HomeMy WebLinkAboutPreliminary Engineering Report (Naalehu WWTP) October 2018
Naalehu Wastewater
Treatment Plant
Preliminary Engineering
Report
Prepared for
County of Hawaii, Department of
Environmental Management
October 2018
1955 Main Street, Suite 200
Wailuku, Hawaii 96793
Naalehu Wastewater Treatment Plant
Preliminary Engineering Report
Prepared for
County of Hawaii, Department of Environmental Management
October 2018
THIS WORK WAS PREPARED BY ME OR UNDER MY SUPERVISION.
April 30, 2020
Signature Expiration Date of the License
iii
Table of Contents
List of Figures .............................................................................................................................................. vi
List of Tables ............................................................................................................................................... vii
List of Abbreviations .................................................................................................................................... ix
1. Introduction .......................................................................................................................................1-1
1.1 Background .............................................................................................................................1-1
1.2 Existing System .......................................................................................................................1-1
1.3 Report Contents ......................................................................................................................1-2
2. Flow and Load Projections ................................................................................................................2-1
2.1 Service Area ............................................................................................................................2-1
2.2 Flow Projections for LCC Conversion Project ........................................................................2-4
2.3 Influent Characteristics ..........................................................................................................2-4
2.4 Influent Mass Loads ...............................................................................................................2-4
2.5 Mass Loads to the Environment via Existing LCCs ...............................................................2-5
3. Effluent Management Options and Regulatory Requirements ......................................................3-1
3.1 Effluent Management Options ...............................................................................................3-1
3.1.1 Ocean Discharge ......................................................................................................3-1
3.1.2 Subsurface Disposal via Injection Wells .................................................................3-1
3.1.3 Water Recycling ........................................................................................................3-1
3.1.4 Land Treatment ........................................................................................................3-2
3.1.5 Drain Field .................................................................................................................3-3
3.1.6 Recommendation .....................................................................................................3-3
3.2 Treatment Requirements .......................................................................................................3-3
4. Wastewater Treatment Evaluations .................................................................................................4-1
4.1 Preliminary Treatment ............................................................................................................4-1
4.1.1 Screening ..................................................................................................................4-1
4.1.2 Influent Flow Measurement .....................................................................................4-2
4.1.3 Influent Flow Sampling .............................................................................................4-2
4.1.4 Preliminary Design of Headworks ...........................................................................4-2
4.1.5 Odor Control ..............................................................................................................4-4
4.2 Aerated Lagoon Treatment System .......................................................................................4-5
4.2.1 Aerated Lagoon Kinetics ..........................................................................................4-5
4.2.2 Aeration in Lagoon Systems ....................................................................................4-5
4.2.3 Aerated Lagoon Configuration .................................................................................4-7
4.2.4 Lagoon Liner .............................................................................................................4-8
4.2.5 Lagoon Cover ............................................................................................................4-9
4.2.6 Lagoon Sludge Management ................................................................................ 4-11
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
iv
4.3 Subsurface Flow Constructed Wetland .............................................................................. 4-11
4.3.1 Denitrification in Subsurface Flow Constructed Wetlands ................................. 4-12
4.4 Disinfection .......................................................................................................................... 4-12
4.4.1 Calcium Hypochlorite ............................................................................................ 4-12
4.4.2 Ultraviolet Light (UV) Disinfection ......................................................................... 4-16
4.4.3 UV System Design Summary ................................................................................ 4-16
4.4.4 Cost Evaluation ...................................................................................................... 4-17
4.4.5 Disinfection Recommendation ............................................................................. 4-17
4.5 Effluent Management .......................................................................................................... 4-17
4.5.1 Design .................................................................................................................... 4-18
4.6 Ancillary Systems ................................................................................................................. 4-21
4.6.1 Water ...................................................................................................................... 4-21
4.6.2 Access Road .......................................................................................................... 4-21
4.6.6 Electrical Systems ................................................................................................. 4-28
4.6.7 Telemetry Systems ................................................................................................ 4-28
4.6.8 Operations Building ............................................................................................... 4-28
4.6.9 Site Fencing ........................................................................................................... 4-28
5. Preliminary Design of Improvements ...............................................................................................5-1
5.1 Site Plan ..................................................................................................................................5-1
5.2 Process Schematic .................................................................................................................5-1
5.3 Design Criteria ........................................................................................................................5-4
5.4 Environmental Benefits ..........................................................................................................5-6
5.5 Cost Estimates ........................................................................................................................5-8
5.6 Future Expansion ....................................................................................................................5-8
5.6.1 Full Buildout Flows ...................................................................................................5-8
5.6.2 Improvements ...........................................................................................................5-8
6. Implementation .................................................................................................................................6-1
7. Alternative Treatment Options Evaluation .......................................................................................7-1
7.1 Option Descriptions ................................................................................................................7-1
7.1.1 Option 1: Aerated Lagoons/Constructed Wetland/Land Application ..................7-1
7.1.2 Option 2: R-1 Treatment/Land Application .............................................................7-1
7.1.3 Option 3: R-1 Treatment/Seasonal Water Recycling ............................................7-2
7.1.4 Option 4: R-1 Treatment and Storage for 100% Water Recycling ........................7-4
7.1.5 Option 5: Maximum Practical Treatment ...............................................................7-6
7.2 Cost Comparisons ...................................................................................................................7-7
7.2.1 Capital Costs .............................................................................................................7-7
7.2.2 Operation and Maintenance Costs ..........................................................................7-7
7.2.3 Recycled Water Sale Proceeds ................................................................................7-8
7.2.4 Life-Cycle Costs .........................................................................................................7-8
7.3 Non-Economic Discussion ......................................................................................................7-9
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
v
7.3.1 Labor Requirements .............................................................................................. 7-10
7.3.2 Operational Complexity ......................................................................................... 7-10
7.3.3 Energy Consumption ............................................................................................. 7-11
7.3.4 Sludge Management ............................................................................................. 7-11
7.4 Living Machine® .................................................................................................................. 7-11
7.5 Septic Tank Alternatives ...................................................................................................... 7-12
7.5.1 Community Septic Tank ........................................................................................ 7-12
7.5.2 Converting LCC to Seepage Pit ............................................................................. 7-12
7.5.3 Leachfield Disposal ............................................................................................... 7-13
7.5.4 Conversion to Individual Wastewater Systems.................................................... 7-13
8. Alternative Site Evaluation ................................................................................................................8-1
8.1 Methodology ............................................................................................................................8-1
8.2 Site Locations .........................................................................................................................8-1
8.3 Criteria .....................................................................................................................................8-3
8.4 Criteria Weighting Factors ......................................................................................................8-7
8.5 Raw Scores ..............................................................................................................................8-7
8.6 Weighted Analysis ...................................................................................................................8-9
8.7 Results .................................................................................................................................. 8-11
8.8 Conclusion ............................................................................................................................ 8-11
9. References ........................................................................................................................................9-1
Appendix A: Flow Projections Summary ................................................................................................... A-1
Appendix B: Cost Estimates..................................................................................................................... B-1
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
vi
List of Figures
Figure 1-1. Existing Naalehu Wastewater System .................................................................................1-3
Figure 2-1. Naalehu LCC Conversion Project .........................................................................................2-2
Figure 2-2. Full Buildout Condition .........................................................................................................2-3
Figure 3-1. Irrigation Demand Assessment ............................................................................................3-2
Figure 4-1. In-Channel Cylindrical Screen ..............................................................................................4-2
Figure 4-2. Headworks .............................................................................................................................4-3
Figure 4-3. Activated Carbon Scrubber (GAC) ........................................................................................4-4
Figure 4-4. High Speed Floating Aerator ................................................................................................4-7
Figure 4-5. Normal Lagoon Configuration Schematic ...........................................................................4-8
Figure 4-6. Floating HDPE Shade Balls ............................................................................................... 4-10
Figure 4-7. Floating shade balls with current and turbulence in reservoir. ...................................... 4-10
Figure 4-8. Subsurface Flow Constructed Wetland Concept ............................................................. 4-11
Figure 4-9. Typical Calcium Hypochlorite Feed System ...................................................................... 4-13
Figure 4-10. Chlorine Contact Tank Configuration ............................................................................. 4-15
Figure 4-11. Gated Pipe in Use ............................................................................................................ 4-19
Figure 4-12. Land Application System Schematic .............................................................................. 4-20
Figure 4-13. NRCS Soil Map .................................................................................................................. 4-23
Figure 4-14. Naalehu Existing Condition .............................................................................................. 4-25
Figure 4-15. Flood Insurance Rate Map ............................................................................................... 4-26
Figure 4-16. Operations Building Preliminary Floor Plan ................................................................... 4-29
Figure 5-1. Preliminary Site Plan .............................................................................................................5-2
Figure 5-2. Recommended Facility Process Schematic ........................................................................5-3
Figure 5-3. Environmental Benefits of Proposed Project ......................................................................5-7
Figure 7-1. Option 1 Schematic Diagram ...............................................................................................7-1
Figure 7-2. Option 2 Schematic Diagram ...............................................................................................7-2
Figure 7-3. Option 3 Schematic Diagram ...............................................................................................7-2
Figure 7-4. Irrigation Demand Assessment ............................................................................................7-3
Figure 7-5. Option 3 Recycled Water Demand Assessment .................................................................7-3
Figure 7-6. Comparison of Irrigation Demands at Naalehu and Kealakehe ........................................7-4
Figure 7-7. Option 4 Schematic Diagram ...............................................................................................7-5
Figure 7-8. Seasonal Storage Reservoir Analysis ..................................................................................7-6
Figure 7-9. Option 5 Schematic Diagram ...............................................................................................7-7
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
vii
Figure 7-10. Life-Cycle Costs of Options .................................................................................................7-9
Figure 7-11. Comparison of Electrical Energy Requirements ............................................................ 7-11
Figure 8-1. Naalehu Site Alternatives .....................................................................................................8-2
List of Tables
Table 2-1. Naalehu LCC Conversion Project Flow Projections ..............................................................2-4
Table 2-2. Summary of Assumed Influent Characteristics ....................................................................2-4
Table 2-3. Projected Influent Mass Loads ..............................................................................................2-4
Table 2-4. Mass Loads to the Environment via Existing LCCs and Newly Accessible Property IWS ...2-5
Table 3-1. Nutrient Water Quality Standards for Class AA Embayments .............................................3-1
Table 3-2. Applicable HAR 11-62 Land Disposal Requirements ..........................................................3-3
Table 4-1. Normal Configuration Aeration and Mixing Requirements ..................................................4-8
Table 4-2. Lagoon Shade Ball Cover Application Parameters...............................................................4-9
Table 4-3. Calcium Hypochlorite Summary ......................................................................................... 4-13
Table 4-4. Chlorine Demand ................................................................................................................ 4-14
Table 4-5. Chlorine Contact Tank ......................................................................................................... 4-14
Table 4-6. UV Disinfection Design Summary ....................................................................................... 4-16
Table 4-7. Estimated Disinfection Costs ............................................................................................. 4-17
Table 4-8. Ultraviolet Disinfection – Advantages and Disadvantages ............................................... 4-17
Table 4-9. Potential Land Application System Tree Species .............................................................. 4-18
Table 4-10. Potential Water Demands ................................................................................................ 4-21
Table 5-1. Preliminary Design Criteria ....................................................................................................5-4
Table 5-2. Environmental Benefits of Proposed Project........................................................................5-7
Table 5-3. Naalehu WWTP Order of Magnitude Capital Cost Estimate ................................................5-8
Table 5-4. Naalehu WWTP Full Buildout Flow Projections ....................................................................5-8
Table 6-1. Implementation Schedule .....................................................................................................6-1
Table 7-1. Summary of Capital Cost Estimates......................................................................................7-7
Table 7-2. Summary of O&M Cost Estimates .........................................................................................7-8
Table 7-3. Summary of Annual Recycled Water Sale Proceeds ............................................................7-8
Table 7-4. Summary of Life-Cycle Cost Estimates .................................................................................7-9
Table 7-5. Comparison of Operational Labor Requirements ............................................................. 7-10
Table 7-6. Comparison of Operator Certification Requirements per HAR 11-61 ............................. 7-10
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
viii
Table 8-1. Environmental, Social and Cultural Criteria .........................................................................8-3
Table 8-2. Location and Site Characteristics .........................................................................................8-4
Table 8-3. Collection System and Service Area Criteria ........................................................................8-5
Table 8-4. Land Use and Availability Criteria ..........................................................................................8-6
Table 8-5. Relative Weighting Factors ....................................................................................................8-7
Table 8-6. Alternatives Analysis – Raw Scores ......................................................................................8-8
Table 8-7. Alternatives Analysis – Weighted Scores ........................................................................... 8-10
Table 8-8. Naalehu Alternative Site Ranking ....................................................................................... 8-11
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
ix
List of Abbreviations
AB aggregate base
AC asphalt concrete
BMP Best Management Practices
BOD5 5-day biochemical oxygen demand
CCH City and County of Honolulu
cfs cubic feet per second
COH County of Hawaii
CFR Code of Federal Regulations
DNA deoxyribonucleic acid
DEM Department of Environmental Management
DOH Department of Health
ELLF end-of-lamp-life
FIRM Flood Insurance Rate Map
FOG fats, oils, and grease
ft3 cubic feet
FTE full-time equivalent
GAC granular activated carbon
gpm gallons per minute
H2S hydrogen sulfide
HAR Hawaii Administrative Rules
HDPE high density polyethylene
HELCO Hawaii Electric Light Company
hp horsepower
hp/Mgal horsepower per million gallons
hr hour
hp-hr horsepower-hour
IWS individual wastewater system
L liter
lbs pounds
LCC large capacity cesspools
LPHO low pressure high output
MBR membrane bioreactor
Mg milligrams
Mgal million gallons
mm millimeter
MSL mean sea level
N nitrogen
NPV net present value
O&M Operation and Maintenance
P Phosphorus
Psi pounds per square inch
RNA ribonucleic acid
ROW right-of-way
SR slow rate
TSS total suspended solids
UIC Underground Injection Control
USEPA United States Environmental Protection
Agency
UV ultraviolet
WQV Water Quality Volume
WWTP Wastewater Treatment Plant
1-1
Introduction
1.1 Background
Naalehu is located in the Kau district of the Island of Hawaii. According to the 2010 United States
Census, the total population for the Naalehu census designated place (CDP) was approximately 866
people.
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. 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 (COH) Department of Environmental
Management (DEM) after a vote by the community.
In 1998, the U.S. Environmental Protection Agency (USEPA) promulgated regulations – 40 Code of
Federal Regulations (CFR) 144.14 – which require the elimination of LCCs. As a result, the County
intends to construct a new sewer collection system located primarily within public right-of-way (ROW)
and replace the existing LCCs with a wastewater treatment plant (WWTP) to address the wastewater
treatment and disposal needs of the Naalehu community.
This report summarizes a proposed WWTP needed in order to treat and dispose of the wastewater
flow that is currently discharged to the LCCs, plus additional sewer connections. While the initial
plan was to construct a community septic tank and convert one of the existing LCCs to a seepage pit,
subsequent evaluation determined this was not feasible, as discussed further in Section 7.5. The
report presents the existing and estimated future flows and loads to the WWTP, the proposed
treatment processes, recommendation for the WWTP upgrades needed to meet the future treatment
needs, and an initial estimate of the cost to construct the improvements project.
1.2 Existing System
Figure 1-1 shows the collection system network and service areas for the LCCs. The LCCs in Naalehu
are numbered 3, 4, and 5; LCCs 1 and 2 are located in Pahala. The collection system is a network of
gravity sewers that discharge to three existing LCCs. 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 about 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 private property, which
transmit wastewater to the LCCs. There are approximately 13 manholes in the sewer system (M&E
Pacific, December 2004). 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 because the existing sewer mains run under homes and in easements
on private property. The County intends to dissolve the majority of the existing easements when the
new collection system is constructed and the easements are no longer needed. The sewer system is
not designed to collect storm water.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 1
1-2
1.3 Report Contents
Section 2 presents flow and load projections for the new WWTP. Section 3 evaluates effluent
management options, and the treatment requirements for the preferred option. Section 4 presents
evaluations conducted to develop the preliminary design of the proposed WWTP, which is presented
in Section 5. An implementation plan is briefly presented in Section 6, followed by discussion of
other treatment options that were considered and evaluated in Section 7. The report concludes with
a WWTP site selection evaluation summary in Section 8.
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P Existing Sewer Manhole (SMH)
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Existing Service Area
SCALE AS SHOWN
JOB NO.: 151494
NAALEHU WASTEWATER TREATMENT PLANT
Existing Naalehu Wastewater System
FIGURE
1-1
Existing Large Capacity
Cesspool (LCC 4)
Existing Large Capacity
Cesspool (LCC 3)
Existing Large Capacity
Cesspool (LCC 5)
NaalehuCemetery
NaalehuElementarySchool
NaalehuPark
NaalehuHongwanji
2-1
Flow and Load Projections
This section summarizes the flow and load projections for the new WWTP.
2.1 Service Area
Figure 2-1 shows the initial service area for the new WWTP. The Kau Community Development Plan
indicates that the sewer system may eventually be expanded to service the entire community, as
shown in Figure 2-2; however, the initial collection system and WWTP presented in this report will
service the properties currently connected to the LCCs or newly accessible to the new collection
system. Although this report does not include design for the full buildout service area, the proposed
WWTP has been designed to accommodate modifications within the proposed site for additional
expansion of the service area in the future.
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Existing Service Area
Newly Accessible to Collection System
Proposed Naalehu WWTP Site
New County Sewer System
SCALE AS SHOWN
JOB NO.: 151494
NAALEHU WASTEWATER TREATMENT PLANT
Naalehu LCC Conversion Project
FIGURE
2-1
NaalehuCemetery
NaalehuPark
NaalehuHongwanji
Proposed NaalehuWWTP Site
NaalehuElementarySchool
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LEGEND
Existing Service Area
Newly Accessible to Collection System
Future Service Area per Kau CDP
Proposed Naalehu WWTP Site
New County Sewer System
SCALE AS SHOWN
JOB NO.: 151494
NAALEHU WASTEWATER TREATMENT PLANT
Naalehu WWTP Full Buildout Condition
FIGURE
2-2
NaalehuCemetery
NaalehuPark
NaalehuHongwanji
Proposed NaalehuWWTP Site
NaalehuElementarySchool
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 2
2-4
2.2 Flow Projections for LCC Conversion Project
Hawaii Administrative Rules (HAR) chapter 11-62 requires proposed county WWTPs be designed in
accordance with their respective county standards. If a county does not have design standards in
place then the design standards of the City and County of Honolulu (CCH) shall be used. The County
of Hawaii has not developed its own standards, so wastewater flow projections were developed using
the CCH current (2017) wastewater standards. Table 2-1 summarizes the flow projections for the
LCC Conversion Project. Details are provided in Appendix A.
Table 2-1. Naalehu LCC Conversion Project Flow Projections
Description Value Peaking Factor
Average dry weather flow 225,000 gallons per day 1.0
Peak day wet weather flow 565,000 gallons per day 2.5 a
Peak hour wet weather flow 490 gallons per minute 3.1
*Derived from Crites and Tchobanoglous, 1998
The WWTP will be designed to accommodate the flow projections shown in the table.
2.3 Influent Characteristics
The properties within the existing service area are primarily residential, but do include several
commercial, apartment, and industrial zoned parcels. The wastewater characteristics of the WWTP
influent are assumed to be similar to typical domestic wastewater. Table 2-2 provides a summary of
the assumed influent characteristics.
Table 2-2. Summary of Assumed Influent Characteristics
Parameter Value
5-day biochemical oxygen demand (BOD5) 300 mg/L
Total suspended solids (TSS) 300 mg/L
Total nitrogen 40 mg/L
Total phosphorus 7 mg/L
2.4 Influent Mass Loads
Table 2-3 summarizes the projected loads to the WWTP, based on the proposed average dry weather
capacity of 225,000 gallons per day and the influent characteristics presented in Table 2-2.
Table 2-3. Projected Influent Mass Loads
Description Value
BOD5 565 lbs./day
TSS 565 lbs./day
Total nitrogen 75 lbs./day
Total phosphorus 13 lbs./day
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 2
2-5
2.5 Mass Loads to the Environment via Existing LCCs
Currently, the connected properties discharge without treatment to three LCCs, as shown in Figure 1-
1. These types of cesspools are a public health and environmental concern because of their
likelihood to release disease causing pathogens and other contaminants, such as nitrate, to
groundwater. In addition, properties that will be newly accessible to the new collection system
currently discharge contaminants to the environment via individual wastewater systems (IWS). The
current annual mass loads to the environment via the existing LCCs based on the flow projections
and assumed wastewater characteristics presented above are summarized in Table 2-4.
Table 2-4. Mass Loads to the Environment via Existing LCCs and Newly Accessible Property IWS
Parameter Annual Load
BOD5 206,000 lbs./year
TSS 206,000 lbs./year
Total N 27,000 lbs./year
Total P 4,700 lbs./year
3-1
Effluent Management Options and
Regulatory Requirements
Effluent management options are evaluated in this section, followed by an assessment of regulatory
requirements for the recommended effluent management system.
3.1 Effluent Management Options
There are few effluent management options available for the community, as discussed below.
3.1.1 Ocean Discharge
The coastal waters in the Naalehu area are classified as “AA” marine waters by DOH. HAR 11-54
does not allow zones of mixing in waters up to a distance of 300 meters (one thousand feet) off
shore if there is no defined reef area and if the depth is greater than 18 meters (ten fathoms). The
water quality criteria for nutrients for Class AA embayments are listed in Table 3-1. 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.
Table 3-1. Nutrient Water Quality Standards for Class AA Embayments
Parameter Geometric mean not to exceed Not to exceed the given value
more than 10% of the time
Not to exceed the given value more
than 2% of the time
Total nitrogen 200 µg/L 350 µg/L 500 µg/L
Ammonia nitrogen 6 µg/L 13 µg/L 20 µg/L
Nitrate + nitrate nitrogen 8 µg/L 20 µg/L 35 µg/L
Total phosphorus 25 µg/L 50 µg/L 75 µg/L
3.1.2 Subsurface Disposal via Injection Wells
Per Hawaii Administrative Rules (HAR), Title 11, Chapter 23, disposal to groundwater via an injection
well is not allowed mauka of the State of Hawaii Department of Health (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 option. 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.
3.1.3 Water Recycling
An irrigation assessment was prepared to assess the viability of water recycling as the primary
effluent management system, assuming the recycled water would be used to irrigate nearby coffee
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 3
3-2
trees or other agricultural crops. Figure 3-1 is a summary of the assessment that shows there is
typically no irrigation demand for three months of the year 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 alone is not a viable primary effluent management
strategy for the community. See Section 7 for additional discussion on potential water recycling.
Figure 3-1. Irrigation Demand Assessment
3.1.4 Land Treatment
The USEPA defines land treatment as “the application of appropriately pre-treated municipal and
industrial wastewater to the land at a controlled rate in a designed and engineered setting. The
purpose of the activity is to obtain beneficial use of these materials, to improve environmental
quality, and to achieve treatment goals in a cost-effective and environmentally sound manner”
(USEPA, September 2006).
Land treatment systems rely on soil and vegetation to achieve treatment objectives, rather than
energy-intensive mechanical equipment. As such, they are considered to be a form of “natural”
treatment (Crites, et. al., 2014).
Land treatment is not a new concept. “Land application of wastewater was the first ‘natural’
technology to be rediscovered (after passage of the Clean Water Act of 1972). In the 1840s in
England, it was recognized as avoiding water pollution as well as returning nutrients in wastewater
back to the land. In the 19th century it was the only acceptable method for waste treatment, but it
gradually slipped from use with the invention of modern devices” (Crites, et. al., 2014).
The soil at the proposed WWTP location are suitable for slow rate (SR) land treatment. The proposed
WWTP effluent management system will make use of an area containing Naalehu medial silty clay
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 3
3-3
loam soil (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. Additional discussion is provided in Section 5.4.
3.1.5 Drain Field
A drain field (i.e., 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 standards indicate approximately 25 acres of leach fields would be required to
accommodate the anticipated flow and provide a 100-percent redundant drain field per the
requirements. There is insufficient soil area available at the proposed WWTP site to construct a
drain field of this size. Therefore, this option is considered to be not feasible.
3.1.6 Recommendation
A slow rate land treatment system is recommended for effluent management, as it is the only
feasible effluent management system available to the community.
3.2 Treatment Requirements
The DOH regulates land treatment as “land disposal” per HAR 11-62. Table 3-2 lists the effluent
requirements for land disposal applicable to the project that were in effect at the time this report
was prepared.
Table 3-2. Applicable HAR 11-62 Land Disposal Requirements
Description Value HAR Reference
BOD5 30 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
4-1
Wastewater Treatment Evaluations
This section presents the evaluations conducted in the conceptual development of the proposed
WWTP.
4.1 Preliminary Treatment
The preliminary treatment system will include screening, influent flow measurement, and influent
sampling equipment.
4.1.1 Screening
Screening is recommended to protect the downstream system operations from large objects, debris,
and rags that can be present in wastewater. Aerated lagoon treatment systems require a minimum
of coarse screens to protect the aeration equipment. The industry trend is towards finer screening
systems that remove greater amounts of debris from the waste stream; screens with 6-millimeter
(mm) (¼-inch) openings are frequently used for activated sludge treatment systems. An aerated
lagoon treatment system can benefit from ¼-inch screening to reduce the amount of floatable debris
on the lagoon shoreline, creating a cleaner facility that is less attractive to birds. Since the Naalehu
WWTP will not be continuously staffed, a screening process requiring minimal attention is desirable.
Furthermore, the screenings volume 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.
4.1.1.1 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 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 4-1 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 two in-channel cylindrical screens, one will be on-line
when the other is redundant, plus a bypass channel with manually cleaned bar rack.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-2
Figure 4-1. In-Channel Cylindrical Screen
4.1.2 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.
4.1.3 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.
4.1.4 Preliminary Design of Headworks
Figure 4-2 shows a plan and section of the proposed headworks. Influent wastewater will enter the
upstream end of the headworks channel. Stop plates will be used to divert the flow to one of the two
the in-channel cylindrical screens, or to the manually-cleaned bar rack. The slide gates will be
designed to allow automatic overflow to the other channels in the event of mechanical screen
failure. The washed and compacted screenings will be deposited in a bag or 55-gallon drum for
periodic disposal. The Parshall flume and automatic refrigerated composite sampler will be located
upstream of the screens. The channels will be covered with fiberglass or aluminum plate to facilitate
foul air collection, which will be conveyed to an odor control unit. In addition, a free-standing roof
structure will be constructed over the headworks to protect the operators and equipment from rain
and sun.
TOAERATEDLAGOONS55 GALLONDRUMINFLUENTBYPASSCHANNELSLIDEGATESPARSHALLFLUMEINFLUENT FLOWMETER ANDAUTOMATIC SAMPLERIN-CHANNELCYLINDRICALBAR SCREENMANUALLY-CLEANEDBAR RACKIN-CHANNEL CYLINDRICALBAR SCREEN55 GALLONDRUMSLIDEGATETOAERATEDLAGOONSINFLUENTPARSHALLFLUMESLIDEGATEFIBERGLASS ORALUMINUM PLATECOVERSFOUL AIRTO ODORCONTROLROOFOUTLINEFIGURESCALE:JOB NO: 150440 PAHALA WASTEWATER TREATMENT PLANTHEADWORKS4-2AA'PLANSECTION A - A'NAALEHU
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-4
4.1.5 Odor Control
A prime 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.
4.1.5.1 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. Package 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 4-3 illustrates the process. The County currently operates GAC scrubbers
at other facilities and purchases the GAC media in bulk to reduce costs.
Figure 4-3. Activated Carbon Scrubber (GAC)
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4-5
4.2 Aerated Lagoon Treatment System
The biological wastewater treatment needs at the Naalehu WWTP will be met by a series of aerated
lagoons. A floating cover will be installed on the last cell to reduce algae in the effluent. The
preliminary design of the aerated lagoon treatment system is developed in this section.
4.2.1 Aerated Lagoon Kinetics
The Naalehu WWTP design is reliant on partial mix aerated lagoon environments to provide the
community’s wastewater treatment needs for the initial buildout condition. Partial mix aerated
lagoon kinetics are described below.
4.2.1.1 Partial Mix Model
Partial mix aerated lagoons are based on the concept of allowing solids to settle in lagoons while
providing only enough aeration and mixing to meet the oxygen requirements of the naturally
occurring micro-organisms in the system. The solids tend to settle in areas of the lagoon that are
subject to less mixing energy, where they anaerobically decompose. Infrequent sludge removal is
required to maintain sufficient lagoon treatment volume.
Removal of BOD5 in partial-mix aerated lagoons depends on the hydraulic detention time. The
design model for partial mixed ponds of equal size in series is (Crites, et. al., 2006):
nnktCo
Cn
)/(1[
1
Where Cn = effluent BOD5 concentration in cell n , mg/L
Co = influent BOD5 concentration, mg/L
k = partial-mix first-order reaction rate constant, day-1
t = total hydraulic residence time in the lagoon system, day
n = number of cells in the series
If the lagoons in a system are of unequal size, then the equation must be applied to each lagoon in
the series. The Ten-States Standards recommends using a value of 0.276 day-1 at 20 ºC for the
reaction rate constant (Great Lakes – Upper Mississippi River Board, 1997).
4.2.1.2 Mixing in Lagoon Systems
The energy required for mixing in aerated lagoon systems is generally provided by the aeration
system. For partial mix systems the aeration system is sized to provide enough oxygen to maintain
aerobic conditions and no more. For mechanical aeration systems energy input of at least 30
horsepower per million gallons (hp/Mgal) of lagoon volume is required to keep solids in suspension
(Rich, 1999).
4.2.2 Aeration in Lagoon Systems
Oxygen requirements in aerated lagoon systems are based on the organic loading entering the cell.
Supplying oxygen at a rate of 1.5 times the BOD5 mass entering the cell has been found to be
sufficient to treat the wastewater. The following equation is used to estimate the oxygen transfer
rate (Crites, et. al., 2006):
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-6
)20()025.1()(Tw
S
Lsw
a
C
CC
NN
Where N = Equivalent oxygen transfer to tap water at standard conditions (lbs/hr)
aN = Oxygen required to treat the wastewater (lbs/hr)
= (oxygen transfer in wastewater)/(oxygen transfer in tap water)
swC = PCss)( = oxygen saturation value of the waste, mg/L
= wastewater saturation value/tap water oxygen saturation value = 0.9
ssC = tap water oxygen saturation value at temperature Tw
P = ratio of barometric pressure at the site to barometric pressure at sea level
LC = minimum dissolved oxygen concentration to be maintained
SC = oxygen saturation value of tap water at 20ºC and 1 atm pressure
wT = wastewater temperature, ºC
Oxygen can be supplied to aerated lagoon systems using mechanical aerators or diffused aeration
systems. Mechanical aerators are commonly rated by the number of pounds of oxygen the units will
supply under standard conditions per horsepower-hour (lbs. O2/hp-hr). Diffused air requirements are
calculated using the following equation (Crites and Tchobanoglous, 1998):
)1440)()()((2 air
oxygen
air OAOTE
WQ
Where airQ = Required air flow (ft3/min)
oxygenW = Oxygen requirements (lbs/day)
AOTE = Actual oxygen transfer efficiency, expressed as a fraction
2O = Fractional percent of oxygen in air by weight (0.2315)
air = Specific weight of air (0.075 lbs/ft3 at 1 atmosphere and 20ºC
The oxygen transfer efficiency of a diffused air system is a function of the air bubble size and the
depth of the water column. Smaller air bubbles result in higher oxygen transfer efficiencies than
larger bubbles, as do diffusers that are set at deeper depths within the water column.
4.2.2.1 High Speed Floating Aerators
High-speed floating aerators are commonly used for aerated lagoon systems. The units consist of a
motor and impeller attached to a float. The units are typically anchored to the lagoon shore using
cables. High-speed floating aerators are designed to pump water from the lagoon and spray it into
the air, allowing oxygen to diffuse into the water droplets. The high-speed floating aerators can be
outfitted with draft tubes to enhance deep water lagoon mixing or anti-erosion plates to ensure water
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
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is drawn from the surface. Figure 4-4 shows a typical high-speed floating aerator, and a photo of a
unit in operation.
Figure 4-4. High Speed Floating Aerator
Advantages of this system include low capital costs, relatively high oxygen transfer efficiency, good
mixing efficiency, and simple operation and maintenance. The chief disadvantage of the system is
the creation of aerosols as the lagoon water is sprayed into the air.
Manufacturers of this type of aerator include Aqua-Aerobics, Aerator Products and Europlec/Aeromix
Systems Inc.
High-speed floating aerators are recommended for the Naalehu WWTP due to their relatively high
oxygen transfer efficiency, low capital cost, and simple operation and maintenance. High-speed
floating aerators are easy to remove from service, and can be easily moved between lagoons or cells,
if needed.
4.2.3 Aerated Lagoon Configuration
The normal operating condition for the Naalehu WWTP will be to operate the four lagoon cells in
series as partial mix environments. Figure 4-5 is a schematic representation of the normal operating
mode. The fourth cell will be outfitted with a floating cover to preclude algae growth. Having four
lagoons will allow the County to take a lagoon out of service for maintenance.
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Figure 4-5. Normal Lagoon Configuration Schematic
Table 4-1 summarizes the results of the aeration and mixing calculations for the normal operational
configuration treating the design average dry weather flow rate of 225,000 gallons per day.
Comparison of the minimum aerator requirements shown in Table 4-1 with the proposed aerator
layout shown in Figure 4-5 reveals that the aerator power supplied exceeds the minimum
requirements. An aerator control system will be provided that will intermittently turn the aerators on
and off in accordance with the operator settings to supply sufficient oxygen to the system.
Table 4-1. Normal Configuration Aeration and Mixing Requirements
Cell Volume
(gal)
Influent BOD5
(mg/L)
Effluent BOD5
(mg/L)
Minimum Aerator
Requirement (hp)
Mixing Density
(hp/Mgal)
1 145,000 300 129 32 30
2 145,000 129 55 14 13
3 145,000 55 24 6 6
4 145,000 Redundant for maintenance purposes
4.2.4 Lagoon Liner
Lagoon liners are required by DOH to prevent wastewater seepage into the ground. The liner will be
exposed to sunlight, so resistance to ultraviolet light (UV) degradation is a key factor in the selection
of the liner material, as is the compatibility of the material with typical domestic wastewater
characteristics and ease of liner maintenance. An 80-mil textured high density polyethylene (HDPE)
geomembrane is recommend for this application.
Textured HDPE is known to have excellent UV resistance, good chemical resistance, and generally is
not affected by fats, oils, and grease (FOG). Maintenance of HDPE requires a specialty contractor
who can complete fusion weld repairs. Unlike smooth HDPE, textured HDPE presents minimal
slipping hazard to operations personnel. Furthermore, the anticipated useful service of an HDPE
liner in typical Hawaii municipal wastewater treatment conditions is 25 to 30 years.
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4.2.5 Lagoon Cover
In the normal operating mode, the final cell in the lagoon series will be covered in order to deprive
algae of sunlight. This will reduce the algae concentration, which can increase total suspended
solids (TSS) levels in the system effluent. The cover should float on the surface of the water, be UV
resistant, suitable for windy environments, and allow for rainwater to pass through the cover to
prevent ponding. A floating shade ball cover is proposed for this installation.
Floating shade ball covers have been used for decades in in the mining, water and wastewater
treatment industries. Figure 4-6 shows the design elements of a typical shade ball, and Figure 4-7
shows how shade balls provide cover on a reservoir. In addition to reducing algae growth, shade ball
covers deter waterfowl from storage ponds. The black, UV-stable HDPE resin has known to withstand
a range of challenging chemical and environmental conditions. Table 4-2 summarizes technical data
for the balls.
Table 4-2. Lagoon Shade Ball Cover Application Parameters
Requirement Description
Algae Control Balls – 90% shade coverage
Temperature 500C to 950C
Wind Resistance Balls ballasted with potable water tested in winds of 120 mph (category 3 hurricane)
Waterfowl Safety Waterfowl do not recognize ball-covered pond as a water body and will not nest on the unstable surface
Lifecycle/Warranty The shade balls are warrantied for 10 years, with an expected resin life of 25+years
Operations and Maintenance
Self-cleaning, self-levelling and require little to no maintenance
Balls will move out of the way of maintenance barge, and can be restrained with booms
Little installation effort required
Precipitation does not affect the cover
Sustainability
Resin is recyclable, paraben free and suitable for drinking water applications
Ballast is potable water
Resin can be made from recycled plastic
Environment
Balls have been installed in chemically harsh environments (mining industry), in drinking water reservoirs, and in tropical locations
Balls reduce algae formation and corresponding disinfectant byproducts in chlorination
applications
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
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Figure 4-6. Floating HDPE Shade Balls
Figure 4-7. Floating shade balls with current and turbulence in reservoir.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-11
4.2.6 Lagoon Sludge Management
Partial-mix aerated lagoons are designed to allow solids to settle to the bottom of the lagoon, forming
a sludge layer. The sludge slowly anaerobically digests in the bottom of the lagoon. The mechanical
aerators in the lagoon maintain an aerobic water cap at the surface of the lagoon that oxidizes any
odors that are released from the anaerobic sludge layer at the bottom of the lagoon. Sludge is
removed infrequently, typically every 20 to 30 years, when the sludge blanket thickness begins to
affect treatment performance or in conjunction with lagoon liner replacement. Aerated lagoon
operators typically monitor sludge blanket thicknesses semi-annually to assess sludge accumulation.
Sludge removal contractors are typically employed to dredge the solids, dewater, and haul to a
landfill for disposal. Sludge from aerated lagoons is typically does not create nuisance odors when
dewatered due to the long residence time in the bottom of the lagoon.
Alternatively, the sludge can be recycled if a permitted land application site is available and the
sludge meets State and Federal requirements for land application or composted with green waste at
a permitted composting facility. However, at the time this report was written there were no permitted
land application sites or composting facilities permitted to take WWTP sludge on the island.
4.3 Subsurface Flow Constructed Wetland
A subsurface flow constructed wetland is recommended to provide additional treatment and
polishing of the aerated lagoon effluent. It is anticipated that the aerated lagoon system will convert
ammonia that is present in the wastewater influent into nitrate via a process called nitrification. A
subsurface flow constructed wetland will remove this nitrogen from the wastewater via a process
called denitrification. Reduction of nitrogen loading through the constructed wetland will decrease
the area required for overland flow effluent management.
Subsurface flow wetlands consist of shallow lined basins that are filled with gravel media and
planted with emergent wetland vegetation. Water is introduced to the gravel media layer and flows
horizontally through the basin. The water level in the wetland is maintained below the gravel surface
at all times. Treatment occurs through physical, chemical, and biological mechanisms as the water
flows horizontally through the gravel media bed. Figure 4-8 is an illustration of the concept.
Figure 4-8. Subsurface Flow Constructed Wetland Concept
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
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4.3.1 Denitrification in Subsurface Flow Constructed Wetlands
Denitrification is a biological process whereby nitrate molecules are transformed into nitrogen gas
molecules by naturally-occurring bacteria. The denitrifying bacteria require five conditions for the
process to occur:
• A place to grow.
• A source of nitrate.
• An anoxic (low-oxygen) environment.
• A source of carbon.
• Adequate water temperature.
The equation used to predict denitrification in subsurface flow constructed wetlands is shown below
(Crites, et.al., 2014). =exp()
where:
= effluent nitrate-nitrogen concentration (mg/L)
= influent nitrate-nitrogen concentration (mg/L)
= temperature-dependent rate constant = 1.00(1.15)() days-1 when T>1°C
= hydraulic residence time (days)
Subsurface flow constructed wetlands are capable of providing additional treatment benefits beyond
nitrogen reduction, such as removal of organic carbon, suspended solids, phosphorus, metals, trace
organics, and pathogens. The additional treatment benefits are not primary design parameters but
should be considered as additional polishing treatment benefits that may be realized for the Naalehu
WWTP.
4.4 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 a calcium hypochlorite system and a UV system were
evaluated.
4.4.1 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 sodium hypochlorite (bleach). Calcium hypochlorite
decomposes in an exothermic reaction if exposed to moisture.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-13
The solid can be directly applied to wastewater at very small WWTPs. Figure 4-9 shows a typical
calcium hypochlorite feed system.
Figure 4-9. 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 4-3 summaries calcium hypochlorite
characteristics.
Table 4-3. Calcium Hypochlorite Summary
Description Characteristic
Transported form Solid
Typical transported concentration 70%
Largest transported volume available 55 lb. pails
Decay Rate Decays 3-5% per year
pH N/A
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
4.4.1.1 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).
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-14
Table 4-4 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.
Table 4-4. Chlorine Demand
Description Flow Chlorine Demand
Average dry weather flow 0.225 mgd 8 - 15 lbs./day
Peak day wet weather flow 0.690 mgd 20 - 38 lbs./day
Peak hour wet weather flow 500 gpm 25 – 47 lbs./day
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). The size
of the chlorine contact tank will need to accommodate a 15-minute contact time for the peak
discharge rate. Disinfection is usually sized for the design peak day wet weather flow. However, for
this application, the peak discharge rate will need to be equal to the peak distribution rate into the
native tree grove slow rate disposal system. To be conservative, one and a half times the design
peak hour flow will be used instead of the peak day wet weather flow. Table 4-5 summarizes the
contact tank dimensions, while Figure 4-10 shows a conceptual contact tank configuration.
Table 4-5. Chlorine Contact Tank
Description Value
Peak discharge rate 750 gpm
Minimum chlorine contact tank 15 minutes
Tank volume required 1,500 cubic feet
Channel water depth 5 feet
Channel width 3 feet
Tank channel total length 100 feet
Tank dimensions including channel walls 14 feet x 36 feet
14'-0"36'-0"Path: P:\Projects\Hawaii, County Of (HI)\151494 COH Naalehu WWTP PER\_CAD\2-FIGURES\PER FiguresFile Name: 151494-FIG-ChlorContactTank Plot Date: October 9, 2018 2:17 PM Cadd User: Richard SellonaFIGURESCALE:
JOB NUMBER:
NAALEHU WASTEWATER TREATMENT PLANT
CHLORINE CONTACT TANK
CONFIGURATION
4-10151494
NONE
WASTEWATER
EFFLUENT
DISINFECTED
EFFLUENT
TO CHLORINATOR
BUILDING
CHLORINE
SOLUTION CHLORINE
CONTACT
CHANNEL
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
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4.4.2 Ultraviolet Light (UV) 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.
4.4.3 UV System Design Summary
A UV disinfection system requires about the same size footprint as chlorine. 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 US, 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 UV300+ 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 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 4-6 summarizes
the size and design criteria for the UV system required to treat the WWTP discharge.
Table 4-6. UV Disinfection Design Summary
Description Value
Peak Hour Wet Weather Discharge 750 gpm
Minimum UV transmittance 65 percent
No. of UV channels 1
Design dose 35,000 µWs/cm2
Disinfection limit 30 e-coli per 100mL
Validation factors 0.98 end of lamp factor
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-17
4.4.4 Cost Evaluation
A summary of capital and life-cycle estimated costs for both chlorination and UV disinfection is
presented in Table 4-7 for comparison.
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 78 percent of the UV
option.
Table 4-7. Estimated Disinfection Costs
Description Chlorination UV System
Capital Cost $240,000 $950,000
Annual Operations and Maintenance* $18,000 $7,500
Life-cycle Cost (30-Year Net Present Value) $700,000 $1,300,000
*Does not include annual labor.
4.4.4.1 Non-Economic Evaluation
Table 4-8 presents a summary of advantages and disadvantages of using an ultraviolet light for
disinfection.
Table 4-8. Ultraviolet Disinfection – Advantages and Disadvantages
Advantages Disadvantages
Effective at inactivating most viruses, spores, and cysts Low dosage may not be effective on some pathogens and
some organisms can repair and reverse the destructive
effects of UV
It’s a physical process, instead of chemical – it eliminated the need to transport, handle, store toxic or
corrosive chemicals
Turbidity and TSS in the wastewater can reduce UV
disinfection effectiveness
No harmful residual compounds created that are toxic to humans or aquatic life Will likely require more call-outs by operators due to alarms caused by “dirty power”.
Shorter contact time (less than a minute) The relative intensity of equipment maintenance requirements, including staffing training and on-island availability.
4.4.5 Disinfection Recommendation
A tablet chlorination system is the recommended disinfection option over the UV system for the
WWTP because it incurs lower capital and lifecycle costs. In addition, tablet chlorination will be
more-reliable than UV due to frequent “dirty power” conditions experience on the island.
4.5 Effluent Management
For effluent management, a slow-rate land application system is proposed. The concept is to
intermittently apply wastewater to crops growing in permeable soils. As the applied water percolates
through the soil matrix or is taken up by the crop, it is treated by physical filtration and by biological
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-18
mechanisms. After an application period or wetting period, the surface dries and oxygen can enter
the soil matrix, which aids aerobic biological treatment. The frequent wetting and drying also
maintains the infiltration rate through the soil surface and minimizes soil clogging. This method of
land application is an effective treatment process for BOD5, TSS, trace organics, phosphorus, metals
and pathogen removal. Furthermore, removal of nitrogen can be significant when the system is
designed and managed for that objective.
4.5.1 Design
The proposed slow-rate system site consists of a net area of approximately 8.5 acres. The 8.5 acres
will be divided into 4 groves of native trees, so that water application will be rotated to a different
grove each day. By using one groove per day the wet/dry cycle will be 1-day wetting and 3-days
drying. The system will be designed to allow a grove to be temporarily removed from service for
maintenance purposes.
The groves will be planted with native Hawaiian trees. Trees grown within the land application area
will need to be water tolerant. Table 4-9 lists a few potential native tree species. Local experts will
be consulted to develop the final list of species.
Table 4-9. Potential Land Application System Tree Species
Common Name Genus Species Salt
Tolerance Water Requirements Rubbish and
Maintenance Preferred Elevation
Milo Thespesia populnea Very Dry to Wet Moderate Low to Medium
Loulu Pritchardia hillebrandii Very Dry to Wet Low Low
Aalii Dodonaea viscosa Very Dry to Medium Low Low to High
Kou Cordia subcordata Very Dry to Wet Moderate Low
Golden Loulu Pritchardia arecina Moderate Dry to Wet Low Low to Medium
Wiliwili Erythrina sandwicensis Moderate Dry to Medium Moderate Low
The distribution system will consist of gated pipe located on the surface. A photo of gated pipe in
operation is shown in Figure 4-11. The gated pipe has small adjustable slots to allow the applied
wastewater to uniformly be distributed over the grove surface. A perimeter fence will be installed to
limit access. Access roads will surround each grove. Figure 4-12 reflects the proposed land
application schematic.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-19
Figure 4-11. Gated Pipe in Use
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JOB NO: 151494
NAALEHU WASTEWATER TREATMENT PLANT
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Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-21
4.6 Ancillary Systems
4.6.1 Water
Potable water is not currently available at the site. The nearest potable water system is located
uphill in town. Table 4-10 provides an initial assessment of the potential water demands at the
WWTP. The water demands are either for process or potable uses. As shown in the table, the
process water demands are significantly greater than the potable demands.
Table 4-10. Potential Water Demands
Description Flow Rate Type Priority
Screenings washer 20 gpm for 10 min/hour
4,800 gpd Process Mandatory with screen
Hose bibs 10 gpm for 20 min/day
200 gpd Process Desirable to maintain facility
Emergency eye wash / shower 20 gal per use Potable Mandatory
Restroom 20 gpd Potable Recommended
To supply water to the WWTP, pipe will be installed from the nearest location in town to supply a 1-
inch water meter with 1 ½-inch backflow preventer.
The on-site water system will be split into two branches, one for process water and one for potable
water. The potable water will service the restroom and emergency eye wash/shower. A second
backflow preventer will separate the process water uses from the potable uses.
4.6.2 Access Road
All weather access will be provided to the WWTP. Access to the site will be provided by connection to
Spur Road. A paved extension to Spur Road is proposed as shown in Figure 5-2. The road will cross
the new drainage channel via a culvert and all-weather maintenance roads will extend into the site to
provide access to and around the various WWTP infrastructure. Additionally, a turn-around area
large enough to accommodate a fire truck will be provided.
Access road pavement options include aggregate base (AB) gravel, asphalt concrete (AC), or
concrete. AB is the lowest cost option but requires the most maintenance. AC pavement is not
recommended for steep (greater than 12 percent) grades. Concrete is the highest cost option but is
the most durable and requires the least maintenance.
The recommended driveway pavement section is 2-inches of AC over 6-inches of aggregate base
course. If any portions of the driveway exceed 12 percent slope, a concrete pavement section is
recommended.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-22
4.6.3 Stormwater Management
The overall goal of stormwater management is to mitigate the adverse impact of new construction on
the environment. Stormwater management can generally be separated into two areas:
1. Stormwater Quantity: management of the quantity of stormwater runoff to prevent
increased flows and volumes from leaving the site and adversely impacting downstream
watercourses.
2. Stormwater Quality: management of the quality of stormwater runoff to prevent
contaminants such as silt, trash, hydrocarbons, heavy metals, and pesticides from
leaving the site through stormwater runoff.
Per the Hawaii County Code, Chapter 27, Section 20, the site drainage plan shall accommodate the
additional runoff caused by the proposed development, within the site boundaries. A preliminary
evaluation of the pre and post development stormwater conditions is described in the following
sections, but a complete analysis will be completed during the design phase to ensure that
requirements of the county code are met or exceeded and that no adverse impact to downstream or
adjacent properties occurs.
4.6.4 Pre-development Stormwater Conditions
The site stormwater can be divided into two categories: 1) on-site flows that are generated at or in
close proximity to the WWTP site and will be directly affected by the plant construction and 2) off-site
flows that are generated at higher elevations and are captured and conveyed by an existing
vegetated diversion channel, which currently outlets at the proposed WWTP site. Though flows from
both sources have the same ultimate discharge point to the southeast of the site, the distinction is
made because a proposed diversion channel will be constructed that will extend and relocate the
outlet of the existing channel. The new outlet will re-join the natural drainage patterns while allowing
for construction of the WWTP.
On-Site
The watershed area that contributes to on-site stormwater flows is located makai of Mamalahoa
Highway. The proposed WWTP site will occupy approximately 25 acres on what is primarily
undeveloped agricultural land, consisting of mostly barren ranch land with trees and brush or cane
fields. The total watershed area contributing to on-site runoff is approximately 123 acres. The areas
contributing to on-site flows are either currently undeveloped or are utilized for agricultural purposes,
and the parcels comprising this area each have a land use zoning classification of either agricultural
or low density residential.
The existing elevations range between 680 to 820 feet above mean sea level (MSL) and slope in a
southeasterly direction at a mild slope of 5 percent or less. The soils in this area are described as
primarily Lava Flows-Kanohina Complex (271), Kanohina-Lava Flows Complex (734) or Medial Silty
Clay Loam (521) by the Natural Resources Conservation Service (NRCS) Soil Survey (Figure 4-13).
These soils are considered to have high surface runoff, however flows reaching the lava area fan out
and are known to percolate through tubes within the lava rock.
The majority of runoff within the on-site watershed areas are overland sheet flow or shallow
concentrated flows that move in a southeasterly direction towards the ocean.
Path: P:\Projects\Hawaii, County Of (HI)\151494 COH Naalehu WWTP PER\_CAD\2-FIGURES\PER Figures File Name:151494-FIG-4-12-NRCS Soil MapPlot Date: October 23, 2018 9:39 AM Cadd User: Irina ConstantinescuFIGURE
DATE: October 23, 2018
SCALE:
JOB NUMBER:
NAALEHU WASTEWATER TREATMENT PLANT
NRCS SOIL MAP
4-12151494
1"=1500'
SCALE IN FEET
0 1500 3000
NAALEHU
WWTP SITE
MAP UNIT
SYMBOL MAP UNIT NAME SURFACE
RUNOFF
HYDROLOGIC
SOIL GROUP
271 Very High D
521 Low B
522 Low B
523 NAALEHU MEDIAL SILTY CLAY LOAM,
20 TO 35 PERCENT SLOPES Medium B
538 NAALEHU MEDIAL SILT LOAM,
0 TO 3 PERCENT SLOPES Very Low B
734 KANOHINA-LAVA FLOWS COMPLEX,
2 TO 10 PERCENT SLOPES Very High C or D
MAMA
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4-13
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-24
Off-Site
The off-site watershed area is located mauka of Mamalahoa Highway and has an agricultural land
use zoning classification. The total watershed area contributing to off-site runoff is approximately
780 acres. This area is well-vegetated, with varying topographical characteristics including a range
of both steep and mild slopes.
Currently, the runoff from the off-site area is collected and conveyed through an existing vegetated
diversion channel. The existing channel starts just below the Naalehu cemetery and collects and
conveys off-site runoff to the south of Mamalahoa Highway, where it discharges flow at an outlet
within the on-site watershed area. In the predevelopment condition, flow from the outlet fans and
dissipates into shallow concentrated flow that runs through the ranch lava-rock land in an easterly
direction. Figure 4-14 conceptualizes the existing drainage system.
4.6.4.1 Flood and Tsunami Hazards
The subject property is designated Zone X, area of minimal flood hazard corresponding to areas
outside of the five-hundred-year flood plain, as indicated on the current September 29, 2017 Flood
Insurance Rate Map (FIRM), Community Panel No. 155166 1925 F. Zone X designations are not
subject to the requirements of the Standards of Floodways, Chapter 27, Section 22 of the Hawaii
County Code. See Figure 4-15 for the Flood Insurance Rate Map.
4.6.4.2 Stormwater Quantity
The on-site and off-site peak stormwater discharges were respectively approximated using the
methods outlined in the current County of Hawaii, Department of Public Works (DPW) Storm
Drainage Standards (Department of Public Works, 1970).
On-Site
The total watershed area contributing to on-site runoff is approximately 123 acres and the estimated
pre-development 50-year 1-hour peak stormwater runoff is 157 cubic feet per second (cfs).
Off-Site
The total watershed area contributing to off-site runoff is approximately 780 acres. The total
estimated pre-development 100-year 1-hour peak stormwater runoff is 3,000 cfs.
4.6.5 Post-Development Conditions
The overall on-site post-development drainage patterns are anticipated to be consistent with the pre-
development condition. The WWTP site is anticipated to bisect runoff into swales that will run
around the site and follow a similar drainage direction to that of the surrounding area. The site
improvements for the WWTP will include grading for the facility, including but not limited to buildings,
lagoon basins, roadways, and parking.
In addition, improvements will include relocation of the existing vegetated diversion channel outlet
makai of the WWTP. The channel alignment will be extended and run along the perimeter of the
WWTP, to divert off-site flows around the WWTP. Figure 5-1 displays the conceptual site plan.
4.6.5.1 Stormwater Quantity
Post-development stormwater is evaluated in terms of on-site and off-site flows.
MAMALAHOA HWYKAMA
O
A
R
DHAAO SPRINGS RDKAALAIKI RDKAMAOA DRKAALUALU RDOHAI RD
NAHELE ST
LOKELANI ST
KILIKA STKAALUALU RDOPUKEA ST
PUAALA PLPOHA ST
2040
1880
1840
1800
1760
1720
1680
1640
1600
1480
14001280
1240
1160
1120
1100
108010601040
1020
1000
980
960
94021002080
2060
1860
182017801740
16601620
1440
13601320
126012001140920
880
2120
2000
1960
192
0
170
0
1520
1420
13801340
1300
1220
1180
860 740680640600580560540
520
720
660
800
760
820780480460440420780
760
740 40038021
40
2020
198
0
1940
1900 15801560 15401500
1460
900
700620
8405002080210010
4
0 2120800740660660 420395010001
395022001
395007016
395008001
395010029±
0 4,5002,250
Feet
Legend
Naalehu WWTP Location
Existing Drainage Ditch
Elev_Contour (20ft)
SCALE AS SHOWN
JOB NO.: 151494
NAALEHU WASTEWATER TREATMENT PLANT
NAALEHU EXISTING WATERCOURSES
FIGURE
4-13
Existing Vegetated
Diversion Channel
Existing Vegetated
Diversion Channel
Naalehu WWTP Site
4-14
Path: P:\Projects\Hawaii, County Of (HI)\151494 COH Naalehu WWTP PER\_CAD\2-FIGURES\PER FiguresFile Name: 151494-FIG-4-14-FIRM Plot Date: October 23, 2018 9:41 AM Cadd User: Irina ConstantinescuFIGURENAALEHU WASTEWATER TREATMENT PLANT
JOB NO: 151494 FLOOD INSURANCE RATE MAP 4-14
SCALE: 1"=2000'
THIS IS AN OFFICIAL COPY OF A PORTION OF THE ABOVE
REFERENCED FLOOD MAP. IT WAS EXTRACTED USING F-MIT
ON-LINE. THIS MAP DOES NO REFLECT CHANGES OR
AMENDMENTS WHICH MAY HAVE BEEN MADE SUBSEQUENT
TO THE DATE ON THE TITLE BLOCK. FOR THE LATEST
PRODUCT INFORMATION ABOUT NATIONAL FLOOD
INSURANCE PROGRAM FLOOD MAPS CHECK THE FEMA
FLOOD MAP STORE AT WWW.MSC.FEMA.GOV.
SCALE IN FEET
0 2000 4000
NAALEHU
WWTP SITE
4-15
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-27
On-Site
The total watershed area contributing to on-site runoff remains the same as the pre-development
condition at approximately 123 acres. However, because the increase in peak flow is a function of
the increase in impervious area associated with improvements, the estimated post-development 50-
year 1-hour peak stormwater runoff is 198 cfs. The WWTP site is anticipated to increase runoff by
roughly 41 cfs.
To ensure that there is no adverse impact on adjacent or downstream properties due to post-
development flows, an on-site drainage system will collect runoff via grated inlets or swales. These
flows will be conveyed to on-site drainage detention systems, such as subsurface linear infiltration or
depressed detention basins, to detain flows and volumes to their pre-development condition.
Additionally, all exposed (not enclosed) treatment processes will be sized to include free-board depth
to accommodate the 24-hour, 100-year storm event. Thus, no stormwater runoff from these areas is
anticipated.
Off-Site
The estimated stormwater runoff flow rate will be the same as the pre-development runoff, which is
approximately 3,000 cfs.
The proposed watercourse diversion will circumvent the WWTP site and will rejoin the natural flow
path to the east, without any additional on-site flow contribution. In addition to not increasing flows
above the pre-development condition, the channel will be designed to comply with the COH Drainage
Standards such that flow conditions at the proposed outlet do not exceed 5 feet per second and to
ensure no negative impact to downstream or adjacent properties (Department of Public Works,
1970).
4.6.5.2 Stormwater Quality
The quality of stormwater leaving the site is also a concern. Stormwater quality degrades with
development and increased impervious surfaces, because various pollutants are introduced into the
stormwater runoff.
The first half-inch of runoff during a storm is referred to as the Water Quality Volume (WQV) or the
“first-flush” volume. This portion of the runoff from a storm contains measurably more suspended
solids plus other contaminants per cubic foot than would be expected in runoff occurring later in the
storm.
Because the anticipated total disturbed area for this project is greater than 1 acre, this project will
trigger compliance with the National Pollutant Discharge Elimination System (NPDES) construction
stormwater permit from the Department of Health (DOH) Clean Water Branch (CWB). To mitigate the
quality of runoff, several best management practices (BMPs) will be considered to satisfy
requirements of the NPDES permit and to ensure that construction activities do not adversely affect
downstream waterways during site development and construction of the diversion channel. BMPs
that will be considered for use during construction include thoughtful project scheduling, flow
routing, and the use of perimeter controls and sediment traps.
Additionally, permanent BMPs will be employed, which include scheduled good-housekeeping, which
will reduce litter and other constituents from being washed into the storm drain system, and
detention basins and underground infiltration facilities that prevent the release of sediment and
other pollutants to downstream waterways or adjacent properties. A full assessment of all available
BMP’s to optimize water quality will be provided during design of the project.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-28
4.6.6 Electrical Systems
It will be necessary to bring electrical power to the WWTP site. It is anticipated that Hawaii Electric
Light Company (HELCO) will bring overhead power lines to the site and supply 480-volt, 3 phase
power to the WWTP via a pole-mounted transformer to a service panel with a meter.
The floating surface aerators will consume the majority of the electricity supplied to the site. An
electrical room will house the electrical gear, plant control equipment and the chlorination system.
Exterior lighting at the site will be limited to manually switched lights at the entrance to the electrical
building and at the headworks area.
A standby power system will be provided in the form of a pad-mounted diesel generator and above-
ground fuel tank with capacity to support three consecutive days of operation. In addition, the
electrical service panel will be equipped with a manual transfer switch and generator receptacle to
allow connection of a trailer-mounted generator in the event of emergency generator failure during
an extended power outage.
4.6.7 Telemetry Systems
A land-line telephone telemetry system with auto-dialer will provide Hilo-based operation staff of
alarm conditions and key operational parameters at the WWTP.
4.6.8 Operations Building
An operations building will be constructed to include the electrical room, chlorinator room, restroom,
and maintenance/storage room, as shown in Figure 4-16.
4.6.9 Site Fencing
The entire WWTP site, including the treatment systems and the land application system, will be
fenced (6-foot high chain link) and posted to prevent unauthorized public access.
MAINTENANCE AND STORAGE
ROOM
SINK AND
COUNTER SPACE
ELECTRICAL
ROOM
8"TYP12' WIDE ROLL-UP DOOR 6'-0"
EMERGENCY
SHOWER AND
EYE WASH DESK AND
WORK SPACE34'-8"46'-8"5'-0" CHLORINATION ROOM
WITH VENTILATION
TABLET
CHLORINATOR
MOTOR
CONTROL
CENTER
6' MIN
CMU
BLOCKS
6'-0"Path: P:\Projects\Hawaii, County Of (HI)\151494 COH Naalehu WWTP PER\_CAD\2-FIGURES\PER FiguresFile Name: 151494-FIG-OpsBldg Plot Date: October 9, 2018 2:20 PM Cadd User: Richard SellonaFIGURENAALEHU WASTEWATER TREATMENT PLANT
JOB NO: 151494 OPERATIONS BUILDING PRELIMINARY FLOOR PLAN 4-14
SCALE: 3/16" = 1'-0"
0 2'8'
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4'12'1' 3'
4-15
5-1
Preliminary Design of
Improvements
The following is a summary of the preliminary design for the proposed Naalehu WWTP.
5.1 Site Plan
The existing parcels are ranch lands. The prevailing grade is in the north-west to south-east direction
at 2 to 3 percent slope. Approximately 17.7 acres of land will be cleared for the construction of the
proposed facility. Figure 5-1 presents a preliminary site plan for the WWTP.
5.2 Process Schematic
Figure 5-2 presents the recommended facilities process schematic.
TMK:
(3)9-5-010:029
MAMALAHOA HIGHWAY
750' RADIUSX
XX
X
X
X
X
X
X
X
X
X
X
XXXXXXXXXXXXXXXXX X X X X
XXXXXX
TMK:
(3)9-5-022:009
LAG
O
O
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X
X
X
XXXXXXXXXXXXXXXXX
X XLAG
O
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LAG
O
O
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LAG
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X
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A
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D
Path: P:\Projects\Hawaii, County Of (HI)\151494 COH Naalehu WWTP PER\_CAD\2-FIGURES\PER FiguresFile Name: 151494-FIG-5-1-WWTP-PreliminarySitePlan Plot Date: October 22, 2018 4:06 PM Cadd User: Irina ConstantinescuFIGURE
DATE: October 22, 2018
NAALEHU WASTEWATER TREATMENT PLANT
151494 PRELIMINARY SITE PLAN 5-1
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
LIMITS
DISPOSAL GROVE
(2.3± ACRES)
DISPOSAL
GROVE
(1.3± ACRES)
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
DISPOSAL GROVE
(2.4± ACRES)
DISPOSAL GROVE
(2.5± ACRES)
HEADWORKS &
ODOR CONTROL
DISINFECTION
OPERATIONS
BUILDING
CULVERT
ACCESS AND
UTILITY EASEMENTS
LOT 1
(14.9± ACRES)
LOT 2 (2.8± 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
PUMP
STATION
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JOB NO: 151494 RECOMMENDED FACILITIES PROCESS SCHEMATIC 5-2
SCALE: NONE
1 2
AERATED LAGOONS
SLOW-RATE LAND
APPLICATION GROVES
3
INFLUENT
AUTOMATIC
SCREEN
BAR
RACK
INFLUENT FLOW METER AND
AUTOMATIC SAMPLER
PARSHALL
FLUME
TABLET
CHLORINATOR
LEGEND
WW FLOW PATH
WW ALTERNATIVE FLOW PATH
AUTOMATIC
SAMPLER
CHLORINE
CONTACT
TANK
FLOW METER
AUTOMATIC
SCREEN CONSTRUCTED
WETLAND
4
COVERED
LAGOON
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-4
5.3 Design Criteria
Table 5-1 provides preliminary design criteria for the facility.
Table 5-1. Preliminary Design Criteria
Description Value
Influent flows:
Average dry weather 225,000 gpd
Peak day wet weather 690,000 gpd
Peak hour wet weather 500 gpm
Influent characteristics
BOD5 300 mg/L
TSS 300 mg/L
Odor control – granular activated carbon
Airflow rate 500 cfm
H2S Inlet concentration 1-10 ppm
H2S removal efficiency 99%
Media type High-capacity carbon
Vessel diameter 3 feet
Vessel height 7 feet
Minimum carbon quantity 680 lbs
Minimum bed depth 3.5 feet
Fan motor 2 hp
Nominal inlet size 8 inches
Mechanical screens
Number of units 2
Type In-channel cylindrical
Screen opening size 0.25 inch (6 mm)
Maximum flow rate capacity Greater than 750 gpm each
Screening washing Integral
Screening compaction Integral
Screening wash water flow 20 gpm
Screening wash water pressure 50 psi
Bypass screen
Type Manually-cleaned bar rack
Bar spacing 1 inch
Rake Interlocking with bars
Screenings receptacle
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-5
Table 5-1. Preliminary Design Criteria continued
Type 55-gallon drum or bags
Screenings volume per million gallons treated 5 ft3/Mgal
Estimated screenings quantity 1 ft3/day
Disposal frequency 1/week
Influent flow metering
Type Parshall flume
Maximum flow capacity Greater than 1,250 gpm
Minimum straight upstream channel section 20 times the throat width
Influent flow sampling Refrigerated automatic composite sampler
Lagoon cells
Number of cells 4
Maximum lagoon temperature 25ºC
Minimum lagoon temperature 20ºC
Freeboard 3 feet
Working water depth 13 feet
Allowance for sludge 3 feet
Total lagoon depth 16 feet
Side slope 3(H) : 1(V)
Working volume of lagoon 1 to 3 1.45 Mgal
Working volume of lagoon 4 1.45 Mgal
Aerators
Type Floating mechanical surface aerators
Cell 1 aerators 40 hp (2 at 20 hp)
Cell 2 aerator 15 hp
Cell 3 aerator 10 hp
Cell 4 aerator 5 hp aspirator style, floating ball cover for algae control
Constructed Wetland
Water temperature 25 degrees C
Aerated lagoon effluent nitrate-N concentration 19 mg/l
Aerated lagoon effluent ammonia-N concentration 1 mg/l
Constructed wetland effluent total N concentration 15.3 mg/l
Total constructed wetland surface area 0.3 acres
Flow path length 60 feet
Hydraulic application width 220 feet
Media depth 24 inches
Media type Medium gravel, D10 = ¾ inch
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-6
Table 5-1. Preliminary Design Criteria continued
Media porosity 38 percent
Percolation prevention system 60 mil high density polyethylene (HDPE) liner
Vegetation Native Hawaiian reeds and/or rushes, species to be determined
Disinfection system
Type Chlorine
Form Calcium hypochlorite tablets
Design chlorine dose 4-8 mg/L
Chlorine contact time 15 minutes minimum
Effluent flow metering
Type Magnetic
Effluent sampler
Type Refrigerated automatic composite
Effluent quality
BOD5 Less than 30 mg/L monthly average
Less than 60 mg/L peak
TSS Less than 30 mg/L monthly average
Less than 60 mg/L peak
Effluent management system
Type Slow-rate land application groves
Number 4
Minimum depth 5 feet
Design percolation rate 0.0095 inches per minute
Design application rate 8 percent of percolation rate
Distribution system Gated pipe
Stormwater containment 100-year, 24-hour storm event
Vegetation Native Hawaiian trees
Stormwater site management 10-year, 1-hour storm
5.4 Environmental Benefits
A well-designed and managed land treatment system limits wastewater application to rates that
minimize adverse impact to groundwater quality. The percolate from the SR land treatment system
is expected to contain less than 1 mg/L of BOD5 and TSS. While the State of Hawaii has not adopted
formal groundwater quality standards, the drinking water standard for nitrate (10 mg/L as N) in the
annual average percolate was used as a performance target to design the land treatment site.
Phosphorus adsorption is excellent in SR land treatment systems, and 99 percent or greater
phosphorus removal is anticipated. Table 5-2 compares the current loads to the environment via the
LCCs and the loads to the environment after the proposed project is implemented via the percolate
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from the land treatment system. Figure 5-3 provides a graphical representation of the
environmental benefits of the proposed project compared to the status quo.
Table 5-2. Environmental Benefits of Proposed Project
Parameter Current Annual Load to
Environment via LCCs
Annual Load to Environment
via Proposed Land Treatment
System Deep Percolate
Reduction
BOD5 206,000 lbs./year 750 lbs./year >99%
TSS 206,000 lbs./year 750 lbs./year >99%
Nitrogen 27,000 lbs./year 4,900 lbs./year 83%
Phosphorus 4,700 lbs./year 48 lbs./year >99%
Figure 5-3. Environmental Benefits of Proposed Project
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5.5 Cost Estimates
An order of magnitude probable capital cost is summarized in Table 5-3. The estimate includes a 20
percent estimating contingency. The detailed cost estimate is included in Appendix B.
Table 5-3. Naalehu WWTP Order of Magnitude Capital Cost Estimate
Description Estimated Construction Cost
Wastewater treatment plant and utilities $14,600,000
Land application system $6,400,000
Drainage improvements $11,400,000
Total construction cost $32,400,000
Engineering, administration, and legal at 25% of construction cost $8,100,000
Total capital cost $40,500,000
5.6 Future Expansion
5.6.1 Full Buildout Flows
Full buildout wastewater flow projections were developed using the Draft Ka’u Community
Development Plan (March 2015) and the CCH’s current (2017) wastewater standards. Table 5-4
summarizes the projected full buildout flows for the community, and Figure 2-2 shows the WWTP full
buildout service area.
Table 5-4. Naalehu WWTP Full Buildout Flow Projections
Description Value Peaking Factor
Average dry weather flow 390,000 gallons per day 1.0
Peak day wet weather flow 1,200,000 gallons per day 2.5*
Peak hour wet weather flow 1,250 gallons per minute 4.6
*Derived from Crites and Tchobanoglous, 1998
5.6.2 Improvements
To accommodate treatment of the increased flow anticipated from the full buildout of the Naalehu
wastewater collection system, the WWTP will require facility upgrades. The recommended upgrades
include headworks and odor control expansion within the existing WWTP site.
Additionally, the lagoon system will require modifications. Lagoon 1 will be converted to a complete
mix aerated lagoon environment to accommodate wastewater treatment needs. In a complete mix
aerated lagoon, sufficient mixing energy is provided to maintain the lagoon solids in suspension
always. A completely mixed aerated lagoon system performs as an activated sludge process without
solids recycle. The higher mixing energy, as compared to a partial mix lagoon, creates greater
opportunity for contact between the naturally-occurring micro-organisms in the lagoon and dissolved
organic matter. As a result, complete mix lagoons provide greater levels of treatment within a
smaller volume than partial mix lagoons. However, facilities must be provided downstream of
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complete mixed lagoons to allow removal of settleable solids from the water column. To provide a
place for solids settling, lagoons 2 through 4 will continue to act as partial mix aerated lagoons
downstream of the complete mix lagoon 1. Lagoon 4 will require no aeration and will continue to be
covered to deprive algae of sunlight and allow suspended solids to settle out of the system effluent.
Based on published soil information, the proposed slow rate groves can accommodate at least a 50
percent flow increase from estimated LCC conversion project flows. Dual-ring infiltrometer testing
will be conducted during design to confirm the actual percolation rate of the site soils. However, in
order to dispose of the full buildout anticipated flow, additional slow rate basins at another location
may have to be identified.
6-1
Implementation
Table 6-1 provides the implementation schedule for the WWTP. The LCCs will be closed following
connection of the existing sewer system to the WWTP.
Table 6-1. Implementation Schedule
Description Milestone
Complete design of WWTP June 28, 2020
Complete construction of WWTP February 28, 2022
Connect existing collection system to WWTP April 17, 2022
7-1
Alternative Treatment Options
Evaluation
Several other treatment alternatives were considered for the Naalehu WWTP, as summarized below.
7.1 Option Descriptions
7.1.1 Option 1: Aerated Lagoons/Constructed Wetland/Land Application
Option 1 consists of an aerated lagoon treatment system with a constructed wetland and
disinfection, followed by land application for effluent management, as described previously
throughout this report. Figure 7-1 is a schematic diagram for Option 1.
Figure 7-1. Option 1 Schematic Diagram
7.1.2 Option 2: R-1 Treatment/Land Application
Option 2 consists of constructing a membrane bioreactor (MBR) or an activated sludge treatment
process followed by cloth media filtration, followed by UV disinfection, to produce recycled water that
meets DOH R-1 recycled water criteria. R-1 recycled water is effluent that has undergone oxidation,
filtration, and disinfection. R-1 is considered the highest grade of recycled water and can be used for
irrigation of golf courses, parks, schools, and all types of agricultural crops. The R-1 treatment
system would be followed by land application as per Option 1. Figure 7-2 is a schematic diagram for
Option 2.
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Figure 7-2. Option 2 Schematic Diagram
7.1.3 Option 3: R-1 Treatment/Seasonal Water Recycling
Option 3 consists of a treatment system similar to Option 2 to produce R-1 recycled water. The
recycled water would be used to irrigate nearby coffee farms and other agricultural uses. In addition,
the recycled water could be used to irrigate parks and school fields in Naalehu. Figure 7-3 provides
a schematic diagram of Option 3.
Figure 7-3. Option 3 Schematic Diagram
A water recycling analysis was prepared to assess the potential seasonal demand for recycled water
produced by the WWTP. Figure 7-4 is an irrigation demand assessment for the Naalehu area based
on published climate data. The graph shows precipitation, estimated evapotranspiration, and the
irrigation demand for each month of the year. As shown in the figure, irrigation is typically needed
from February through October, reaching a peak demand in June. The graph shows that no irrigation
is typically needed between November and January, because precipitation exceeds
evapotranspiration during those months.
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Figure 7-4. Irrigation Demand Assessment
The potential demand for recycled water produced by the Naalehu WWTP was assessed, as shown in
Figure 7-5. The WWTP could potentially provide irrigation water for approximately 43 acres, based
on the peak month irrigation demand in June. During June, all the recycled water produced by the
WWTP would be used on the 43 acres. During all other months the supply of recycled water will
typically exceed the demand, and the excess water would be land applied on the WWTP property as
per the previous alternatives.
Figure 7-5. Option 3 Recycled Water Demand Assessment
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The Naalehu climate makes it possible to recycle only about 46 percent of the annual flow in this
scenario, due to the long wet season and relatively low evapotranspiration rate during the dry
season. This is in stark contrast to the Kailua-Kona area on the leeward side of the island, where the
climate will allow approximately 88 percent of the recycled water produced at the Kealakehe WWTP
throughout the year to be recycled. Figure 7-6 provides a comparison of the irrigation demand in
Naalehu with the irrigation demand at Kealakehe.
Figure 7-6. Comparison of Irrigation Demands at Naalehu and Kealakehe
7.1.4 Option 4: R-1 Treatment and Storage for 100% Water Recycling
Option 4 adds a seasonal storage reservoir, as shown schematically in Figure 7-7.
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Figure 7-7. Option 4 Schematic Diagram
Implementation of a seasonal storage reservoir would make it possible to recycle 100 percent of the
R-1 water produced by the Naalehu WWTP in a typical year. The seasonal storage reservoir would
make it possible to save recycled water produced during the wet season for use during the dry
season. An annual water balance was prepared to assess the seasonal storage reservoir needs for
the Naalehu WWTP. Figure 7-8 provides a summary of the evaluation, and shows recycled water
supply, use, and storage throughout a typical year. As shown in the graph, peak storage of
approximately 30 million gallons (Mgal) would occur during March, and by September the storage
reservoir would be dry and ready for another wet season. Under this scenario it would be possible to
irrigate approximately 95 acres land. The lined, 20-foot-deep storage reservoir would have a water
surface area of approximately 4.7 acres.
Storage of recycled water is not without its challenges. Recycled water contains nutrients that allow
algae to grow. The algae can cause odors if stagnant water conditions are allowed to develop.
Recycled water that is stored in open reservoirs must often be re-treated to improve the water quality
characteristics. Recycled water reservoirs can be equipped with mixers to prevent stagnant water
conditions, and/or be equipped with floating covers to block the sunlight that fosters algal growth.
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Figure 7-8. Seasonal Storage Reservoir Analysis
Implementation of a seasonal storage reservoir and recycling program would not eliminate the need
for a land application system at the WWTP, as described previously. HAR 11-62 requires a disposal
system for all recycled water system, to provide a means for disposal of water that does not meet R-
1 standards or disposal of excess water should the seasonal storage reservoir capacity be exceeded
during an exceptionally wet year.
7.1.5 Option 5: Maximum Practical Treatment
Option 5 consist of implementing advanced wastewater treatment processes that represent
maximum practical treatment. The option is illustrated schematically in Figure 7-9. The process
treatment train consists of a 5-stage Bardenpho activated sludge treatment process, followed by
chemical addition and denitrifying filters to reliably reduce total nitrogen to less than 4 mg/L and
total phosphorus to less than 0.1 mg/L. The treatment processes would be followed by a
disinfection process to create R-1 recycled water. The recycled water produced would be used to
irrigate macadamia nut trees as per Option 3. A seasonal storage reservoir could also be
implemented at additional cost. A land application system would be required as per the previous
Options.
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Figure 7-9. Option 5 Schematic Diagram
7.2 Cost Comparisons
Planning-level cost estimates were prepared for the five options, as described below.
7.2.1 Capital Costs
Table 7-1 summarizes the capital costs associated with the options described above. Additional
detail can be found in Appendix B. The capital costs shown in the table do not include costs
associated with collection system improvements or closure of the existing LCCs.
Table 7-1. Summary of Capital Cost Estimates
Option Name Estimated Capital Cost
1 Aerated lagoons/constructed wetland/land application $35.1 million
2 R-1 treatment/land application $45.0 million
3 R-1 treatment/seasonal water recycling $47.1 million
4 R-1 treatment and storage for 100% water recycling $54.4 million
5 Maximum practical treatment $55.0 million
Comparison of options 1 and 2 shows that providing R-1 treatment instead of the aerated lagoon
and wetland natural treatment system will increase the capital cost by approximately $4.5 million.
Option 3 shows that addition of water recycling to reuse approximately 46 percent of the annual flow
would add an additional $2.1 million in capital costs. Option 4 shows that constructing a seasonal
storage reservoir to recycle 100 percent of the flow would add an additional $7.3 million in capital
costs. Comparison of options 3 and 5 shows that providing maximum practical treatment instead of
normal R-1 treatment would add $7.9 million in capital costs.
7.2.2 Operation and Maintenance Costs
Operation and maintenance (O&M) costs include labor, electricity, chemicals, spare parts, sludge
management, and other costs required to operate and maintain the facility. Table 7-2 provides a
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summary of the O&M cost estimates developed for the options. Additional details can be found in
Appendix B.
Table 7-2. Summary of O&M Cost Estimates
Option Name Estimated Annual O&M Cost
1 Aerated lagoons/constructed wetland/land application $328,000
2 R-1 treatment/land application $1,100,000
3 R-1 treatment/seasonal water recycling $1,106,000
4 R-1 treatment and storage for 100% water recycling $1,122,000
5 Maximum practical treatment $1,493,000
As shown in the table above, Option 1 incurs significantly lower O&M costs than the other options.
The significant cost differential is due to the simple aerated lagoon natural treatment system that
requires less labor, electricity, chemical, and maintenance than the other options.
7.2.3 Recycled Water Sale Proceeds
Options 3, 4, and 5 will produce a marketable product in the form of R-1 recycled water that could be
sold to users for irrigation purposes. The value of recycled water is a function of the value of the
water that it replaces. In general, recycled water is sold to users at a fraction of the price of the
water that is being replaced to provide a financial incentive to use the product. The typical recycled
water price is 25 percent to 90 percent of the cost of the water it replaces.
The Naalehu WWTP will be located at elevation 690 feet MSL. The cost to pump groundwater from
the basal lens to the ground surface at the WWTP is approximately $992 per million gallons. Table
7-3 provides a summary of a recycled water sales assessment of each option, assuming the recycled
water is sold for 90 percent of the cost of the irrigation water it would replace. Additional detail is
provided in Appendix B.
Table 7-3. Summary of Annual Recycled Water Sale Proceeds
Option Name Annual Volume Recycled
(Mgal)
Maximum Annual
Sales Proceeds
1 Aerated lagoons/constructed wetland/land application 0 $0
2 R-1 treatment/land application 0 $0
3 R-1 treatment/seasonal water recycling 39 $34,000
4 R-1 treatment and storage for 100% water recycling 85 $76,000
5 Maximum practical treatment 39 $34,000
7.2.4 Life-Cycle Costs
Life-cycle costs represent the total costs to the community to construct and operate the wastewater
treatment system over a 30-year period. The life-cycle cost evaluation includes capital and O&M
costs, and recycled water sales proceeds as described above. In addition, equipment replacement
allowances are included after 20-years of operation. The life-cycle cost evaluation includes an
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inflationary factor to account for long-term changes in the value of money. The life-cycle costs are
expressed as the Net Present Value (NPV). The NPV represents the amount of money that the
County would need to set aside now in an interest-bearing account to cover all of the costs over the
defined life-cycle. Table 7-4 provide a summary of the life-cycle cost evaluation. Additional detail
can be found in Appendix B.
Table 7-4. Summary of Life-Cycle Cost Estimates
Option Name Estimated Life-Cycle Cost
1 Aerated lagoons/constructed wetland/land application $50.3 million
2 R-1 treatment/land application $71.9 million
3 R-1 treatment/seasonal water recycling $72.7 million
4 R-1 treatment and storage for 100% water recycling $80.1 million
5 Maximum practical treatment $91.1 million
As shown in the table, Option 1 incurs the lowest life-cycle costs, and the other options would all
incur substantially higher costs over the 30-year life-cycle. The life-cycle cost estimates are shown
graphically in Figure 7-10. The operating costs shown in the figure include benefits (i.e., cost
reductions) from recycled water sales where applicable.
Figure 7-10. Life-Cycle Costs of Options
As shown in the graph, the operating cost differential between Option 1 and the other options is the
leading contributor to the lower life-cycle cost of Option 1. The major operating cost differences are
discussed below.
7.3 Non-Economic Discussion
The options are discussed on a non-economic basis below.
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7.3.1 Labor Requirements
The Naalehu WWTP will be operated by the COH DEM, Wastewater Division that is based in Hilo. The
Hilo-based WWTP operators will regularly visit to facility to check the system status, make
operational adjustments, and draw samples for required laboratory testing. In addition,
maintenance personnel will visit the WWTP as needed to conduct equipment and electrical system
repairs.
A major difference between Option 1 and the other options is the frequency of routine operator visits
required, and the number of personnel routinely required. Option 1 will require a single operator to
normally visit the site once per week. The other options will require daily operator visits to conduct
sampling that is required for R-1 compliance. In addition, Options 2 through 5 consist of mechanical
treatment technology that required more operator attention than option 1. Table 7-5 compares the
operational labor differences for the options, as expressed as full-time equivalents (FTEs).
Table 7-5. Comparison of Operational Labor Requirements
Option Name Estimated Operational Labor
Requirement (FTEs)
1 Aerated lagoons/constructed wetland/land application 0.3
2 R-1 treatment/land application 3.7
3 R-1 treatment/seasonal water recycling 3.7
4 R-1 treatment and storage for 100% water recycling 3.7
5 Maximum practical treatment 5.6
7.3.2 Operational Complexity
HAR 11-61 establishes operator certification requirements for WWTPs. The DOH requires that
certified operators operate municipal WWTPs. The larger and/or more complex the wastewater
treatment process, the higher grade of operator required at the facility. Options 1 through 5 were
evaluated for operator certification requirements based on the criteria established in HAR 11-61.
Table 7-6 summarizes the results of the evaluation. As shown in the table, Option 1 would require a
Grade I operator, while the other options would require a Grade IV operator (the highest grade). The
higher requirements for Options 2 through 5 are due to the complexity of the treatment processes
compared to Option 1. In general, the County has difficulty attracting and retaining Grade IV
operators.
Table 7-6. Comparison of Operator Certification Requirements per HAR 11-61
Option Name Operator Certification Level Requirement
1 Aerated lagoons/constructed wetland/land application I
2 R-1 treatment/land application IV
3 R-1 treatment/seasonal water recycling IV
4 R-1 treatment and storage for 100% water recycling IV
5 Maximum practical treatment IV
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7.3.3 Energy Consumption
Figure 7-11 provides a comparison of the electrical energy requirements of the five options. As
shown in the graph, Option 1 will require significantly less electrical energy to operate, due to the use
of natural treatment systems (aerated lagoons) instead of mechanical treatment processes that
require more aeration and process pumping.
Figure 7-11. Comparison of Electrical Energy Requirements
7.3.4 Sludge Management
Sludge management for Option 1 is significantly different than the other options. The partial-mix
aerated lagoon treatment system allows wastewater solids to accumulate at the bottom of the
lagoon, forming a sludge blanket that slowly anaerobically digests. Sludge removal is infrequent,
typically on the order once every 20 years. The resulting solids are well-digested and inoffensive due
to the long retention time in the lagoons.
Options 2 through 5 would require an aerobic digester to stabilize and store waste solids from the
activated sludge treatment process. The solids would need to be dewatered and trucked to a landfill
on a weekly basis.
7.4 Living Machine®
Living Machine® technology was suggested during community outreach meetings. Living Machine®
is a proprietary technology by Worrell Water Technologies that incorporates aerated tanks planted
with vegetation to provide an attractive wastewater treatment process. In colder climates the
aerated tanks are housed in a greenhouse for protection. In addition, subsurface flow wetlands with
continuous and/or batch flow can be included in the process to provide desired treatment.
The Living Machine® technology has been implemented in “green” buildings like the San Francisco
Public Utilities Commission building, the Port of Portland Headquarters, and others. Review of the
company’s website did not reveal any municipal projects completed on the scale of what would be
needed for Naalehu. Therefore, the technology is considered to be not feasible.
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It should be noted that the proposed non-proprietary treatment system (aerated lagoons and
subsurface flow wetland) uses essentially the same natural treatment processes as the Living
Machine®, but on a municipal scale.
7.5 Septic Tank Alternatives
A previous assessment recommended installation of a community septic tank and repurposing one
of the existing LCCs to serve as a seepage pit (SSFM, July 2007), in accordance with Alternative 1
proposed to the community by the County in 2004 (County of Hawaii, November 5, 2004). This and
other options that have been raised during the community outreach process that incorporate septic
tank technology are discussed below.
7.5.1 Community Septic Tank
The effectiveness of a septic tank is directly related to the amount of hydraulic detention time
provided by the tank volume. The previous study (SSFM, July 2007) suggested a 24-hour detention
time would be adequate. Applying the current flow projections for the project indicate a 230,000-
gallon tank would be appropriate if this criterion is used. However, for large community septic tanks
it has been found that longer detention times are needed to optimize treatment performance, avoid
the need for frequent septage pumping, and to account for peak flow rates that are developed by
community wastewater collection systems. Applying appropriate design criteria (Crites and
Tchobanoglous, 1998), to the project results in the need for an 966,000-gallon tank, which would
require pumping on a 3-year interval. The area required for an appropriately-sized community septic
tank would be approximately ¼ acre.
The use of a community septic tank would require the DOH to issue a variance to HAR 11-62-23.1,
which requires WWTPs with design capacities greater than 100,000 gallons per day to produce
effluent containing less than 30 mg/L of both BOD5 and TSS; septic tanks are not able to produce
effluent of this quality. A secondary treatment process is needed to comply with the effluent quality
requirements contained in the DOH regulations. The County would need to reapply for the variance
every 5-years, and if not renewed then secondary treatment would need to be provided.
Additionally, odors from a community septic tank present a significant concern. A septic tank is an
anaerobic treatment process that produces hydrogen sulfide, reduced sulfur compounds, and other
odorous gases. Odors emanating from septic tanks at individual residences are typically dispersed
to the atmosphere throughout the community via the household plumbing roof vents. A community
septic tank would concentrate the community’s emissions to a single point source that would require
foul air collection and treatment to avoid nuisance odor conditions. A dual-stage scrubber capable of
treating approximately 4,300 cubic feet per minute of foul air would be required to avoid nuisance
odor conditions. The dual-stage scrubber would consist of a biotrickling filter, followed by a granular
activated scrubber.
7.5.2 Converting LCC to Seepage Pit
A previous study (SSFM, July 2007) suggested that the existing LCC located on the County-owned
parcel TMK 9-5-024:011 could be converted to a seepage pit that would be regulated by DOH as an
injection well. HAR 11-23-07 allows injection wells located mauka of the UIC line that were in
existence prior to July 6, 1984 to continue to operate. However, the flow to the wells cannot
increase, nor can a new well be constructed. Therefore, the earlier plan to convert the existing LCC
to a seepage pit is not feasible for the following reasons:
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Closing the other two LCCs in the community that are located on private property would
increase the flow to the LCC (converted to a seepage pit that is regulated as an injection well)
that is located on County property.
Percolation testing conducted on the existing cesspool on County-owned parcel
revealed a disposal capacity of 3 gpm, (Masa Fujioka & Associates, February 9,
2009) or about 4,320 gpd. Cleaning the cesspool would likely increase the capacity
somewhat, but the resulting capacity would be far below what the community needs.
HAR 11-62-25 requires new and proposed effluent disposal systems to have a backup
disposal system capable of handling the peak flow. A second seepage pit cannot be
constructed to comply with the regulatory requirement because the site is located mauka of
the UIC line. If the existing seepage pit were to fail then a replacement cannot be
constructed.
The Kau Community Development Plan requires the County to provide for eventual
construction of sewers throughout the community. Providing sewers for the entire
community will increase wastewater flows considerably, as presented in Section 5.
Increasing flow to the existing LCC (converted to a seepage pit) would not be allowed.
Therefore, the use of the existing LCC as a disposal system could prevent the County from
providing the community’s desired future wastewater needs.
Act 131 (18), signed into law on July 5, 2018, prohibits DOH from issuing permits “for the
construction of sewage wastewater injection wells unless alternative wastewater disposal
options are not available, feasible, or practical.”
For these reasons, converting the existing LCC to a seepage pit is considered to be not feasible.
7.5.3 Leachfield Disposal
Leachfields are effluent disposal systems consisting of buried gravel-filled absorption trenches.
Significant treatment occurs as septic tank effluent percolates through the soil surrounding the
leachfield trenches. Leachfields are an integral part of residential septic systems, and DOH has
established trench design criteria applicable to both residential and municipal-scale leachfields. In
particular, HAR 11-62-34 requires trenches to be sized based on bottom area only. Application of
the DOH criteria to the project yields a need for at least 25 acres of land to satisfy DOH hydraulic
loading rate and redundancy requirements. Achieving even distribution of effluent over a leachfield
of this size would be challenging at best. Therefore, leachfield disposal for the project is considered
to be not feasible.
7.5.4 Conversion to Individual Wastewater Systems
The concept of a community wastewater system could be abandoned, and all houses be required to
construct individual wastewater systems comprised of a septic tank and leachfield. However, many
of the lots in the community are small (less than 10,000 square feet) and significantly improved,
making the feasibility of constructing individual wastewater systems on every lot uncertain. HAR 11-
62-34 allows construction of seepage pits where there is insufficient land area to install absorption
trenches (i.e., a leachfield), but prohibits construction in soils having percolation rates slower than
10 minutes per inch or where rapid percolation through such soils may result in contamination of
water-bearing formations. The soils in the community are classified as Naalehu medial silty clay
loams in the National Resource Conservation Service soil survey. Borings at County-owned parcel
TMK 9-5-024:011 revealed soil depths varying from 2 feet to 27 feet deep over hard basaltic rock or
clinker. Lots with inadequate soil depth for conventional soil absorption trenches would be required
to import fill soil to create elevated mound systems in accordance with HAR 11-62-34 to achieve
adequate soil depth. Residents without sufficient space could potentially install seepage pits if
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suitable subsurface geology could be located. Conversion to individual wastewater systems is
considered to be not feasible due to the high level of uncertainty associated with site conditions on
the small lots.
8-1
Alternative Site Evaluation
Thirty-two sites were evaluated as potential locations for the Naalehu WWTP. Each site was
assessed for twenty-one criteria, in four broad categories: environmental, social and cultural;
location and site; land use and availability; and collection system and service area.
8.1 Methodology
The site evaluation was performed according to the following process:
1. Potential sites for the Naalehu WWTP were initially identified by the Department of
Environmental Management. Additional sites were identified based on feedback from the
Naalehu community obtained during Community Outreach meetings that took place in April
2018.
2. Four general categories and twenty-one criteria were established and defined for the
analysis.
3. Six “fatal flaw” conditions were identified. Sites with one or more fatal flaw were eliminated
from further consideration.
4. Relative weighting factors were established for each category and criteria.
5. Sites were mapped using GIS. Data such as soil type, location of subsurface and surface
water, topography, zoning and prevailing wind direction were determined.
6. Each site was evaluated and scored for the twenty-one criteria.
7. A weighted ranking was determined for each site, based on the weighting factors established
in Step 4.
8. A preferred site was identified, based on the weighted high score.
8.2 Site Locations
Ownership, location, and proximity to the existing LCCs for all siting alternatives considered is
illustrated in Figure 8-1.
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8.3 Criteria
The criteria used for the analysis are presented for each of four categories in Tables 8-1, 8-2, 8-3
and 8-4. A score was assigned to each criterion based on definitions included in the tables. A score
of five represents a preferred or positive condition, and a score of one a less preferred or negative
condition. A score of zero indicates a fatal flaw; six fatal flaw conditions were identified during the
analysis are identified in the corresponding table.
Table 8-1 outlines the environmental, social, and cultural criteria considered in the analysis.
Table 8-1. Environmental, Social and Cultural Criteria
Criteria Scoring and Definitions
5 4 3 2 1 0 = Fatal Flaw
Presence of or proximity to archaeological/cultural sites
No known or suspected sites Confirmed or suspected sites and mitigable
No information available Suspected sites and mitigation ability unknown
Confirmed sites and mitigation ability unknown
Confirmed sites and unmitigable
Proximity of treatment
units to existing occupied buildings
More than 1000
ft. from any occupied building
Between 50 and
1000 ft. from non-school building
Between 50 and
1000 ft. of school
Less than 50 ft
from any occupied building
Prevailing wind direction Site is downwind of most of the community
Site is central Site is upwind of most of the community
Biology Endangered or
threatened species not present
Presence of
endangered or threatened species unknown
Endangered or
threatened species known to be present
Endangered or
threatened species known to be present and unmitigable
Visual impact Natural visual mitigation (hill, berm,
vegetation,
remoteness) exists
Visible location, mitigable with trees or other
engineered
buffers
Visible location, unmitigable
Contamination from prior
land use
No suspected
industry-related contamination issues
Presence of
contamination unknown
Suspected or
confirmed contamination issues
Previously disturbed or
developed
Yes Partial No previous
development or disturbance
The circumstance where a cultural or historical site is known to exist within the treatment facility
footprint and mitigation to relocate, protect, or preserve that site is not possible, was identified as a
fatal flaw condition.
From an environmental perspective, the presence of endangered or threatened species was
considered negative. A site previously disturbed or developed was viewed as positive, unless
contamination from a previous land use was suspected.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-4
Considerations specific to social impact include proximity to occupied buildings (including
residences, school, commercial establishments and others), prevailing wind direction, and visual
impact. Based on community feedback received in April 2018, locations near Naalehu Elementary
School were considered less favorable than other locations.
Table 8-2 outlines the location and site characteristics considered in the analysis.
Table 8-2. Location and Site Characteristics
Criteria Scoring and Definitions
5 4 3 2 1 0 = Fatal Flaw
Parcel size More than 14.9 acres Less than 14.9 acres
Subsurface Geology
Good soil and in sufficient amounts in area of parcel useable
for disposal
Good soil but over limited area and disposal modification
required or
marginal soil in area of parcel useable for disposal
No soil in area of parcel useable
for disposal or no
clinker layer for drainage
Topography Gentle slopes (less than 8%) Moderate slopes (8% - 18%) or localized
high/low points
Steep slopes (18% - 20%) Extreme slopes (greater than 20%)
Proximity to water well Outside of both 1000 ft. radius and upgradient
influence zone of
any well
Outside of 1000 ft. but suspected within
upgradient
influence zone of non-potable well
Within 1000 ft. or within upgradient
influence zone of
non-potable well
Within 1000 ft. or within
upgradient
influence zone of potable well
Presence of lava tubes None Possible or
unknown
Known
Proximity to surface water, intermittent stream or
coast line
Treatment and disposal more
than 500 ft.
away
Treatment and disposal
between 50 to
500 ft.
Treatment and disposal less
than 50 ft. away
Flood control / drainage No risk of
flooding
Flood risk known
and mitigatable
Flood risk
unknown
Prone to flooding
or within flood
zone
Vehicle access Vehicle access currently exists Existing easement, but
new road or significant road upgrades required in or via county/private
right if way
Existing easement, but
new road or significant road upgrades required in or via state right-of-
way
No current vehicle access or
easement, access legally restricted, or significant obstruction to
access
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-5
Table 8-2. Location and Site Characteristics
Criteria Scoring and Definitions
5 4 3 2 1 0 = Fatal Flaw
Power and potable water
availability
Utilities currently
available at property line and within 400 ft. of site, no new
easement
required, no known significant obstructions (i.e.
- culverts,
streams, cultural sites)
Utilities
available within 400 yds. of property or unknown
Potable water
and/or power not currently available within 400 yds. of
property and/or
significant obstruction to utility construction
Three fatal flaw conditions were identified for the location and site characteristics category in Table
8-2:
Sites less than 14.9 acres in size, which is the least amount of land needed for treatment,
disposal, and future growth.
Average slopes greater than 20 percent, which significantly increase the cost of construction
and limit design options.
Location within a 1000-foot radius surrounding a potable water well, which is prohibited by
HAR 11-62 for the protection of drinking water in the State of Hawaii.
Table 8-3 outlines the collection system and service area characteristics considered in the analysis.
Table 8-3. Collection System and Service Area Criteria
Criteria Scoring and Definitions
5 4 3 2 1
Distance from LCC collection
area
Parcel is adjacent
to existing LCC or less than 0.25 miles away
Parcel is 0.25-0.5
mile away from existing LCC
Parcel is 0.5-1.0
miles away from existing LCC
Parcel is 1.0 – 1.5
miles away from existing LCC
Parcel is more than
1.5 miles away from existing LCC
Gravity flow possible or pumping required Gravity flow possible Pumping required for wastewater transmission from collection area to site
Number of properties newly accessible Central village commercial area becomes
accessible
Additional individual residential
properties become
accessible outside of LCC service area
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-6
A site location requiring large transmission distances of more than two miles are less preferable due
to both initial capital cost and future operations and maintenance requirements. Similarly, sites
where wastewater can flow via gravity from the collection area are preferable to those requiring a
pump station.
Newly accessible refers to properties within the service area that are not currently connected to the
LCC, but will become accessible to the County-owned sewer system when the collection lines are
relocated into the roadways fronting the property. Hawaii County Code requires connection of these
properties once the new collection system is constructed, and their individual wastewater systems
(cesspools or septic tanks) properly removed from service. All individual cesspools in the State of
Hawaii must be converted or closed by the year 2050.
In accordance with the Kau CDP, locations that enhanced the ability to serve commercial facilities
were considered favorable in the analysis.
No fatal flaws were identified for the Collection System and Service Area category.
Table 8-4 outlines the characteristics considered in the analysis.
Table 8-4. Land Use and Availability Criteria
Criteria Scoring and Definitions
5 4 3 2 1
Current zoning and land use WWTP currently permitted in zoning without Special
Permit
WWTP possible onsite Special Permit required
WWTP not recommended on site
Land availability Owner willing and able to sell or land currently
government (state, county) owned
Subdivision required or friendly condemnation
required
Difficult or lengthy approval process expected or owner
willingness to sell unknown
Owner unwilling to sell or unfriendly condemnation of
land required (private corporate owner)
Owner unwilling to sell or unfriendly condemnation
required (private family owner)
Although public facilities are permitted in any zoning in the County of Hawaii, construction of a
wastewater treatment facility requires a Special Permit within some zones. Based on community
feedback received in April 2018, locations necessitating condemnation of private, family-owned
properties were considered much less favorable than locations with a willing seller or currently
government-owned. No fatal flaws were identified for the land use and availability category.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-7
8.4 Criteria Weighting Factors
To consider the relative importance to the categories and criteria, each was assigned a weighting
factor for the analysis. Weighting allows for appropriate consideration of all factors - both the
technical and non-technical - associated with siting. Relative weighting is summarized in Table 8-5.
Table 8-5. Relative Weighting Factors
Category Category Weight Criteria Criteria Weight
Environmental, social and cultural 35% Presence of and/or proximity to archaeological/cultural sites 25%
Proximity of treatment units to existing occupied buildings 25%
Prevailing wind direction 25%
Biology 10%
Visual impact 5%
Contamination from prior land use 5%
Previously disturbed or developed 5%
100%
Location and site characteristics 35% Parcel size 25%
Soils type 25%
Topography 15%
Proximity to water well 10%
Presence of lava tubes 8%
Proximity to surface water, intermittent stream or coast line 6%
Flood control / drainage 5%
Existing vehicle access 3%
Power and potable water availability 3%
100%
Collection system and service area 15% Distance from LCC collection area 50%
Gravity flow possible or pumping required 30%
Number of properties newly accessible 20%
100%
Land use and availability 15% Current ownership 55%
Current zoning and land use 45%
100%
8.5 Raw Scores
For the thirty-two sites identified in Figure 8-1, raw scores were assigned for each of the twenty-one
criteria according to the definitions in Section 8.3. The results are presented in Table 8-6.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-8
Table 8-6. Alternatives Analysis – Raw Scores
Category Criteria Site Raw Score
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Environmental, social
and cultural
Presence of and/or proximity to archaeological/cultural sites a FF
Proximity of treatment units to existing occupied buildings
Prevailing wind direction
Biology
Visual impact
Contamination from prior land use
Previously disturbed or developed
Location and site
characteristics
Parcel size b FF FF FF FF FF FF FF FF FF
Soils type c FF FF FF FF FF FF FF FF FF FF FF
Topography d FF
Proximity to water well e FF
Presence of lava tubes
Proximity to surface water, intermittent stream or coast line
Flood control / drainage
Existing vehicle access
Power and potable water availability
Collection system and
service area
Distance from LCC collection area
Gravity flow possible or pumping required
Number of properties newly accessible
Land use and availability Current zoning and land use
Current ownership
Raw score totals (maximum possible = 105) FF FF FF FF FF 75 72 FF FF FF FF 78 FF FF FF FF FF 65 65 FF 79 FF FF FF FF 68 68 FF 77 81 77 75
a Fatal flaw condition for Site 1.
b Fatal flaw condition for Sites 2,10,11,14,22,23,24,25,and 28.
c Fatal flaw condition for Sites 1,4,5,8,9,13, 14,15,16, and 22.
d Fatal flaw condition for Site 20.
e Fatal flaw condition for Site 17.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-9
The scoring was completed based on the best information available at the time of writing. Changing
circumstances can and do affect the scoring over time. Circumstances that have affected the
ranking of sites in Naalehu include:
The identification of an unmitigable cultural site at Site 1 during archaeologic investigation. Community preference for a larger than regulated buffer between the elementary school and
treatment facilities during community outreach meetings.
Willingness of Site 29 owners to sell.
Elimination of injection wells as a disposal method for consideration resulting in larger area
requirements for disposal.
Inadequate soil permeability conditions for disposal identified during investigations of Sites
2, and 24.
Subsurface conditions not conducive to disposal identified during exploratory geotechnical
drilling on Site 13.
As indicated in Table 8-6, fatal flaw conditions were identified for the following 19 sites:
Sites 2,10,11,14,22,23,24,25, and 28 (due to site size).
Sites 1,4,5,8,9,13, 14,15,16, and 22. (due to subsurface or soil conditions).
Site 1 (due to unmitigable archaeologic/cultural site).
Site 20 (due to extreme slopes). Sites 17 (area within 1000 ft of a potable water well).
These affected areas were removed from further analysis.
8.6 Weighted Analysis
The weighted analysis is presented in Table 8-7.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-10
Table 8-7. Alternatives Analysis – Weighted Scores
Category Criteria Site Raw Score
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Environmental, social
and cultural
Presence of and/or proximity to archaeological/cultural sites a FF 0.25 0.75 0.75 1 0.75 0.75 0.75 0.75 0.75 1 1 0.75 0.75
Proximity of treatment units to existing occupied buildings 1.25 0.75 0.75 1.25 1.25 1.25 0.75 0.5 1.25 0.5 1.25 1.25 1.25
Prevailing wind direction 0.25 0.75 1.25 1.25 1.25 1.25 0.75 1.25 1.25 0.25 1.25 1.25 1.25
Biology 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
Visual impact 0.15 0.15 0.15 0.25 0.15 0.15 0.15 0.15 0.25 0.15 0.25 0.15 0.25
Contamination from prior land use 0.15 0.15 0.15 0.25 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15
Previously disturbed or developed 0.15 0.15 0.25 0.15 0.15 0.15 0.25 0.15 0.15 0.25 0.25 0.25 0.25
Location and site
characteristics
Parcel size b FF 1.25 1.25 FF FF 1.25 1.25 FF 1.25 1.25 1.25 FF FF FF FF 1.25 1.25 FF 1.25 1.25 1.25 1.25
Soils type c FF FF FF FF 1.25 0.75 FF FF 0.75 0.25 FF FF FF 0.25 0.25 1.25 FF 1.25 0.25 1.25 1.25 1.25 1.25
Topography 0.75 0.45 0.75 0.75 0.15 0.15 FF 0.45 0.45 0.45 0.75 0.75 0.45 0.45
Proximity to water well d 0.5 0.5 0.5 0.5 FF 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Presence of lava tubes 0.08 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24
Proximity to surface water, intermittent stream or coast line 0.3 0.3 0.3 0.3 0.3 0.3 0.18 0.3 0.3 0.3 0.3 0.18 0.18
Flood control / drainage 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15
Existing vehicle access 0.15 0.15 0.15 0.09 0.15 0.15 0.15 0.09 0.09 0.15 0.09 0.15 0.09
Power and potable water availability 0.15 0.15 0.15 0.03 0.03 0.03 0.15 0.09 0.03 0.15 0.09 0.09 0.03
Collection system and
service area
Distance from LCC collection area 1.5 2 2 1 0.5 0.5 2 2 1 2.5 2 1.5 1.5
Gravity flow possible or pumping required 1.5 0.3 0.3 0.3 0.3 0.3 0.3 1.5 0.3 1.5 0.3 0.3 0.3
Number of properties newly accessible 0.6 0.6 1 1 0.6 0.6 1 0.6 0.6 0.6 1 1 1
Land use and availability Current zoning and land use 1.35 1.35 2.25 1.35 1.35 1.35 2.25 1.35 1.35 1.35 1.35 1.35 1.35
Current ownership 2.75 1.65 1.65 2.2 2.75 2.75 2.2 1.65 2.75 0.55 2.2 1.65 1.65
Weighted score totals (maximum possible = 5 FF FF FF FF FF 3.61 3.31 FF FF FF FF 3.79 3.62 FF FF FF FF 3.15 3.15 FF 3.70 FF FF FF FF 3.77 3.37 FF 3.68 4.19 3.79 3.78
Naalehu Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-11
8.7 Results
The results of the analysis are presented in Table 8-8. Nineteen sites were identified as having fatal
flaws and the remaining thirteen were ranked in accordance with the overall weighted score.
Table 8-8. Naalehu Alternative Site Ranking
Rank Site
1 30
2 31
3 32
4 21
5 12
6 6
7 29
8 7
9 27
10 (tie) 16
10 (tie) 18
12 26
The top three sites for the Naalehu WWTP are:
1. Site 30 (TMK 9-5-007:016)
2. Site 31 (TMK 9-5-008:001)
3. Site 32 (TMK 9-5-008:001)
Site 30 is preferred to the second and third ranked sites for the following reasons:
Preliminary Archaeological investigations for Site 30, indicate no unmitigable cultural sites in
the vicinity of the proposed facility.
Existing land use for Site 31 and 32 include coffee and tea production and an established
greenhouse. Site 30 is currently range land.
The current landowners of Site 30 are amenable to subdivision and sale.
Site 31 and 32 require uphill forcemain pumping transmission
The topography of Site 30 is less steep than Sites 31 and 32
Site 30 is closer to the collection area than site 31 and 32
8.8 Conclusion
Based on the analysis, Site 30 (TMK 9-5-007:016) was selected as the preferred location for the
Naalehu WWTP.
9-1
References
County of Hawaii. Letter to Community Homeowners, signed by Mayor Harry Kim. November 5, 2004.
Crites, Ron, and George Tchobanoglous. Small and Decentralized Wastewater Management Systems. WCB McGraw-
Hill, 1998.
Crites, Ronald W., E. Joe Middlebrooks, Robert K. Bastian, and Sherwood C. Reed. “Natural Wastewater Treatment Systems, Second Edition”. CRC Press, 2014.
Crites, Ronald W., E. Joe Middlebrooks, Sherwood C. Reed. Natural Wastewater Treatment Systems. CRC Taylor &
Francis, 2006.
Crites, Ronald W., Sherwood C. Reed, and Robert K. Bastian. “Land Treatment Systems for Municipal and Industrial Wastes”. McGraw-Hill, 2000.
Department of Planning, County of Hawaii. Kau Community Development Plan. October 2017.
Department of Public Works. Storm Drainage Standards, County of Hawaii, 1970.
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.
Fukunaga and Associates, Inc. Revised Preliminary Engineering Report – Naalehu Sewage Transmission,
Wastewater Treatment and Disposal System. June 2013.
Great Lakes – Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers.
Recommended Standards for Wastewater Facilities. 1997.
Hawaii Administrative Rules (HAR), Title 11, Department of Health Administrative Rules.
Masa Fujioka & Associates. Letter Report, Probing for Large Cavities (Lava Tubes), Naalehu and Naalehu Large
Capacity Cesspool Sewerage System. January 9, 2007.
M&E Pacific, Inc. Kau Sewer System Evaluation, Kau, Island of Hawaii, Hawaii. December 2004.
NRCS (National Resources Conservation Service). Web Soil Survey, located on the Internet at address
https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm . 2018.
Reed, Sherwood C., Ronald W. Crites, E. Joe Middlebrooks. Natural Systems for Waste Management and Treatment.
McGraw-Hill, Inc. 1995.
Rich, Linvil G. High Performance Aerated Lagoon Systems. American Academy of Environmental Engineers, 1999.
SSFM International, Inc. Final Preliminary Engineering Report for Naalehu and Naalehu 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.
Water Pollution Control Federation. Aeration, Manual of Practice FD-13. 1988.
White, George Clifford, Handbook of Chlorination and Alternative Disinfectants, John Wiley & Sons Inc., New York, 1999.
Naalehu Wastewater Treatment Plant Preliminary Engineering Report
A-1
Appendix A: Flow Projections Summary
Naalehu WWTP - Flow Projections SummaryNaalehu LCC Conversion ProjectBSFGWIADWF (BSF+GWI)PBSF (BSFx2.5)PDWF (PBSF+GWI)I/IDesign Flow (PDWF+I/I)Equivalent PopulationExisting Service Area 52,430 26,21578,645131,075 157,290 96,162253,452749Newly Accessible to Collection System91,620 54,180145,800229,050 283,230 152,593435,8231,548Grand Total 144,050 80,395224,445360,125 440,520 248,755689,2752,297Naalehu Full Buildout ConditionBSFGWIADWF (BSF+GWI)PBSF (BSFx2.5)PDWF (PBSF+GWI)I/IDesign Flow (PDWF+I/I)Equivalent PopulationExisting Service Area 52,430 26,21578,645131,075 157,290 96,162253,452749Newly Accessible to Collection System91,620 54,180145,800229,050 283,230 152,593435,8231,548Future Service Area (per Kau CDP)109,340 54,670164,010273,350 328,020 755,7331,083,7531,562Grand Total253,390 135,065388,455633,475 768,540 1,004,4881,773,0283,859NOTE: Design flow calculations based on City and County of Honolulu Wastewater System Design Standards, July 2017 (Chapter 2).Abbreviations:BSFBase Sanitary FlowPBSFPeak Base Sanitary FlowADWFAverage Dry Weather FlowGWIGroundwater Infiltration RatePDWFPeak Dry Weather FlowI/IWet Weather Infiltration / InflowDesign FlowPeak Hourly Flow
Naalehu Wastewater Treatment Plant Preliminary Engineering Report
B-1
Appendix B: Cost Estimates
Total($M)40.545.047.154.455.0County of Hawaii Department of Environmental ManagementNaalehu WWTPOptions Assessment Cost SummaryAnnual Recycled Water SalesEquipment Replacement at 20-YearsCapital CostsAnnual O&M Costs
Common Capital Inputs
Sep-18
Lagoon-Wetland Treatment
Total project cost:$18.2 million
Land Application
Total project cost:$8.0 million
County of Hawaii Department of Environmental Management
Naalehu WWTP
Preliminary Options Assessment - Capital Costs
Drainage Channel
Total project cost:$14.3 million
R-1 Treatment
Total project cost:$22.8 million
Limit of Treatment Technology
Total project cost:$30.6 million
Seasonal Storage Reservoir
Total project cost:$4.4 million
Diurnal R-1 Tank - Seasonal Program
Total project cost:
Diurnal R-1 Tank - Reservoir Program
Total project cost:
R-1 Delivery Pumps - Seasonal Program
Total project cost:
R-1 Delivery Pumps - Reservoir Storage
Total project cost:
R-1 Pipelines - Seasonal Program
Total project cost:
R-1 Pipelines - Reservoir Storage
Total project cost:
Common O&M Inputs
Lagoon Treatment/Wetlands/Disinfection
Labor
$41,600
Electricity
$131,579
Chemicals
$13,698
Maintenance
$91,080
Sludge Management
O&M Costs
County of Hawaii Department of Environmental Management
Naalehu WWTP
Preliminary Options Assessment
R-1 Treatment
Labor
$582,400
Electricity
$344,925
Chemicals
Maintenance
$113,757
Sludge Management
$49,275
Limit of Treatment Technology
Labor
$873,600
Electricity
$344,925
Chemicals
$41,095
Maintenance
$153,234
Sludge Management
$73,913
Seasonal Water Recycling (25%)
$5,637
Annual Water Recycling (100%)
$22,550
Avoided Cost of Pumping Irrigation Water
Recycled Water Pricing
Recycled Water Sales
Seasonal Recycling Sales
100% Recycling Sales
County of Hawaii Department of Environmental Management
Naalehu WWTP
R-1 Sales Assessment
County of Hawaii Department of Environmental Management
Naalehu WWTP
Preliminary Options Assessment
Operator Requirement Evaluation
Seasonal Recycling with DisposalRecycling efficiency:47%Recycling with Annual Storage ReservoirRecycling efficiency:104%County of Hawaii Department of Environmental ManagementNaalehu WWTPWater Recycling Assessments
County of Hawaii, DEMNaalehu WWTP Options AssessmentAlternatives Net Present Value AnalysisAgency: County of Hawaii, DEMSensitivity Adjustments (%)ResultsProject/Problem: Naalehu WWTP Options AssessmentRiskPremiumBenefitsCapital CostsOtherCostsCapital Cost30-yearNPVBenefit overStatus QuoAlternative 1Lagoons / wetlands/ disinfection / land application$40,500,000($50,317,478)Alternative 2R-1 treatment / land application$45,000,000($71,891,318) ($21,573,840)Alternative 3R-1 treatment / seasonal recycling (25%)$47,100,000($72,719,813) ($22,402,335)Alternative 4R-1 treatment / annual storage res (100%)$54,400,000($80,146,964) ($29,829,486)Alternative 5Limit of treatment technology / 25% recycle$55,000,000($91,059,595) ($40,742,117)Alternative 6Alternative 7Alternative 8Alternative 9Alternative 10Alternative 11Alternative 12Year of analysis: 2018Note: "Status quo" refers toEscalation rate: 3.20% Alternative 1Discount rate: 5.50%Make entries in yellow cells only