked
• Higher tank rigidity. More
tolerant impact and backfill
loads
• May not require a crane for
installation
• Not a traffic rated tank without
additional structural slab
• A two half-clam shell
construction. Requires proper
factory assembly to achieve
watertightness
Fiberglass-reinforced
polyester (FRP)
• Less expensive than precast
concrete tanks (lower shipping and
installation costs)
• Variety of manufacturers and sizes
for desired footprint
• Fiberglass is typically resistant to
corrosion
• May not require a crane for
installation
• More rigid and sturdy than plastic
tanks
• Less structurally strong than
concrete tanks
• If not installed properly, fiberglass
tanks can float if flooded
Ultimately, the choice of septic tank material will depend on availability, budget, and site
constraints (Table 1.3). At a minimum, septic tanks in Hawaiʻi must comply with International
Association of Plumbing and Mechanical Officials (IAPMO) material and property standards for
septic tanks. Further, sizing and installation criteria are regulated by HAR 11-62-33. The
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1 Local list price does not include tax, contractor markup, transportation, or installation.
minimum septic tank capacity is 1,000 gallons for a household of 4 bedrooms or less and
1250 gallons minimum for households of 5 bedrooms. Septic tanks serving households
greater than 5 bedrooms will require a variance from the DOH.
Table 1.3: Common single family home septic tank products in Hawaiʻi.
Product Material Traffic
Rated
Capacity
(Gal)
Length
(in) Width (in) Height
(in)
Weight
(lbs)
Local List
Price1
Chem-
tainer
HDPE
No
1250
96
58
62
400
$3,189
Infiltrator
(via
Ferguson)
PP
No
1287
127
62.2
54.7
320
$2,863
Orenco
(via
Custom
Concrete
& Septic)
DCPD
No
1500
168
72
64.5
620
$6,850
Jensen
Precast
Concrete
Yes
1250
138
70
57
16,700
$6,850
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6. Design of IWS: DOH Chapter 11-62 Guidelines
Per the EPA Revised Administrative Order on Consent (AOC), SDWA-UIC-AOC-2017-002,
dated August 22, 2022, the County must provide wastewater services for 194 properties, and
close the Nāʻālehu Community Cesspools. The Department of Health’s Hawaiʻi Administrative
Rules, HAR 11-62-31.1, outlines general requirements for individual wastewater systems
used in lieu of wastewater treatment works. Lots to be served in the community vary in size
from 0.12 to 1.94 acres with a median size of 0.16 acres. The current Hawaiʻi Administrative
Rules for IWS installation require a minimum of 10,000 ft2 (0.23 acres) of usable land for
each system for lots constructed and documented after August 30, 1991. The Nāʻālehu
subdivision was approved for recordation in April 1966, and is exempt from this rule and
considered grandfathered in.
The maximum permitted wastewater volume entering a single wastewater system must not
surpass one thousand gallons, and this system is not allowed to cater to more than five
bedrooms, regardless of whether these bedrooms are in one dwelling unit or distributed
across two.
Table 1.4: Septic sizing guide per DOH
DOH Septic Tank Sizing Guide
No. of Bedrooms Minimum Capacity
(Gallons)
4 or less
5
1000
1250
If a single household has more than five bedrooms and requires an IWS to handle the
wastewater, then an Aerobic Treatment Units (ATUs) needs to be installed, which can handle
a larger wastewater load.
6.1 Percolation Testing
Prior to installing the IWS, a percolation test is performed to assess the soil's ability to accept
and treat the effluent. The results of this test help determine the appropriate size and design
of the system. Per HAR 11-62, soil percolation tests must be carried out at a depth of at least
three feet. If the soil composition varies between the three-foot and five-foot depths during
construction, an additional percolation test should be conducted at the level corresponding to
the bottom of the absorption system.
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6.2 Sizing of Absorption Beds and Disposal Systems
The sizing for absorption beds and disposal systems is outlined in Figure 1.21 from HAR 11-
62. Absorption beds cannot be built in soil with a percolation rate slower than sixty minutes
per inch.
Appendix A contains preliminary absorption bed sizing calculations for the properties in
Nāʻālehu using the HAR11-62 Absorption Bed Sizing Table. Percolation rates ranging from 10-
15 min/in per site were used for the basis of this calculation, which is reflective of the higher
end of the percolation test results.
Figure 1.21: HAR 11-62 Table III Absorption bed sizing table.
6.3 DOH Required Setbacks
The actual location of treatment and disposal infrastructure is limited by setback requirements.
DOH-required setbacks are presented below (Table 1.5). From a system design perspective, it is
recommended that systems should also be a minimum of 20 feet from any cut-face slopes present
on a site to avoid surfacing of treated effluent. This is a particular constriction to heavily sloped sites.
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Table 1.5: DOH required setbacks for wastewater systems: Table II, HAR 11-62.
6.4 DOH Variance
The Nāʻālehu LCC Replacement project will likely encounter the following situations where a
DOH Variance request would be needed:
• Absorption field placement due to percolation rates and property size.
• Seepage pit installation when space is limited.
• Septic tanks serving households with more than 5 bedrooms.
Variance application and review usually adds approximately two months to the permitting
process following design package review but the DOH has expressed willingness to allow the
request for variance to be included with the initial design package.
7. Typical IWS Permitting and Construction Process
The permitting and construction process for IWS begins with the Engineer of Record (EoR)
preparing and submitting a design package for DOH approval. Once DOH reviews and approves
the design package, DOH issues an “Approval for Construction” letter. While during DOH review
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process, the plumbing contractor submits the Plumbing Permit application with County DPW
Building Division for building sewer line modification. Once both permits are issued, the contractor
can start excavation of the septic tank, drainfield and pipe trenches, while the existing sewer lines
are protected in place, or a temporary bypass is installed to keep the existing system in service.
The EoR will perform a site-specific percolation test at the bottom of the drainfield excavation to
further verify the actual percolation rate and adjust drainfield sizing as necessary. Per HAR 11-62,
retesting is only required however when the soil profile at 5 feet depth is different than the soil
profile that was performed during the percolation tests. After the installation of drain rocks,
drainfield piping and the septic tank, the engineer performs a final inspection and document as-
built of the installed system before final backfilling and files a final inspection report to DOH for
review. If everything is in order, the DOH returns an “Approval for Use” letter and the building
waste line can be changed over to the newly installed IWS.
The Nā’ālehu LCC Replacement project will use a project specific approach in three principal ways:
• Properties to be Permitted in Bulk: The DOH has expressed the capacity to receive
packages in groups of 10 or more properties. This will serve to expedite the DOH review
process.
• Variance Requests: Due to preliminary data on percolation rates and property sizes, it’s
expected that DOH variances to setback constraints will be required to accommodate
the IWS installation. Where space is still overly constrained, DOH variances will be
required to allow for seepage pit installation. During the design phase, the specific lots
requiring variances will be identified, which the variance application can be submitted
prior to submitting the design application to construct, which will enable the
permitting process to go more efficiently.
• Optioned Design: The geological conditions present at a given site will not be known
until construction on that site commences. These conditions will have a significant
impact on the disposal system design. To accommodate this uncertainty in the design
and facilitate permitting, an optioned design package shall be submitted to the DOH to
allow for a field determination according to the actual percolation rates and soil
composition encountered. We would expect the in-situ soil stratum to change from
4-5 feet deep of volcanic ash soil at the surface to solid or fractured basaltic rock
below 6 feet deep. The percolation rates between the volcanic ash soil and the
basalt rock are great, so as comparing fractured and unfractured rock. Since the
absorption bed sizing greatly depends on the percolation rate, location and the
depth of required excavation, it is best to perform the percolation test at the
bottom of the excavation to represent actual conditions of design.
The timeline and deliverables for this procedure is outlined on the following page (Table 1.6).
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Table 1.6: Hawaiʻi Permitting and Construction Process1
7.1 Project Schedule
Phasing for this project should reflect deadlines as well as workforce and product availability. The
AOC requires the County to implement the selected wastewater treatment alternative for the
194 properties and to close the Nāʻālehu Community Cesspools no later than December 31,
2027. The County still needs to make a decision if the project will be bid out in groups of IWS
(multiple bid packages) or if the project will be bid out in its entirety. Two different options
for the project schedule are proposed as follows:
• Scheduling of the sites could be in accordance with the three currently open LCCs, which
are displayed in Figure 1.22 below. The smaller two LCCs, LCC 4 and 5, which serve 16
and 8 lots respectively, could be grouped together to streamline the bidding process and
timeframe. The construction of the smaller LCCs could also be treated as a pilot stage,
with lessons learned to be integrated into the design of LCC 3, which serves
approximately 138 lots. This option would streamline the amount of coordination required
to inspect each of the three groups of connected properties and is displayed in Table 1.7.
Step Timeline Party Deliverables
Design Package +
Variance Application
Preparation
4-6 months
Engineer
• Site Evaluation/Percolation
Test Result
• IWS Calculation
• Parcel map
• Plot Plan
• Simple Building Floor Plan
for number of bedroom
determination
• IWS Layout
• IWS Profile
• IWS Details
• Owner Certification form
• $100 IWS Application Fee
Design Package Review 2-4 weeks DOH Letter of Approval
Variance Application
Review 2 months DOH Letter of Approval for
Construction
Construction 1-2 weeks/property Contractor Completed IWS
Final Inspection and Final
Inspection Report (FIR)
1 day/property
1 month/report Engineer • Final Inspection Report (FIR)
• As-Builts
FIR Review 1 month DOH Approval for Use
1 Timelines are estimates, as it needs to be clarified if the design/DOH review is for the group of 10 lots or all 194 lots.
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During construction, lots should be grouped and approached with a top-down approach,
starting with lots on the north end of Nāʻālehu and working down, keeping the previous
sewer mains in mind and keeping the existing collective system active. This will enable
the households downstream to not be affected by the construction. Multiple contractors
could be awarded construction contracts for each bidding cycle which overlaps for
increased time efficiency. The County could also choose to do the procurement and
construction process separately for each of the three LCCs, starting with the smallest, LCC
5 with 8 lots as a pilot phase, and assign multiple contractors to each LCC. However, this
would increase the total time of the project due to the additional round of bidding that
would occur from ungrouping the construction of LCC 4 and 5.
• A pilot consisting of 10 sites consisting of LCC connected properties could be first
permitted and constructed prior to the remaining parcels. Lessons learned from the pilot
would be integrated into the design and permitting of the next phase of 154 LCC
connected properties. Multiple contractors would be awarded construction contracts in
10-lot bundles that may be completed simultaneously.
Figure 1.22: Existing Large Capacity Cesspools: LCC 4, LCC 3, and LCC 5 (Brown &
Caldwell, 2023).
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
Table 1.7: Nāʻālehu LCC Replacement Schedule
1 IWS construction time is an estimate. For a single contractor, it is estimated an IWS can be installed at a rate of one site per week for simple sites, and one site every two weeks where soil conditions and accessibility are less favorable. However
contractors could have multiple crews which would allow them to complete more lots per week.
2 Grouping of lots for LCC 3 can be modified to best keep the existing collection system active.
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8. IWS Constructability Challenges & Solutions
8.1 Lack of Yard Space
Lots to be served in the Nāʻālehu community vary in size from 0.12 to 1.94 acres with a
median size of 0.16 acres. Space available for IWS installation on these properties is further
limited by the presence of existing structures. As a solution, seepage pits can be installed in
lieu of absorption beds in space constrained lots, and IWS installations could be installed
encroaching into County Right-of-Way, if permitted by Hawaiʻi County.
8.2 Landscaping
Wastewater infiltration and dispersion can be affected by landform position, and thus the
selection of the IWS location needs to account for each site’s unique landscape during the
design and construction phase.
Additionally, disturbance of existing landscape can occur during the installation of an IWS,
which can be a relatively invasive process requiring large equipment like excavators, dump
trucks and cranes. Front-yard IWS installations can be utilized as an alternative to back-yard
installations if this helps to minimize the disturbance of landscape. Thorough site assessments
can help identify existing landscape features such as vegetation, trees, retaining walls, fence
walls and natural drainage patterns which can help preserve key elements in the design. Trees
may be temporarily removed and properly stored, and then later reinstalled to restore
vegetation back to the original location. Speed and care in the restoration of any displaced
and disturbed landscapes should be taken to increase homeowner satisfaction and to restore
the site to pre-construction conditions or better.
8.3 Ground slope
When analyzing the topography of the site, key features offer more design flexibility than
others. Long, planar slopes or plateaus should be prioritized when constructing an IWS over
ridges, knolls, or other mounded or steeply sloping sites. Considering the ground slope is
crucial in the design of an absorption bed to be downstream of the dwelling and septic tank.
According to the EPA Manual, subsurface flows can accumulate in the presence of swales,
depressions, or floodplains, and optimal landscape positions consist of convex slopes and flat
areas with deep, permeable soils (EPA, 2002).
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Figure 1.23: EPA Manual recommendation for placement of subsurface wastewater infiltration
system (SWIS)
Sites in Nāʻālehu have slopes that vary from 6-10% (Appendix C). This is likely to affect the
constructability of absorption beds as a method of wastewater disposal. Per HAR 11-62-34,
absorption beds shall not be installed on land with a slope gradient greater than 8%, while
absorption trenches are permitted on a slope of up to 12%. In case this slope requirement
cannot be fulfilled, the DOH would allow a seepage pit to be installed instead of an absorption
bed.
8.4 Cut Slope
Constructing an individual wastewater system (IWS) near a cut face can present challenges,
particularly in relation to potential side seepage. The excavation or cut face may pose a risk of
allowing wastewater to permeate the surrounding soil or potentially contaminate nearby
groundwater sources.
To mitigate potential side seepage into adjacent cut face slopes, the IWS should be designed
to consider the proximity to the cut face by adjusting the location and depth of the
components, such as septic tanks or absorption beds. Installing the bottom of the absorption
bed 20 feet away from the cut face slope ensures adequate distance for potential side
seepage not to occur.
8.5 Site Geology
The National Resources Conservation Service Soil Survey was consulted for site soils information
(Appendix D). The site is principally composed of Nāʻālehu medial silty clay loam and Puueo-
Nāʻālehu complex. The surface of both compositions features silty loam, but the Puueo-Nāʻālehu
complex gives way to lithic bedrock at a depth of approximately 20-40 inches.
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This data was reinforced by the boring logs from a 2007 Geotechnical Investigation Report
conducted by Masa Fujioka & Associates (Appendix E):
“The Naalehu site has been mapped by the SCS as consisting of NaC and NaD, Naalehu series soils.
NaC and NaD are Naalehu series soils, which consists of well-drained silty clay loams that formed in
volcanic ash. This soil normally overlies pahoehoe or a'a lava flows at depths of more than 40 inches.
During our site reconnaissance, we noted that the Naalehu site had been graded to form terraces with a
road and adjacent homes on each terrace. Between terraces, we noted that the between terrace slopes
consist of relatively thin near surface volcanic ash soils overlying basaltic rock.
The boring at the Septic Tank site area was drilled to a depth of 25 feet. This boring encountered topsoil
(one foot) overlying ash soil to a depth of 4.5 feet. Broken and highly vesicular basaltic rock was
encountered for the first 15 feet. The deeper rock appeared to become moderately fractured and vesicular,
with higher recovery and RQD.”
Figure 1.24: Boring hole locations in Nāʻālehu, adapted from Masa Fujioka & Associates.
Figure 1.24 displays the boring hole locations from the analysis conducted by Masa Fujioka &
Associates in Nāʻālehu. The detailed boring logs of these seven locations is located in Appendix
E.
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The underlying basalt found at the site will significantly increase the size and installation cost
of IWS. As a solution, the engineer could show in the bid document/construction drawing that
basalt rock layer is likely to be encountered, where the depth of the rock layer varies. The
Contractor should price in dealing with rock layer in the bid. Further, it will be important to
exercise caution during excavation due to the potential to encounter underground cavities and
lava tubes. Appendix G outlines the proposed solution if lava tubes are encountered.
8.6 Soil Permeability: Percolation Test Results
IWS sizing is based on the percolation rate of the receiving soil. Percolation rates were
conducted on July 31st and August 7th, 2023, at the Nāʻālehu site and ranged from 7-15
minutes/inch. The tests were conducted to a depth of 4-4.5 feet at four sites distributed
across the project (Figure 1.25). Mainly soft dirt with occasional rocks with varying sizes was
encountered during the tests with the full percolation test reports included in Appendix H.
Figure 1.25: Percolation test locations in Nā'ālehu.
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Table 1.8: Percolation test results
Measure TMK Number 2023 EPI Nā’ālehu
LCC Replacement
PER (min/in)
Test Date
Test 1 (3) 9-5-025:019 10 @ 4 ft 07/31/23 8:00am
Test 2 (3) 9-5-024:011 7 @ 4.5 ft 07/31/23 1:30pm
Test 3 (3) 9-5-024:068 8 @ 4 ft 08/07/23 12:00pm
Test 4 (3) 9-5-026:071 15 @ 4ft 08/07/23 8:00pm
8.7 Traffic Area
It is generally not good practice to install an IWS under a trafficked or otherwise concreted area. The
presence of concrete or traffic compresses the soil in distribution systems and affects the
accessibility of the system for maintenance. However, it is sometimes unavoidable on particularly
spatially constrained properties. In this event, a system may be installed underneath a driveway or
vehicle path of travel provided the system is designed to that end and traffic rated treatment
components are used. These may include products such as concrete septic tanks and/or H-20
traffic related chambered disposal beds.
Furthermore, for front-yard IWS installations, it would be necessary to incorporate traffic-
rated IWS components in potential parking areas. One alternative could be constructing
barriers (wall, bollards, etc.) to prevent vehicle traffic over the system, allowing the need for
traffic-rated IWS components to be alleviated.
8.8 Existing Building Structures
Existing structures limit available space for IWS installation. There is a possibility that some of
the existing structures are unpermitted, but the amount/extent of unpermitted structures
present is unknown. Not only can structures obstruct access points to the IWS components,
making maintenance and servicing more challenging, unpermitted building additions can
increase the wastewater flow to the IWS beyond its original design capacity. Previous
conversations with the State of Hawaiʻi Department of Health have concluded that the design
of each in Nāʻālehu should only account for the number of permitted bedrooms for each TMK
parcel. Unpermitted buildings will not contribute to the design of the IWS capacity.
Unpermitted structures will require further coordination and discussions between the County
and homeowner on addressing unpermitted structures and including existing permitted
obstructing structures that may need to be temporarily removed and reconstructed.
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8.9 Access of Large Construction Equipment
Excavators, loaders, and cranes are examples of some of the large construction equipment
needed to install an IWS. Access for this equipment is often obstructed by low roof overhang,
blockage by permanent structures, overhead utilities, vegetation, or from insufficient path
widths. Accommodating such equipment on especially small lots often requires temporarily
removing and reconstructing of fencing, walls, existing landscaping, and in some cases small
structures.
Access should be considered for installation as well as future maintenance activities. Opportunities
to resolve access issues include:
• IWS Placement: Front-yard installations are recommended for homes without sufficient path
widths to accommodate equipment access into the backyard.
• Lightweight or Cast-in-Place Technologies: The use of a crane can be avoided by specifying
cast-in-place concrete septic tanks instead of precast varieties for particularly inaccessible
locations. Alternatively, plastic and fiberglass offer lightweight alternatives for simplified
installation.
• Alternate Access Routes: Access to a property’s backyard may be accessed from an
adjoining neighbor’s property. Such access will need to obtain permission of the
neighboring homeowner.
8.10 Access of Maintenance Equipment
IWS maintenance typically includes regular inspections, septage pumping, and periodic
cleaning when a traditional septic tank is used. If systems are not inspected, septic tanks
should be pumped every 3 to 5 years depending on the size of the tank, the number of
building occupants, and household appliances and habits (EPA, 2002). In order to remove
wastewater and/or sludge from the tank, the lid must be removed, and the tank is pumped
through an access port. Debris surrounding the system must be removed, and access must be
available for the pump hose which will pump wastewater to the pump truck parked in close
proximity. Pump hoses are typically 150 feet long and can usually access the backyard of a
property from the County Right-of-Way where the pump truck is parked.
8.11 Coordination with Landowners or Tenants
The successful completion of this project necessitates that homeowners/tenants cooperate in
the design, permitting process, and during the construction phase of the project. It is
recommended for the County to continuously notify landowners or tenants of project
milestones, such as the selection of which IWS system will be installed. The County will obtain
individual Right-of-Entry (ROE) forms to access properties during the design site assessment
and topographic surveys. Separate ROE forms will be obtained for construction activities
during the construction phase. The County will need to maintain a continuous dialogue and
coordination with homeowners/tenants through the duration of the project for the project to
be successful.
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Potential challenges can occur if the homeowner has a preference on the location of the IWS. If
the IWS is not in a favorable location for the homeowner, the IWS layout can be moved to a
location with less disturbance to the homeowner to try to accommodate this request. Solutions
may include altering the system layout by adding pumps, excavating deeper, etc.
8.12 Absorption Beds vs. Seepage Pits
When setback requirements and absorption bed sizing requirements cannot be reached due to
lack of horizontal yard space, seepage pits can be employed to dispose of wastewater in a
vertical manner.
Based on a visual walk through within the ROW roadway of the site on July 20, 2023 (Section
9), a preliminary estimate of 83 seepage pits will need to be installed in lieu of absorption
beds. This estimate was made by visual inspection and would need to be confirmed by further
surveys, as backyard space was not always visual from the public roads. Sites lacking the
necessary space in the backyard for an absorption bed were assumed to require a seepage
pit, unless significant space was present in the side or front yard. Appendix A estimates the
yard area required for an absorption bed, which ranged from 330 sq. ft. to 1,330 sq. ft.,
based on the upper range of the percolation rate of the soil found (10 and 15 minutes/inch)
and the number of permitted bedrooms in each dwelling.
8.13 Availability of Resources and Contractors
As an island state, Hawaiʻi faces unique challenges when it comes to the availability of IWS.
The entire IWS market in Hawaiʻi grew from 1192 units per year in 2018 to 1414 units per
year in 2021. Based on permits issued, sourcing the 194 treatment units required for this
project will require an increase in statewide treatment unit supply and workforce size by 14%
(DOH, 2022). This will require advanced planning to overcome this logistic hurdle.
Locally based septic manufacturers include Jensen Precast on Oʻahu and Chemtainer on Hawaiʻi
Island. At present, Jensen produces approximately 40 concrete septic tanks per year. With that said,
the company has stated that they have the capacity to build one septic tank per day to keep up with
the needs of the project. The bottleneck to their current production rate has been cited as a
shortage of inspectors, contractors, and engineers in the local market. Chemtainer manufactures
polyethylene septic systems on Hawaiʻi Island but was unwilling to share their annual production
rates. Mainland treatment system manufacturers like Orenco and Infiltrator have significantly higher
production rates but will also face increased shipping costs in transporting the units to Hawaiʻi.
Material availability and delivery will be the critical path item during construction, and the design
of the IWS needs to ensure the possibility of different manufacturers being utilized is
accommodated.
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9. Technically Challenging Sites
A visual walk-through within the ROW was conducted at Nāʻālehu by EPI on July 20th, 2023.
The aim of this site visit was to identify common conditions that are present in the community
that would render an IWS installation technically difficult, due to the challenges of IWS
construction. Five properties were initially flagged during the walk-through to have such
challenging conditions, however the total number of properties with potential technical
challenges is not limited to following households identified. Each dwelling may or may not
have its own unique challenges and this section serves as an example of which challenges
may be encountered during IWS design and construction.
Figure 1.26: Examples of sites with technically challenging conditions are marked in
yellow (but are not limited to these five properties).
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Table 1.9: Examples of Nā’ālehu Problematic Sites
Site Problem Description Photo
1
Site 1 has physical barriers such as concrete
retaining walls and stairs that limit available space
for IWS installation and will be costly to remove and
reinstall. The IWS components will likely need to be
installed under the driveway, which is at a higher
elevation than the house, which may require a pump
to be included in the system design. The IWS will
also need to be traffic-rated. The IWS components
could also be installed 3-4 feet deeper than usual
under the driveway to ensure proper wastewater
drainage from the household, and to negate the
need for a pump.
The driveway will not allow sufficient space for an
absorption bed, and thus a seepage pit will need to
be installed in addition to the septic tank. Installing a
seepage pit in lieu of an absorption bed will require a
variance application to the DOH. The seepage pit will
also not meet the defined setback requirements to
the property line and existing structures and will thus
require an additional variance application.
ʻ
Address: 95-1204 Kukui Rd, Nāʻālehu, HI 96772
2
Site 2 has limited available accessible space for IWS
installation. Communication with the homeowner will
need to be made to see which household items can
be relocated or removed to ensure space for the IWS
components.
The front and side yards do not allow sufficient
space for an absorption bed, and thus a seepage pit
will need to be installed in addition to the septic
tank. Installing a seepage pit in lieu of an absorption
bed will require a variance application to the DOH.
The seepage pit will also not meet the defined
setback requirements to the property line and
existing structures and will thus require an additional
variance application.
Address: 95-5586 Nahele St, Nāʻālehu, HI 96772
3
Site 3 is situated on a slope, which may be difficult
to maneuver with installation equipment. During
installation, a temporary ramp may need to be
constructed with material such as gravel for the
equipment to be able to reach the lower level of the
yard. Physical barriers such as the estimated 6-7 feet
high retaining wall may need to be removed to
access the available yard space. In addition, this site
contains a basement that is estimated to 6 feet
below the street grade, which will require deeper
installation of IWS components or a pump.
Address: 95-5581 Nahele St, Nāʻālehu, HI 96772
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The available yard space and driveway does not
allow sufficient room for an absorption bed, and thus
a seepage pit will need to be installed in addition to
the septic tank. Installing a seepage pit in lieu of an
absorption bed will require a variance application to
the DOH. The seepage pit will also not meet the
defined setback requirements to the property line
and existing structures and will thus require an
additional variance application.
4
Site 4 has limited yard space for installation in the
front and sides, and the front yard is difficult to
access due to physical barriers and the sloped nature
of the site. The driveway/parking area is located up
higher than the house and the backyard drops in
elevation, which would require the septic system be
installed deep into the ground, if the backyard is not
accessible by neighboring sites.
The property does not have sufficient space for an
absorption bed, and thus a seepage pit will need to
be installed in addition to the septic tank. Installing a
seepage pit in lieu of an absorption bed will require a
variance application to the DOH. The seepage pit will
also not meet the defined setback requirements to the
property line and existing structures and will thus
require an additional variance application.
Address: 95-5573 Nahele St, Nāʻālehu, HI 96772
5
Site 5 has limited yard space, is situated on a slope,
and contains physical barriers that will need to be
removed. The basement level is lower than the street,
which may require a pump to be installed in the IWS
system if a front-yard installation is chosen, or a
deeper installation. This site also appears to be
abandoned.
The driveway and front yard do not have sufficient
space for an absorption bed, and thus a seepage pit
will need to be installed in addition to the septic tank.
Installing a seepage pit in lieu of an absorption bed
will require a variance application to the DOH. The
seepage pit will also not meet the defined setback
requirements to the property line and existing
structures and will thus require an additional variance
application.
Address: 95-5557 Nahele St, Nāʻālehu, HI 96772
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10. Operational Considerations
An effective Individual Wastewater System (IWS) management strategy is crucial to ensuring
distributed treatment systems are maintained and operated in a way that ensures they are
functioning properly and effectively treating wastewater. This strategy may include but is not limited
to:
• Monitoring: Regular inspections of system components, such as septic tanks and drain
fields, ensure they are functioning properly and identify and address any issues that may
arise.
• Maintenance: Proper maintenance of the system is also crucial, including regular
pumping of septic tanks, cleaning and maintenance of the distribution systems, and
proper maintenance of the treatment components. Regular maintenance can help
prevent issues such as clogs and backups, which can lead to costly repairs and potential
health hazards.
• Regulatory Compliance: Necessary permits and licenses are obtained for the system,
and required inspection and reporting schedules are met with the local regulator.
• Community Education: Information and training on proper usage and maintenance of
the systems are provided to homeowners, and any concerns or questions that may arise
are addressed.
In Hawaiʻi, centralized wastewater treatment plants and cluster systems are regulated and inspected
by the Department of Health (DOH) Wastewater Branch (Hawaiʻi Administrative Rules 11-62).
State-licensed WWTP operators are required for oversight of Wastewater Treatment plants to
ensure that systems are inspected, operated, and maintained as required. A similar regulatory
requirement does not exist for IWS in Hawaiʻi. The State DOH Wastewater Branch is responsible for
regulating IWS while operation and maintenance are currently the responsibility of the individual
homeowner. If IWS were selected to serve Nā’ālehu Community, maintenance responsibilities could
be distributed in a number of ways. Per Voluntary National Guidelines for Management of Onsite and
Clustered (Decentralized) Wastewater Treatment System, the EPA outlined five management
models that can be used for the operation and maintenance of IWS (Table 1.10).
When selecting an appropriate management model for a network of IWS it is important to take into
account the regulatory and cultural framework within which the IWS is situated. As it stands in
Hawaiʻi, IWS are currently managed similar to a combination of management Models 1 and 2 (DOH,
2016):
• Model 1: Homeowner Awareness. The DOH allows septic systems to be managed by the
homeowner under this model. Homeowners own and operate their own IWS and are
responsible for keeping the system in good working order.
• Model 2: Maintenance Contracts. The DOH requires that Aerobic Treatment Units
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(ATUs) are managed by a state licensed wastewater operator using this model.
Homeowners are required to have an active service contract with a certified operator
or factory certified representative, and a copy of that active service contract must be
submitted annually to the DOH (DOH, 2016). Elevated regulation around the
operation of ATUs is a reflection of their increased mechanical complexity and
associated maintenance demands.
Table 1.10: The five management models for IWS maintenance (EPA, 2003)
The Five Management Models
Model 1 Model 2 Model 3 Model 4 Model 5
Responsible
Management
Entity (R:ME)
Homeowner Maintenance Operation and
Awareness: Contracts: Operating Permits: Maintenance: RME Ownership:
specifies appropriate
specifies program
specifies program
specifies program
specifies that
program elements elements and elements and elements and program elements
and activities where activities where more activities where activities where and activities for
treatment systems are complex designs sustained frequent and highly treatment systems
owned and operated are employed to performance of reliable operation are owned, operated,
by individual property enhance the capacity treatment systems and maintenance of and maintained by the
owners in areas of of conventional is critical to protect decentralized systems RME, which removes
low environmental systems to accept public health and is required to ensure the property owner
sensitivity. This and treat wastewater. water quality. Limited- water resource from responsibility
program is adequate Because of treatment term operating protection in sensitive for the system. This
where treatment complexity, contracts permits are issued environments. program is analogous
technologies with qualified to the owner and Under this model, to central sewerage
are limited to technicians are are renewable for the operating permit and provides the
conventional systems needed to ensure another term if the is issued to an greatest assurance of
that require little proper and timely owner demonstrates RME instead of the system performance
owner attention. maintenance. that the system property owner to in the most sensitive
To help ensure that is in compliance provide the needed of environments.
timely maintenance with the terms and assurance that
is performed, the conditions of the the appropriate
regulatory authority permit. Performance- maintenance is
mails maintenance -based designs may performed.
reminders to owners be incorporated
at appropriate into programs with
intervals. management controls
at this level.
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
50
The AOC stipulates that the County of Hawaiʻi must administer a more active management strategy
than is typical in Hawaiʻi, either a Model 2 (Maintenance Contract) or Model 3 (Operating Permit)
management strategy for a network of IWS at Nāʻālehu. These models reflect varying degrees of
responsibility to the County and homeowner (Table 1.11). Four potential variations of these models are
outlined here for implementation on this project:
• Management Model 2A: Maintenance Contract with County In-House Staff
The County employs and trains an in-house IWS management team; purchases and
maintains its own pumping/hauling equipment; and administers the management
program. The homeowner pays a monthly sewer fee that covers a portion of the costs.
• Management Model 2B: Maintenance Contract with Third-Party Service
The County administers the management program, keeps an operations and
maintenance (O&M) schedule, and contracts out O&M activities to a third-party service
provider. The homeowner pays a monthly sewer fee that covers a portion of the costs.
• Management Model 3A: Operating Permits with O&M by Users
The County issues an operating permit to the homeowner; keeps an O&M schedule;
and sends out maintenance reminders to homeowners. The homeowner is responsible
for contracting a third-party service provider to conduct maintenance.
• Management Model 3B: Operating Permits with O&M Voucher by County
The County issues an operating permit to the homeowner; keeps an O&M schedule;
and sends out maintenance reminders with service vouchers to homeowners. The
homeowner pays a sewer fee and is responsible for contracting a third-party service
provider to conduct annual maintenance using the voucher.
These management strategies presented here are required by the AOC but are
also unique to Hawaiʻi and will present a number of barriers for implementation at
the legislative, regulatory, and public levels. The Nāʻālehu Community and
Hawaiʻi’s stakeholders at large are accustomed to Management Model 1, which is
the standard practice across the State of Hawaiʻi.
Table 1.11: County and homeowner responsibilities under variations of the EPA Management Models 2 and 3
Management
Model
2A
Brief
Description of
Management
Model
Maintenance
Contract w/
County in-
house staff
County’s Responsibility
Homeowner / User’s
Responsibility
Pros
Cons
• Funds design and construction of IWS
• Purchase equipment & train IWS
operator
• O&M of IWS including trouble calls
• Keeping record of O&M log
• Send out notices and reminders to
homeowners
• Submit IWS inspection reports and
variance renewals to State DOH
• Report IWS problem to
County
• Cooperates and allows
County staff to enter private
property and provide
maintenance of IWS
• Maintain clearance to IWS for
easy access
1. Best control on O&M
schedule
2. Ensure best IWS
performance
1. Highest cost
2. May not receive cooperation
from some homeowners/users
3. Homeowner may have more
trouble calls
4. Potential dispute between
homeowner & County on
plumbing repair cost & IWS
repair cost
2B
Maintenance
Contract w/
3rd Party
Service
• Funds design and construction of IWS
• Select/prequalify certain 3rd party
service provider (Pumper)
• Issue PO to Pumper & plumber for
annual inspection and trouble calls
• Keeping record of O&M log
• Send out notices and reminders to
homeowners
• Submit IWS inspection reports and
variance renewals to State DOH
• Report IWS problem to
County
• Cooperates and allows
service providers to enter
private property and provide
maintenance of IWS
• Maintain clearance to IWS for
easy access
1. Better control on O&M
schedule
2. Ensure better IWS
performance
3. Less County staff to
train
4. No pumping/hauling
equipment to purchase
& maintain
1. Higher cost
2. May not receive cooperation
from some homeowners/users
3. Homeowner may have more
trouble calls
4. Potential dispute between
homeowner & County on
plumbing repair cost & IWS
repair cost
3A
Operating
Permits w/
O&M by Users
• Funds design and construction of IWS
• Keeping record of O&M log
• Send out notices and reminders to
homeowners
• Enforce rules and regulations
• Issues permit to homeowner to use,
operate & maintain the IWS
• Contracts with preferred
pumper / plumber to maintain
the IWS
• Pay for the O&M service
• Submit O&M record to
County
• Submit IWS inspection
reports and variance renewals
to State DOH
1. Least cost to County
2. No O&M staff or
equipment
3. No trouble calls
1. Least control for IWS
compliance & performance
2. Conflict with non-compliant
homeowners
3. Highest cost to homeowner
3B
Operating
Permits w/
O&M Voucher
by County
• Funds design and construction of IWS
• Keeping record of O&M log
• Send out notices and reminders to
homeowners
• Enforce rules and regulations
• Pre-select qualifying service providers
• Issue vouchers to homeowners for
annual inspections and pumping
• Issues permit to homeowner to use,
operate & maintain the IWS
• Contracts with preferred pre-
qualified pumper / plumber to
maintain the IWS
• Pay for the annual O&M
service with voucher
• Submit O&M record to
County by pumper
• Submit IWS inspection
reports and variance renewals
to State DOH
1. Reasonable control on
O&M
2. Reasonable IWS
performance
3. Less County staff to
train
4. No pumping/hauling
equipment to purchase
& maintain
5. Trouble calls to be paid
for by homeowner
1. High cost to County
2. Less control of all IWS
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
52
11. Economic Considerations
When assessing the overall cost of a given system, it is important to consider the net present value
lifecycle cost taking system lifetime and installation, maintenance, and operation costs into account.
These costs can be affected by a variety of factors, including:
• Type of treatment and disposal system: The selection of different types of treatment
systems such as traffic rated tanks or aerobic treatment significantly affects overall
installed cost. For disposal, seepage pits are significantly lower cost than absorption
fields when it is possible to convert an existing cesspool. Site specific conditions will
control which options are required. For residential IWS installations subject to State
procurement regulations, capital costs per household are typically in the range of
$30,000-$100,000 (Table 1.12). Due to the potential need for repair and
reconstruction of property site elements (fencing, walls, structures, etc.) that
may need to be removed during IWS installation, the cost per household in
Nā’ālehu can be up to $150,000. At this stage of the project, it is fully unknown
the extent of reconstruction of existing site elements, and this would need to be
further determined during the design phase of the project, which can impact the
stated estimated cost.
Table 1.12: Installation cost estimates for a standard septic tank installed in conjunction with
an absorption bed (left) and seepage pit (right). Figures are based on a 3-bedroom house
and a percolation rate no slower than 5 min/inch.
Standard Absorption Bed Seepage Pit
Low (non-traffic) High (Traffic Rated) Low (non-traffic) High (Traffic Rated)
Septic Tank 3,000.00 7,000.00 3,000.00 7,000.00
D-Box 750.00 2000 .00 – –
Sewer pipe 250.00 250.00 250.00 250.00
Leach field-pipe/
chamber 500.00 3,000.00 – –
Leach field-gravel 1,000.00 500.00 – –
Cone. Ring – – 3,000.00 3,000.00
Cone. Cover – – 2,500.00 4,000.00
Soil replacement 1,500.00 1,500.00 – –
Inspection ports 500.00 500.00 – –
Misc. material 2,000.00 2,000.00 2,000.00 2,000.00
Material Total $ 9,500.00 $ 16,750.00 $ 10,750.00 $ 16,250.00
Labor / Equipment 7,500.00 15,000.00 7,500.00 15,000.00
Remoteness 5,000.00 5,000.00 5,000.00 5,000.00
Trucking for spoils 3,000.00 3,000.00 3,000.00 3,000.00
Tight working space 3,000.00 10,000.00 3,000.00 10,000.00
Relocate/reinstall/
repair 5,000.00 100,000.00 5,000.00 100,000.00
TOTAL $ 33,000.00 $ 149,750.00 $ 34,250.00 $ 149,250.00
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
53
• Operations and Maintenance cost: Operations and maintenance cost also play a big
role in the overall cost of IWS. Annual maintenance costs to the County and
homeowner vary depending on the management strategy. It is estimated that bringing
maintenance in-house is the most affordable option (Table 1.13). Annual costs over a
20-year service lifetime are further expounded in Appendix B.
Table 1.13: The costs associated with four IWS management models, assuming septic
systems with leach fields (Appendix B).
Management Model
Average Annual Cost to
County
Average Annual Cost to
Homeowner
Net
Annual
Cost to
County
Total
Annual
Dollars
Spent Third-Party Service Provider
In-House Third-Party Service Provider
County Sewer Bill1
2A: Maintenance
Contract w/ County in-
house staff
–
($956)
-
$600
($356)
($956)
2B: Maintenance
Contract w/ 3rd Party
Service
($783)
($572)
-
$600
($755)
($1,355)
3A: Operating Permits w/
O&M by Users – ($572) ($733) - ($572) ($1,305)
3B: Operating Permits w/
O&M Voucher by County ($533) ($572) - $600 ($505) ($1,105)
1 The annual average County sewer bill is based on an average of $50/month sewer bill for households in Hawai’i.
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
54
References Babcock, R., Barnes, M., Fung, A., Goodell, W., & Oleson, K. (2019). Investigation of Cesspool
Upgrade Alternatives in Upcountry Maui Final Report. University of Hawaii Manoa.
Babcock, R., Lamichhane, K. M., Cummings, M. J., & Cheong, G. H. (2014). Condition assessment
survey of onsite sewage disposal systems (OSDSs) in Hawaii. Water Science and
Technology, 70(6), 1083–1089. https://doi.org/10.2166/wst.2014.336
Carollo Engineers (2021). Cesspool Conversion Technologies Research Summary Report. Hawaii
State Department of Health.
Hawaii County Code, Chapter 21 Sewers (2016). https://www.hawaiicounty.gov/home/
showpublisheddocument/46/637032750278570000
Hawaii State Department of Business, Economic Development and Tourism. (2021). The State of
Hawaii Data Book: A Statistical Abstract. State of Hawaii Department of Business, Economic
Development, and Tourism. https://files.hawaii.gov/dbedt/economic/databook/db2021/
DB2021_final.pdf
Environmental Protection Agency. (1996, June). Wastewater Treatment: Alternatives to Septic
Systems. Environmental Protection Agency.
https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20013JJ8.txt
Environmental Protection Agency. (2002). USEPA Onsite Wastewater Treatment Systems Manual.
In United States Environmental Protection Agency (pp. 1–367).
https://www.epa.gov/sites/default/files/2015-
06/documents/2004_07_07_septics_septic_2002_osdm_all.pdf
Environmental Protection Agency (2003). Voluntary National Guidelines for Management of Onsite
and Clustered (Decentralized) Wastewater Treatment Systems . Environmental Protection
Agency. https://www.epa.gov/sites/default/files/2015-06/documents/septic_guidelines.pdf
Environmental Protection Agency. (2018) Types of Septic Systems [Overviews and Factsheets].
https://www.epa.gov/septic/types-septic-systems
Environmental Protection Agency (2010). Code of Federal Regulations, 40 C.F.R §144.80 Title 40—
Protection of Environment. https://www.govinfo.gov/content/pkg/CFR-2014-title40-vol23/
xml/CFR-2014-title40-vol23-part144.xml
Evergreen. (2023). Separett Villa urine separating toilet. Evergreen. https://evergreen.eco/en-us/
products/urine-separating-toilet-villa-9020-12v-230v
Hawaii State Department of Health. (2009). Guidelines for the Reuse of Gray Water. Hawaii
Department of Health Wastewater Branch. https://health.hawaii.gov/wastewater/
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files/2016/03/14_Gray_Water_GL.pdf
Hawaii State Department of Health. (2016) HAR 11-62 Wastewater Systems. https://health.hawaii.
gov/opppd/files/2015/06/11-62-Wastewater-Systems.pdf
Hawaii State Department of Health. (2017). Relating to Cesspools and Prioritization for Replacement.
https://health.hawaii.gov/opppd/files/2017/12/Act-125-HB1244-HD1-SD3-CD1-29th-
Legislature-Cesspool-Report.pdf
Hawaii State Department of Health. (2022). IWS Final Approval Date Report (04/01/2017-04/01/2022).
Hawaii State Department of Health Wastewater Branch. Incinerating Toilets Inc. (2023). Cinderella Comfort Incinerating Toilets. Incinerating Toilets Inc.
https://incineratingtoilets.com/us/product/cinderella-comfort/
Infiltrator. (2023). Advanced Enviro-Septic. Infiltrator Water Technologies. https://www.
infiltratorwater.com/products/presby-environmental/advanced-enviro-septic/
Lekven, C. (2019). Pahala Wastewater Treatment Plant Preliminary Engineering Report. Brown and
Caldwell. https://www.epa.gov/sites/default/files/2020-03/documents/pahala_final_ea_
vol_2_508_2020-02-24.pdf
Mezzacapo, M., & Shuler, C. (2021). 2021 Hawaii Cesspool Hazard Assessment and Prioritization
Tool. University of Hawaii. https://health.hawaii.gov/wastewater/files/2022/01/
priortizationtoolreport.pdf
Mohamed, R. (2009). Why households in the United States do not maintain their septic systems
and why state-led regulations are necessary: Explanations from public goods theory.
International Journal of Sustainable Development and Planning, 4, 143–157. https://doi.
org/10.2495/SDP-V4-N2-143-157
New Zealand Distributors. (2018). AES Homeowners Manual AES (Advanced Enviro-
Septic TM ) Owners Manual (pp. 1–12).
Nuflow Wide Bay. (2015, September 15). Blocked Drains Bundaberg. Nuflow Wide Bay.
https://www.nuflowwidebay.com.au/understanding-the-mysteries-of-septic-
tanks/
Peterson, A. (2010, May 2). Plantation Era Is Gone, and Pahala Lives On: Historic Preservationist
Julia Neal Uses Hammer and Wood to Pull the Community Together. Ke Ola Magazine.
https://keolamagazine.com/community/plantation-era-gone-pahala-lives-on/
Pine Creek Structures. (2023). Excel NE Sun-Mar Composting Toilet. https://www.storageshedspa.
com/sheds/other-products/17759/excel-ne-sun-mar-composting-toilet
Presby Environmental, Inc. (2017). The Presby Wastewater Treatment System Design
and Installation Specifications for Advanced Enviro-Septic ®, Enviro-Septic ®
and Simple-Septic ® Wastewater Treatment Systems Minimizes the Expense
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Protects the Environment Preserves the Site. wwww.PresbyEnvironmental.com
Presby Environmental, Inc. (n.d.). The Next Generation of Wastewater Treatment
Technology Brochure.
ShopTinyHouses. (2023). Sun-Mar Centrex 3000 Composting Toilet System. ShopTinyHouses.Com.
https://www.shoptinyhouses.com/products/sun-mar-centrex-3000-central-composting-
toilet-system
Water Resources Research Center, & Engineering Solutions, Inc. (2008). ONSITE WASTEWATER
TREATMENT SURVEY AND ASSESSMENT. In State of Hawaii, Department of Health.
https://health.hawaii.gov/wastewater/files/2013/06/onsitesurvey.pdf
A-1
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
A
Appendix A - LCC Closure Properties
A-2
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
A-3
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
A-4
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
A-5
Nāʻālehu Individual Wastewater System Preliminary Engineering Report
B
Appendix B - Cost Calculations
A-6
IWS Management Model 2A County In-House Maintenance Cost1
B
Year
0
IWS Installation
Tasks County O&M Staff Cost
Capital Cost/Household
0 Pumping & Hauling equipment $250,000.00 $ 1,470.59
0 Personnel Training $ 50,000.00 $ 294.12
Annual Inspection by & Trouble Calls by County staff – two
1 IWS Operators / Plumbers $ 822.00
2
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
3 Septic sludge pumping & disposal by County staff $ 1,250.00
4
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
5
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
6 Septic sludge pumping & disposal by County staff $ 1,250.00
7
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
8
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
9 Septic sludge pumping & disposal by County staff $ 1,250.00
10
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
11
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
12 Septic sludge pumping & disposal by County staff $ 1,250.00
13
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
14
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
15 Septic sludge pumping & disposal by County staff $ 1,250.00
16
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
17
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
18 Septic sludge pumping & disposal by County staff $ 1,250.00
19
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
20 Absorption bed replacement $ 30,000.00
20 Pumping & Hauling equipment Replacement $250,000.00 $ 1,470.59
21
Annual Inspection by & Trouble Calls by County staff - two
IWS Operators / Plumbers
$ 822.00
Average Annual Maintenance Cost $ 956.44
1 Cost of services are estimated from 2023 USD rates and would increase due to inflation.
A-7
IWS Management Model 2B Outsource Maintenance Cost
Year Tasks Outsource O&M Cost
0 IWS Installation Capital Cost
County Admin
Staff
B
County WWD Admin Personnel Cost for Record Keeping and
administering
Based on $100000/175 = $572
Trouble calls, emergency repairs per IWS per year $ 500.00
1 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
2 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
3 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
4 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
5 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
6 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
7 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
8 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
9 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
10 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
11 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
12 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
13 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
14 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
15 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
16 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
17 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
18 Septic sludge pumping & disposal $ 1,250.00 $ 572.00
19 IWS annual inspection & Trouble Calls $ 550.00 $ 572.00
20 Absorption bed replacement $ 30,000.00 $ 572.00
21 IWS annual inspection (repeat as Year 1) $ 550.00 $ 572.00
Average Annual Maintenance Cost $ 783.33 $ 572.00
A-8
IWS Management Model 3A Operating Permit User O&M Cost
Year Tasks
O&M Cost to
Homeowner/User County Admin Cost
0 IWS Installation 0 Capital Cost
B
O&M Cost to Homeowner / User includes trouble calls $300 + $200 = $500
County admin staff to provide recording keeping, regulation and enforcing Based on $100000/175
1 IWS annual inspection & Trouble calls $ 500.00 $ 572.00
2 IWS annual inspection $ 500.00 $ 572.00
3 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
4 IWS annual inspection $ 500.00 $ 572.00
5 IWS annual inspection $ 500.00 $ 572.00
6 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
7 IWS annual inspection $ 500.00 $ 572.00
8 IWS annual inspection $ 500.00 $ 572.00
9 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
10 IWS annual inspection $ 500.00 $ 572.00
11 IWS annual inspection $ 500.00 $ 572.00
12 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
13 IWS annual inspection $ 500.00 $ 572.00
14 IWS annual inspection $ 500.00 $ 572.00
15 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
16 IWS annual inspection $ 500.00 $ 572.00
17 IWS annual inspection $ 500.00 $ 572.00
18 Septic sludge pumping & disposal $ 1,200.00 $ 572.00
19 IWS annual inspection $ 500.00 $ 300.00
20 Absorption bed replacement $ - $ 30,000.00
21 IWS annual inspection (repeat as Year 1) $ 500.00 $ 572.00
Annual Average Cost $ 733.33 $ 572.00
A-9
IWS Management Model 3B County Voucher O&M Cost
Year Tasks
Trouble call Cost to
Homeowner/User
County Voucher Cost
(present value)
0 IWS Installation 0 Capital Cost
B
County voucher cost: $572 + $300
Based on Admin staff cost $100000/175
1 IWS annual inspection & Trouble calls $ 600.00 $ 872.00
2 IWS annual inspection $ 600.00 $ 872.00
3 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
4 IWS annual inspection $ 600.00 $ 872.00
5 IWS annual inspection $ 600.00 $ 872.00
6 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
7 IWS annual inspection $ 600.00 $ 872.00
8 IWS annual inspection $ 600.00 $ 872.00
9 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
10 IWS annual inspection $ 600.00 $ 872.00
11 IWS annual inspection $ 600.00 $ 872.00
12 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
13 IWS annual inspection $ 600.00 $ 872.00
14 IWS annual inspection $ 600.00 $ 872.00
15 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
16 IWS annual inspection $ 600.00 $ 872.00
17 IWS annual inspection $ 600.00 $ 872.00
18 Septic sludge pumping & disposal $ 600.00 $ 1,572.00
19 IWS annual inspection $ 600.00 $ 872.00
20 Absorption bed replacement $ - $ 30,000.00
21 IWS annual inspection (repeat as Year 1) $ 600.00 $ 872.00
Annual Average Cost $ 600.00 $ 1,105.33
A-10
C
Appendix C - Topography
A-11
A-12
D
Appendix D – USGS Soil Survey
A-13
A-14
E
Appendix E - Geotech Report
A-15
A-16
A-17
A-18
A-19
A-20
A-21
A-22
A-23
F
Appendix F - Typical IWS Layout & Components
A-24
A-25
A-26
SCHEDULE A
ABSORPTION BED & SEEPAGE PIT SIZING
# OF BEDROMS NON-TRAFFIC RATED TRAFFIC RATED SEEPAGE PIT SIZE SEPTIC TANK SIZE ABSORPTION BED SIZE ABSORPTION BED SIZE (SEE NOTE 4)
(SEE NOTE 3) (SEE NOTE 3)
3
1000 GAL.
10'
12'
15'
X
X
X
24'
20'
16'
9'
12'
15'
24'
18'
16'
6'r/J X 12' DEEP
4
1000 OR 1250 GAL.
10'
12'
15'
X
X
X
32'
27'
22'
9'
12'
15'
30'
24'
18'
6'r/J X 15' DEEP
8'r/! X 12' DEEP
5
1250 GAL.
10'
12'
15'
X
X
X
40'
34'
27'
9'
12'
15'
40'
28'
24'
8'r/! X 14' DEEP
6
1250 GAL. PER DWS
10'
12'
X
X
48'
40'
g'
12'
48'
36'
8'r/! X 17' DEEP
(SEE NOTE 2) 15' X 32' 15' 28'
7
1250 GAL. PER DWS
(SEE NOTE 2)
10'
12'
15'
X
X
X
56'
47'
38'
g'
12'
15'
52'
40'
32'
8'r/! X 20' DEEP
NOTES:
1. The request is for Variance from Section 11-62-22 Spacing of Individual Wastewater Systems, Table
II in Appendix D and Section 11-62-31.1(1)(D) where states that one IWS cannot serve more
than 5 bedrooms.
2. For dwellings with more than 5 bedrooms, we request a Variance to base the IWS design on the
DWS water consumption record rather than based on number of bedrooms.
3. Absorption Bed for standard perforated pipe with gravel bed installation (non-traffic rated),
a percolation rate of 2 min./inch is assumed. For gravel-less installation (Infiltrator Chambers)
or traffic rated chambers, 17% reduction is taken for the required area of absorption bed.
4. For sizing of seepage pit, a percolation rate of 1 min/inch is assumed because the soil
condition is likely to be granular or rocky type at that depth.
SETBACK TYPE DESCRIPTION/MIN. PER DOH, TABLE
(SEE NOTE 1)
VARIANCE REQUEST
(SEE NOTE 1)
a DIST. BTW BLDG & SEPTIC TANK /
5' MIN. 2' < "a" < 5'
DIST. BTW PROPERTY LINE
& SEPTIC TANK / 5' MIN. 1' < "b" < 5'
C DIST. BTW BLDG & ABSORPTION BED /
5' MIN. 2' < C < 5'
"d" DIST. BTW PROPERTY LINE
& ABSORPTION BED / 5' MIN. 0 < "d" < 5'
"e" DIST. BTW BLDG & SEEPAGE PIT /
5' MIN. 2' < "e" < 5'
"f" DIST. BTW PROPERTY LINE
& SEEPAGE PIT / 9' MIN. 1' < "f" < 5'
"g" DIST. BTW SEPTIC TANK & ABSORPTION
BED / 5' MIN. 2' < "g" < 5'
DIST. BTW NEIGHBORING ABSORPTION
BEDS / 5' MIN. 1' < "h" < 5'
DIST. BTW NEIGHBORING SEEPAGE
PITS / 12' MIN. 6' < "i" < 12'
A-27
A-28
A-29
A-30
A-31
G
Appendix G - Lava Tube Backfill Detail
A-32
A-33
H
Appendix H – Percolation Test Results
A-34
A-35
A-36
A-37
A-38