HomeMy WebLinkAboutPreliminary Engineering Report (Pahala WWTP) June 2018
Pahala Wastewater
Treatment Plant
Preliminary Engineering
Report
Prepared for
County of Hawaii, Department of
Environmental Management
June 2018
1955 Main Street, Suite 200
Wailuku, Hawaii 96793
Pahala Wastewater Treatment Plant
Preliminary Engineering Report
Prepared for
County of Hawaii, Department of Environmental Management
June 2018
THIS WORK WAS PREPARED BY ME OR UNDER MY SUPERVISION.
April 30, 2020
Signature Expiration Date of the License
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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 ..................................................................................................................... 1-1
2. Flow and Load Projections ............................................................................................................... 2-1
2.1 Service Area ........................................................................................................................... 2-1
2.2 Flow Projections ..................................................................................................................... 2-3
2.3 Influent Characteristics ......................................................................................................... 2-3
2.4 Influent Mass Loads .............................................................................................................. 2-3
2.5 Mass Loads to the Environment via Existing LCCs .............................................................. 2-4
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
Pahala 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 ................................. 4-11
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 ................................................................................................................. 4-20
4.6.1 Water ...................................................................................................................... 4-20
4.6.2 Access Road .......................................................................................................... 4-20
4.6.3 Stormwater Management ..................................................................................... 4-21
4.6.4 Pre-development Stormwater Conditions ............................................................ 4-21
4.6.5 Electrical Systems ................................................................................................. 4-25
4.6.6 Telemetry Systems ................................................................................................ 4-26
4.6.7 Operations Building ............................................................................................... 4-26
4.6.8 Site Fencing ........................................................................................................... 4-26
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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
v
7.2.4 Life-Cycle Costs ........................................................................................................ 7-8
7.3 Non-Economic Discussion ..................................................................................................... 7-9
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 ............................................................................................................................. 8-8
8.6 Weighted Analysis .................................................................................................................. 8-9
8.7 Results .................................................................................................................................. 8-10
8.8 Conclusion ............................................................................................................................ 8-10
9. References ....................................................................................................................................... 9-1
Appendix A: Cost Estimates ...................................................................................................................... A-1
Pahala Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
vi
List of Figures
Figure 1-1. Pahala Existing Sewer Collection System and LCC Service Area ...................................... 1-2
Figure 2-1. Pahala WWTP Service Area ................................................................................................. 2-2
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 .......................................................................... 4-7
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. Land Application System Schematic .............................................................................. 4-19
Figure 4-12. Existing Drainage System ................................................................................................ 4-22
Figure 4-13. Flood Insurance Rate Map .............................................................................................. 4-24
Figure 4-14. Operations Building Preliminary Floor Plan ................................................................... 4-27
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 Pahala 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
Figure 7-10. Life-Cycle Costs of Options ................................................................................................ 7-9
Figure 7-11. Comparison of Electrical Energy Requirements ............................................................ 7-11
Figure 8-1. Pahala Site Alternatives ...................................................................................................... 8-2
Pahala Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
vii
List of Tables
Table 2-1. Pahala WWTP Flow Projections ............................................................................................ 2-3
Table 2-2. Summary of Assumed Influent Characteristics ................................................................... 2-3
Table 2-3. Projected Influent Mass Loads ............................................................................................. 2-3
Table 2-4. Mass Loads to the Environment via Existing LCCs ............................................................. 2-4
Table 3-1. 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 ................................................................................................ 4-20
Table 5-1. Preliminary Design Criteria ................................................................................................... 5-4
Table 5-2. Environmental Benefits of Proposed Project ....................................................................... 5-7
Table 5-3. Pahala WWTP Order of Magnitude Construction Cost Estimate ........................................ 5-8
Table 5-4. Pahala 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
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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Table of Contents
viii
Table 8-5. Relative Weighting Factors ................................................................................................... 8-7
Table 8-6. Alternatives Analysis – Raw Scores ..................................................................................... 8-8
Table 8-7. Alternatives Analysis – Weighted Scoring ............................................................................ 8-9
Table 8-8. Alternative Site Ranking ..................................................................................................... 8-10
Pahala 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
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
scfm standard cubic feet
SCS Soil Conservation Service
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
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1-1
Introduction
1.1 Background
The town of Pahala is located in the Kau district of the Island of Hawaii. According to the 2010
United States Census, the town population is approximately 1,350 persons.
The Pahala 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. Many years after its establishment, the private sewer system
ownership was conveyed to the County of Hawaii (COH) Department of Environmental Management
(DEM).
In 1998, the U.S. Environmental Protection Agency (USEPA), promulgated regulations, 40 Code of
Federal Regulations (CFR) 144.14, that require the elimination of large capacity “gang” cesspools
(LCCs). The County intends to construct a new sewer collection system located within public right-of-
way (ROW) and replace the existing LCCs with a wastewater treatment plant to address the
wastewater treatment and disposal needs of the Pahala community.
This report summarizes a proposed wastewater treatment plant (WWTP) needed in order to treat and
dispose of the wastewater flow that is currently discharged to the LCCs, plus additional sewer
connections. The report presents the existing and estimated future flows and loads to the treatment
plant, the proposed treatment processes, recommendation for the WWTP upgrades needed to meet
the future treatment needs, and an initial opinion 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 collection
system is a network of gravity sewers that discharge to two 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 Pahala community existing sewer system consists of about 3,000 linear
feet of 6-inch diameter and 10,000 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 8 manholes in the sewer
system. There are no pump stations and the system is not designed to collect stormwater.
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. The report concludes with a site
selection consideration in Section 8.
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HUAPALA ST KOKIO STKEAHI STKAMANI ST
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TWOOD VALLEY RDMEYER RDPAAUAU STHAWAII BELT RDOHIA STILIAU STILIMA ST
LOW ER MAOULA RDHOLEI ST
PUMELI ST
SCALE AS SHOWN
JOB NO.: 150440
PAHALA WASTEWATER TREATMENT PLANT
Pahala Existing Sewer Collection System and LCC Service Area
FIGURE
1-1
0 2,0001,000
Feet
±
LEGEND
Existing Condition to Large Capacity Cesspool (LCC)
Proposed Pahala WWTP Site
P Pahala Existing SMH and LCC
")Existing Large Capacity Cesspool (LCC)
Existing Sewer Mains
Existing Large Capacity
Cesspool (LCC 1)
Existing Large Capacity
Cesspool (LCC 2)
Ka'u High &
Pahala ElementarySchool
Proposed PahalaWWTP Site
Ka'uHospital
2-1
Flow and Load Projections
This section summarizes the flow and load projections for the new WWTP.
2.1 Service Area
Within the town of Pahala, there is an existing wastewater collection that services approximately 109
properties. The collection system is currently located within easements in private properties and is
treated and disposed through two LCCs. Figure 2-1 shows the 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; however, the initial collection system and WWTP presented in this
report will service the properties currently connected to the LCCs or located adjacent 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 14.9-acre
site for the anticipated future expansion of the service area.
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")
")PUAHALA STPIKAKE STOHIA STKAMANI ST
PAAUAU PL
M
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S
T
HUAPALA STILIMA ST
PAK A LANA ST
PUMELI ST
HINANO ST KEAHI STKOALI STWOOD VALLEY RDMEYER RDKOKIO STHAWAII BELT RDPAAUAU STILIAU STLOWER MAOULA RDSCALE AS SHOWN
JOB NO.: 150440
PAHALA WASTEWATER TREATMENT PLANT
Pahala WWTP Service Area
FIGURE
2-1
0 2,0001,000
Feet
±
LEGEND
Existing Condition to Large Capacity Cesspool (LCC)
Initial Build Condition to WWTP Revised
Future Buildout Condition to WWTP (Ka'u CDP Service Area)
Proposed Pahala WWTP Site
Pahala Future County Sewer System
")Existing Large Capacity Cesspool (LCC)
Existing Large Capacity
Cesspool (LCC 1)
Existing Large Capacity
Cesspool (LCC 2)
Proposed PahalaWWTP Site
Ka'uHospital
Ka'u High &
Pahala ElementarySchool
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 2
2-3
2.2 Flow Projections
Wastewater flow projections were developed using the City and County of Honolulu’s (CCH) current
(2017) wastewater standards. Table 2-1 summarizes the flow projections.
Table 2-1. Pahala WWTP Flow Projections
Description Value Peaking Factor
Average dry weather flow 189,000 gallons per day 1.0
Peak day wet weather flow 662,000 gallons per day 3.5
Peak hour wet weather flow 630 gallons per minute 4.8
The WWTP will be designed to provide an average dry weather flow capacity of 190,000 gallons per
day.
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 190,000 gallons per day and the influent characteristics presented in Table 2-2.
Table 2-3. Projected Influent Mass Loads
Description Value
BOD5 480 lbs./day
TSS 480 lbs./day
Total nitrogen 60 lbs./day
Total phosphorus 10 lbs./day
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 2
2-4
2.5 Mass Loads to the Environment via Existing LCCs
Currently, 109 properties discharge without treatment to two LCCs, as shown in Figure 2-2. These
types of cesspools are a public health and environmental concern because of their likelihood of
releasing disease causing pathogens and other contaminants, such as nitrate, to groundwater. 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
Parameter Annual Load
BOD5 174,000 lbs./year
TSS 174,000 lbs./year
Total N 23,000 lbs./year
Total P 4,000 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
Effluent management options are evaluated below.
3.1.1 Ocean Discharge
Ocean discharge of treated effluent is not considered a viable option for this small community due to
the long distance to the shoreline (approximately 3 miles), high cost to construct an outfall, stringent
receiving water quality standards, high receiving water monitoring cost due to the distance to Hilo
harbor, and difficulty and length of time required to secure the required permits.
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. Since the town of Pahala is located mauka of the UIC line, an injection well is not a
viable option.
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 macadamia nut
trees. Figure 3-1 is a summary of the assessment that shows there is typically no irrigation demand
for six 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 is not a viable primary effluent management strategy for the community. However, water
recycling treatment, storage, and distribution systems could be added in the future.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 3
3-2
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 soils at the proposed WWTP location are suitable for slow rate (SR) land treatment. 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.
0
1
2
3
4
5
6
7
8
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECInches of WaterMonth
Precipitation Evapotranspiration Irrigation Requirement
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 3
3-3
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 indicate
approximately 20,000 linear feet of drain field trench would be required to accommodate the
anticipated flow. It would be difficult to evenly distribute effluent throughout a drain field of this size.
In addition, DOH regulations require a redundant drain field for subsurface disposal systems, making
this option expensive to implement. This option is considered impractical for the community.
3.1.6 Recommendation
A slow rate land treatment system is recommended for effluent management for the community.
3.2 Treatment Requirements
The DOH regulates land treatment as “land disposal” per Hawaii Administrative Rules (HAR) 11-62.
Table 3-1 lists the applicable effluent requirements for land disposal applicable to the project that
were in effect at the time this report was prepared.
Table 3-1. 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
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4-1
Wastewater Treatment Evaluations
This section presents the evaluations conducted in 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 Pahala
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.
Pahala 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'
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-4
4.1.5 Odor Control
A notorious 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 Pahala 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)
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-5
4.2 Aerated Lagoon Treatment System
The biological wastewater treatment needs at the Pahala 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 Pahala 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):
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-6
)20()025.1()(-
-=
Tw
S
Lsw
a
C
CC
NN
a
Where N = Equivalent oxygen transfer to tap water at standard conditions (lbs/hr)
aN = Oxygen required to treat the wastewater (lbs/hr)
a = (oxygen transfer in wastewater)/(oxygen transfer in tap water)
swC = PCss)(b = oxygen saturation value of the waste, mg/L
b = 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 g=
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)
airg = 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-7
outfitted with draft tubes to enhance deep water lagoon mixing or anti-erosion plates to ensure water
is drawn from the surface. Figure 4-4 shows a typical high-speed floating aerator.
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 Pahala 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 Pahala 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.
Figure 4-5. Normal Lagoon Configuration Schematic
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4-8
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 190,000 gallons per day.
Comparison of the minimum aerator requirements shown in Table 4-1 with the proposed aerator
layout shown in Figure 4-4 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 80,000 300 139 27 34
2 80,000 139 64 13 16
3 80,000 64 30 6 7
4 80,000 30 <30 2 3
4.2.4 Lagoon Liner
Lagoon liners are required 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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-9
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 balls 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-10
Figure 4-6. Floating HDPE Shade Balls
Figure 4-7. Floating shade balls with current and turbulence in reservoir.
Pahala 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 15 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 not offensive 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.
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
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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-12
• 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 Pahala
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. Calcium hypochlorite
decomposes in an exothermic reaction if exposed to moisture.
The solid can be directly applied to wastewater at very small WWTPs. Figure 4-9 shows a typical
calcium hypochlorite feed system.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-13
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 8 and 18 mg/L. The WWTP will discharge to a land application
system during normal flow and wet weather periods when the secondary effluent will be diluted by
precipitation falling onto the overland flow terraces. For planning purposes, a 10 mg/L dose was
assumed to be sufficient for the WWTP for most circumstances, but equipment will be sized to
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-14
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 lists the chlorine demand for various flow conditions.
Table 4-4. Chlorine Demand
Description Flow Chlorine Demand
Average dry weather flow 0.19 mgd 16 lbs./day
Peak day wet weather flow 0.662 mgd 55 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. For this application, the peak discharge rate will be equal to the peak day wet
weather flow, due to the flow equalization provided by the aerated lagoons. 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 460 gpm
Minimum chlorine contact tank 15 minutes
Tank volume required 920 cubic feet
Channel water depth 5 feet
Channel width 3 feet
Tank channel total length 61 feet
Tank dimensions including channel walls 13 feet x 24 feet
13'-0"24'-0"Path: P:\Projects\Hawaii, County Of (HI)\150440 COH Pahala WWTP\_CAD\0-PROJECT\FIGURESFile Name: 150440-FIG-ChlorContactTank Plot Date: March 22, 2018 4:32 PM Cadd User: Richard SellonaFIGURESCALE:
JOB NUMBER:
PAHALA WASTEWATER TREATMENT PLANT
CHLORINE CONTACT TANK
CONFIGURATION
4-10150440
Field
WASTEWATER
EFFLUENT
DISINFECTED
EFFLUENT
TO CHLORINATOR
BUILDING
CHLORINE
SOLUTION CHLORINE
CONTACT
CHANNEL
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-16
4.4.2 Ultraviolet Light (UV) Disinfection
A common alternative to a 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 nanometer.
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 a 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 630 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
Pahala 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 $200,000 $800,000
Annual Operations and Maintenance $15,000 $6,000
Life-cycle Cost (30-Year Net Present Value) $746,000 $947,000
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
avaliablity.
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 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-18
mechanisms. After an application period or wetting period, the surface can dry 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 system is
managed for that objective.
4.5.1 Design
The slow-rate system site consists of a net area of approximately 5.5 acres. The 5.5 acres will be
divided into 4 small groves of native trees, so that water application will be rotated to a different
grove each day. An additional small grove will be utilized as an emergency (overflow) or reserve
when surface or distribution system maintenance is conducted. By using one groove per day the
wet/dry cycle will be 1-day wetting and 3-days drying.
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 potential native tree 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 piping located on the surface. The piping will have 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 4-11 reflects
the proposed land application schematic.
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Path: P:\Projects\Hawaii, County Of (HI)\150440 COH Pahala WWTP\_CAD\0-PROJECT\FIGURESFile Name: 150440-FIG-LandAppSystem Plot Date: May 22, 2018 5:25 PM Cadd User: Richard SellonaFIGURE
JOB NO: 150440
PAHALA WASTEWATER TREATMENT PLANT
LAND APPLICATION SYSTEM SCHEMATIC 4-11
SCALE: 1" = 100'
SCALE IN FEET
0 100 200
50'
TYP
MAINTENANCE
ROAD, TYP
3:1 MAX, TYP 2:1 MAX, TYP
A A'
SECTION A - A'
GROVE 1
PLAN
GROVE 2 GROVE 3 GROVE 4
5'
GROVE 1 GROVE 2 GROVE 3
GROVE 4
EXISTING
GRADE = 8%±
H:V=3:1,
TYP
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
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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, it is recommended to construct approximately 2,000 linear feet of pipe
from the intersection of Huapala Street and Maile Street to the site and install a 1-inch water meter
with 1 ½-inch backflow preventer.
A plant water system will be supplied by the County water meter. 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 connections.
4.6.2 Access Road
All weather access will be required to operate and maintain the WWTP. Access to the site will be
provided by connection to Maile Street. A paved driveway apron is proposed at Maile Street and an
all-weather driveway will extend into the site and 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. For portions of the driveway that exceed 12 percent slope, a concrete pavement section is
recommended.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-21
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 to prevent increased flows and
volumes leaving the site on the 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.
4.6.4 Pre-development Stormwater Conditions
4.6.4.1 On-site
The majority of the proposed 42.5-acre site is currently utilized as macadamia nut orchards,
consisting of trees or unimproved agricultural roads. The parcel is bound on two sides by improved
county and state right-of-way and to the east by additional macadamia nut orchards.
The existing elevations range between 580 to 780 feet above mean sea level (MSL) and slopes in
the southerly direction at an average rate of 8 percent. The soils in this area are described as
Naalehu medial silty clay loam (NaC) by the Soils Conservation Service (SCS). These soils are
considered well drained with low runoff and slight erosion hazard.
On-site stormwater run-off generally sheet flows in a southerly direction to off-site swales along the
roadway frontages, Maile Street and Hawaiian Belt Road (also known as Mamalahoa Highway).
There is no known on-site drainage collection system, see Figure 4-12.
4.6.4.2 Off-site
Swales that run and collect along the roadway frontages of the property are conveyed through a box
culvert at the intersection of Maile Street and Hawaiian Belt Road and discharged makai. Similarly,
running along the north property line is an abandoned concrete flume, which was previously utilized
to discharge process water from the adjacent old sugar mill to agricultural land makai of Hawaiian
Belt Road. Figure 4-12 conceptualizes the existing drainage system.
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JOB NO: 150440 EXISTING DRAINAGE SYSTEM 4-12
SCALE: 1" = 200'
SCALE IN FEET
0 200 400HAWAII BELT ROADLOWER MAOULA ROADMAILE
S
T
R
E
E
T
TMK: (3) 9-6-002:021
TMK: (3) 9-6-005:054
TMK: (3) 9-6-002:049
TMK: (3) 9-6-002:016 TMK: (3) 9-6-002:044
(3) 9-6-002:024
PROPERTY
LINE, TYP
TMK: (3) 9-6-002:028
TMK: (3) 9-6-002:003
TMK: (3) 9-6-005:036
TMK: (3) 9-6-005:009
EXISTING
SHEET FLOW
TMK: (3)
9-6-005:051
NOTE:
TOPOGRAPHICAL CONTOURS ARE APPROXIMATE AND
BASED ON PAHALA USGS TOPO QUADRANGLE.
EXISTING
ROADWAY
GRASS SWALE
BISHOP ESTATES
(KAMEHAMEHA SCHOOLS)
TMK:(3) 9-6-002:018
42.5 ACRES
EXISTING
ROADWAY
CULVERT
EXISTING
ROADWAY
GRASS SWALE
STREAM
OLD SUGAR
MILL FLUME (MAMALAHOA HIGHWAY)
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-23
4.6.4.3 Flood Hazards
The subject property flood zone 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. 1551661800F. 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 4-13 for the Flood Insurance Rate Map.
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JOB NO: 150440 FLOOD INSURANCE RATE MAP 4-13
SCALE: 1"=2,000'
SUBJECT PROPERTY:
ZONE X - AREAS OF MINIMAL FLOODING
BISHOP ESTATES
(KAMEHAMEHA SCHOOLS)
TMK:(3)9-6-002:018
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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-25
4.6.4.4 Stormwater Quantity
The increase in peak flow and runoff volume is a function of the increase in impervious areas
associated with the proposed improvements.
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.
A drainage system will be designed to address stormwater surface run-off caused by impervious
portions of the WWTP development. Per the Hawaii County Code, Chapter 27, Section 20, the site
drainage plan shall accommodate the run-off caused by the proposed development, within the site
boundaries, for a one-hour, ten-year storm event. The pre-development runoff (10-year, 1-hour
storm) is approximately 23 cubic feet per second (cfs). The post-development runoff is
approximated at 24.5 cfs, which is a net increase of 1.5 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.
Furthermore, landscape buffers with dirt berms will be constructed around most of the perimeter of
the property acting as secondary containment in the event of a large storm event.
A complete analysis of the pre and post development drainage condition will be completed during
the design phase.
4.6.4.5 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.
To mitigate the quality of runoff, the drainage system will incorporate permanent Best Management
Practices (BMP’s). Recommended permanent BMP 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.
4.6.5 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 4
4-26
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.
4.6.6 Telemetry Systems
A land-line telephone telemetry system with auto-dialer will be provided to provide Hilo-based
operation staff of alarm conditions and key operational parameters at the WWTP. Additionally, a cell
phone will be available for backup.
4.6.7 Operations Building
An operations building will be constructed to include the electrical room, chlorinator room, restroom,
and maintenance/storage room, as shown in Figure 4-14.
4.6.8 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 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
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JOB NO: 150440 OPERATIONS BUILDING PRELIMINARY FLOOR PLAN 4-14
SCALE: 3/16" = 1'-0"
0 2'8'
SCALE: 3/16" = 1'-0"
4'12'1'3'
5-1
Preliminary Design of
Improvements
The following is a summary of the preliminary design for the proposed Pahala WWTP.
5.1 Site Plan
The existing parcel is an active macadamia nut tree orchard. The prevailing grade is in the north to
south direction at 5 to 10 percent slope. Approximately 14.9 acres of the 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.
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JOB NO: 150440 PRELIMINARY SITE PLAN 5-1
SCALE: 1" = 200'
HEADWORKS
SLOW RATE LAND
APPLICATION
GROVE, TYP
BISHOP ESTATES
(KAMEHAMEHA SCHOOLS)
TMK: (3) 9-6-002:018
42.5 ACRES
SCALE IN FEET
0 200 400 (MAMALAHOA HIGHWAY)LOWER MAOULA ROADMAILE
S
T
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PROPERTY
LINE, TYP
UNNAMED
DRAINAGE WAY
NOTE:
TOPOGRAPHICAL CONTOURS ARE APPROXIMATE
AND BASED ON PAHALA USGS TOPO QUADRANGLE.
OPERATIONS
BUILDING
DISINFECTION
1" WATER METER
FOR POTABLE
WATER
6" DOUBLE CHECK
DETECTOR ASSEMBLY
FOR FIRELINE
8" INFLUENT
SEWER FIRE
HYDRANT
LAGOON
1
LAGOON
3
LAGOON
4
LAGOON
2
FIRE HYDRANT
1,000' WELL
SETBACK
ODOR CONTROL
UNIT
LOT 2
(14.9 ACRES)
50' SETBACK
50' SETBACK
25' SETBACK
LOT 1
(27.6 ACRES)
W
E
T
L
A
N
D
GROVE 1
GROVE 2
25' WIDE UTILITY
EASEMENT (0.94 ACRES)
850'±
1500'±900'±830±FUTURE HEADWORKS
AND ODOR CONTROL
UNIT EXPANSION
EXISTING ACCESS VIA
KAMEHAMEHA SCHOOLS
FOR OTHERS TO REMAIN
(0.5 ACRES)
GROVE 3
GROVE 4
200'±DRIVEWAY
ACCESS
FOR WWTP HAWAII BELT ROAD
Path: P:\Projects\Hawaii, County Of (HI)\150440 COH Pahala WWTP\_CAD\0-PROJECT\FIGURESFile Name: 150440-FIG-LandAppPSys_Schem Plot Date: May 22, 2018 5:26 PM Cadd User: Richard SellonaFIGUREPAHALA WASTEWATER TREATMENT PLANT
JOB NO: 150440 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-4
5.3 Design Criteria
Table 5-1 provides preliminary design criteria.
Table 5-1. Preliminary Design Criteria
Description Value
Influent flows:
· Average dry weather 190,000 gpd
· Peak day wet weather 662,000 gpd
· Peak hour wet weather 630 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 6 feet
· Minimum carbon quantity 570 lbs
· Minimum bed depth 3 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 625 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
Pahala 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 630 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 15 feet
· Allowance for sludge 3 feet
· Total water depth 18 feet
· Side slope 3(H) : 1(V)
· Working volume of lagoon 1 to 3 0.80 Mgal
· Working volume of lagoon 4 1.60 Mgal
Aerators
· Type Floating mechanical surface aerators
· Cell 1 aerators 30 hp (2 at 15 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 0.25 acres
· Flow path length 50 feet
· Hydraulic application width 200 feet
· Media depth 24 inches
· Media type Medium gravel, D10 = ¾ inch
Pahala 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 10 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 to
minimize adverse impact to groundwater quality. The deep 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 deep percolate below the land treatment system 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 deep percolate from the land treatment system. Figure
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-7
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 174,000 lbs./year 600 lbs./year >99%
TSS 174,000 lbs./year 600 lbs./year >99%
Nitrogen 23,000 lbs./year 4,100 lbs./year 83%
Phosphorus 4,000 lbs./year 40 lbs./year >99%
Figure 5-3. Environmental Benefits of Proposed Project
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-8
5.5 Cost Estimates
An order of magnitude probable construction is summarized in Table 5-3. The estimate includes a
25 percent estimating contingency. The detailed cost estimate is included as Appendix A.
Table 5-3. Pahala WWTP Order of Magnitude Construction Cost Estimate
Description Estimated Construction Cost
Electrical and instrumentation $1,976,000
Headworks $906,000
Odor Control $412,000
Lagoons $2,222,000
Constructed Wetland $611,000
Land Application $925,000
On-site improvements $6,325,000
Off-site improvements $1,223,000
Total Estimated Construction Cost $14,600,000
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 2-1 shows the WWTP full
buildout service area.
Table 5-4. Pahala WWTP Full Buildout Flow Projections
Description Value Peaking Factor
Average dry weather flow 360,000 gallons per day 1.0
Peak day wet weather flow 1,260,000 gallons per day 3.5
Peak hour wet weather flow 1,200 gallons per minute 4.8
5.6.2 Improvements
To accommodate the flow increase anticipated from the full buildout of the Pahala wastewater
collection system, the WWTP will require facility upgrades. The recommended upgrades include
headworks and odor control expansion within the 14.9-acre 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 5
5-9
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
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.
Utilizing this lagoon system approach, the Pahala WWTP will require modifications at full buildout
flows, but is not anticipated to expand beyond the initial build 14.9 acres.
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 September 18, 2019
Complete construction of WWTP May 20, 2021
Connect existing collection system to WWTP June 30, 2021
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7-1
Alternative Treatment Options
Evaluation
Several other treatment alternatives were considered for the Pahala 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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-2
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 macadamia nut orchards. 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 Pahala 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 April through September, reaching a peak demand in June. The graph shows that no irrigation
is typically needed between October and March, because precipitation exceeds evaporation during
those months.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-3
Figure 7-4. Irrigation Demand Assessment
The potential demand for recycled water produced by the Pahala WWTP was assessed, as shown in
Figure 7-5. The WWTP could potentially provide irrigation water for approximately 62 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 62 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
The Pahala climate makes it possible to only recycle only about 25 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
0
1
2
3
4
5
6
7
8
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECInches of WaterMonth
Precipitation Evapotranspiration Irrigation Requirement
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMillion GallonsMonth
Recycled Water Use Effluent Disposal
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-4
throughout the year to be recycled. Figure 7-6 provides a comparison of the irrigation demand in
Pahala with the irrigation demand at Kealakehe.
Figure 7-6. Comparison of Irrigation Demands at Pahala 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.
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECUnit Irrigation Demand (gpd/acre)Month
Kealakehe (Parks and Golf Course)Pahala (Macadamia Nuts)
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-5
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 Pahala 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 Pahala 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 40 million gallons (Mgal) would occur during April, and by August the storage reservoir
would be dry and ready for another wet season. Under this scenario it would be possible to irrigate
approximately 253 acres of macadamia nut trees. The lined, 20-foot-deep storage reservoir would
have a water surface area of approximately 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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-6
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.
0
5
10
15
20
25
30
35
40
45
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMillion GallonsRecycled Water Supply Recycled Water Use Storage Volume
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-7
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 A. 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 $14.6 million
2 R-1 treatment/land application $18.4 million
3 R-1 treatment/seasonal water recycling $20.2 million
4 R-1 treatment and storage for 100% water recycling $30.4 million
5 Maximum practical treatment $26.0 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 $3.8 million.
Option 3 shows that addition of water recycling to reuse approximately 25 percent of the annual flow
would add an additional $1.8 million in capital costs. Option 4 shows that constructing a seasonal
storage reservoir to recycle 100 percent of the flow would add an additional $10 million in capital
costs. Comparison of options 3 and 5 shows that providing maximum practical treatment instead of
normal R-1 treatment would add $5.8 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-8
summary of the O&M cost estimates developed for the options. Additional details can be found in
Appendix A.
Table 7-2. Summary of O&M Cost Estimates
Option Name Estimated Annual O&M Cost
1 Aerated lagoons/constructed wetland/land application $236,000
2 R-1 treatment/land application $1,052,000
3 R-1 treatment/seasonal water recycling $1,055,000
4 R-1 treatment and storage for 100% water recycling $1,063,000
5 Maximum practical treatment $1,421,000
As shown in the table, 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 that 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 water it replaces.
The Pahala WWTP will be located at elevation 750 feet MSL. The cost to pump groundwater from
the basal lens to the ground surface at the WWTP is approximately $1,078 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 A.
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 17 $17,000
4 R-1 treatment and storage for 100% water recycling 70 $68,000
5 Maximum practical treatment 17 $17,000
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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-9
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 A.
Table 7-4. Summary of Life-Cycle Cost Estimates
Option Name Estimated Life-Cycle Cost
1 Aerated lagoons/constructed wetland/land application $21.2 million
2 R-1 treatment/land application $43.0 million
3 R-1 treatment/seasonal water recycling $44.5 million
4 R-1 treatment and storage for 100% water recycling $54.0 million
5 Maximum practical treatment $59.0 million
As shown in the table, option 1 incurs the lowest life-cycle costs, and the other options would all
incur over double to nearly triple the cost over the 30-year life-cycle. The life-cycle cost estimates are
shown graphically in Figure 7-10. The operating costs shown in the figure include benefits (i.e., cost
reductions) from recycled water sales where applicable.
Figure 7-10. Life-Cycle Costs of Options
As shown in the graph, the operating cost differential between option 1 and the other options is the
leading contributor to the lower life-cycle cost of option 1. The major operating cost differences are
discussed below.
7.3 Non-Economic Discussion
The options are discussed on a non-economic basis below.
0
10
20
30
40
50
60
1 2 3 4 530-Year Life-Cycle Cost ($ million)Option
Capital Costs Operating Costs
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-10
7.3.1 Labor Requirements
The Pahala 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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-11
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 15 to 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 Pahala. Therefore, the technology is considered to be not feasible.
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1 2 3 4 5Electricity Requirement (kWh/year)Option
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-12
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 190,000-
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 800,000-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 3,600 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 9-6-002:024 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:
· Closing LCC No. 2 that is located on private property would not be allowed, as it would
increase the flow to LCC No. 1 (converted to a seepage pit that is regulated as an injection
well) that is located on County property.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-13
· The capacity, structure, and condition of the existing LCC No. 1 is not known. The LCC could
either be a lava tube or a large conventional cesspool. A geotechnical investigation
conducted on the site to depths of 30 to 35 feet did not reveal the presence of lava tubes
(Masa Fujioka & Associates, January 9, 2007), therefore it is likely a large conventional
cesspool. The County attempted to determine the structure and condition of the LCC via
closed circuit TV inspection, but could not ascertain either due to technological limitations. It
is not known if the LCC could accommodate the flow from the existing service area if LCC No.
2 is closed.
· 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.
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 30 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 Puueo-Naalehu complex, 3 to
10 percent slopes in the National Resource Conservation Service soil survey. This soil type consists
of approximately 18 inches of extremely cobbly medial silt loam over cobbles and bedrock. This soil
profile is too thin for conventional soil absorption trenches, so residents with sufficient space 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 suitable subsurface geology could be located. However, previous subsurface investigations in
the community (Masa Fujioka & Associates, January 9, 2007, and Geolabs-Hawaii, September 23,
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 7
7-14
1998) revealed extremely permeable clinker layers and numerous lava tubes, both of which would
not meet HAR 11-62-34 requirements for seepage pits. For these reasons, conversion to individual
wastewater systems is considered to be not feasible.
8-1
Alternative Site Evaluation
Nine sites were evaluated as potential locations for the Pahala 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 Pahala WWTP were initially identified by the Department of
Environmental Management. Additional sites were identified based on feedback from the
Pahala community obtained during Community Outreach meetings that took place in
December 2017.
2. Four general categories and twenty-one criteria were established and defined for the
analysis.
3. Six “fatal flaw” conditions were identified. Sites with a 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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SCALE AS SHOWN
JOB NO.: 150440
PAHALA WASTEWATER TREATMENT PLANT
Pahala Site Alternatives
FIGURE
8-1
0 3,0001,500
Feet
±
LEGEND
Streams
!(Non-Potable Water Well
#*Potable Water Well
")Existing Large Capacity Cesspool (LCC)
Pahala WWTP Alternative Sites
ID No.Land Owner TMK1County of Hawaii 9-6-002:0242PMK Capital Partners LLC 9-6-002:0163Hawaii Electric 9-6-002:0434Mauna Loa Macadamia Orchards LP 9-6-002:0485State of Hawaii 9-6-002:0056State of Hawaii 9-6-002:0137Kamehameha Schools 9-6-002:0188Kamehameha Schools 9-6-002:0219Kamehameha Schools 9-6-002:049
Kauhuhu'ula
Gulch
Ka'ala'alaGulch
Keaiwa
Gulch
Pa'au'au
Gulch
Water Well #1 with
1,000ft Radius
Water Well #2 with
1,000ft Radius
Water Well #3 with
1,000ft Radius
Water Well #4 with
1,000ft Radius
1
2
3
4
5
6
9
8
7
PREVAILING WIND
N
W E
S
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-3
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 mitigatable
No information
available
Confirmed or
suspected sites
and mitigation
ability unknown
Confirmed sites
and mitigation
ability unknown
Confirmed sites
and
unmitigatable
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
unmitigatable
Visual impact Natural visual
mitigation (hill,
berm,
vegetation,
remoteness)
exists
Visible location,
mitigatable with
trees or other
engineered
buffers
Visible location,
unmitigatable
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.
Considerations specific to social impact include proximity to occupied buildings (including
residences, school, commercial establishments and others), prevailing wind direction, and visual
impact.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-4
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
Soils type Good soil and in
sufficient
amounts in area
of parcel useable
for disposal
Good soil but
over limited area
and disposal
modification
required
Marginal soil in
area of parcel
useable for
disposal
No soil in area of
parcel useable
for disposal
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
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
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
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-5
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
Commercial areas
become accessible
Additional
individual
residential
properties become
accessible outside
of LCC service area
No additional
properties become
accessible
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.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-6
Table 8-4 outlines the land use and availability 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. No fatal flaws were
identified for the land use and availability category.
Pahala 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 20% Distance from LCC collection area 50%
Gravity flow possible or pumping required 30%
Number of properties newly accessible 20%
100%
Land use and availability 10% Current ownership 55%
Current zoning and land use 45%
100%
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-8
8.5 Raw Scores
For the nine 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.
Table 8-6. Alternatives Analysis – Raw Scores
Category Criteria Site Raw Score
1 2 3 4 5 6 7 8 9
Environmental, social
and cultural
Presence of and/or proximity to archaeological/cultural sites 5 1 2 3 3 3 4 3 3
Proximity of treatment units to existing occupied buildings 3 3 5 5 5 5 5 5 5
Prevailing wind direction 5 5 5 5 5 5 5 5 5
Biology 3 3 3 3 3 3 3 3 3
Visual impact 3 3 3 5 5 5 3 3 3
Contamination from prior land use 3 1 3 1 3 3 3 3 3
Previously disturbed or developed 5 5 5 3 3 3 5 5 5
Location and site
characteristics
Parcel size a 0 5 0 5 5 5 5 5 5
Soils type 5 1 1 3 5 1 5 5 5
Topography 3 5 3 5 3 5 3 3 5
Proximity to water well b 0 5 5 3 5 5 5 5 5
Presence of lava tubes 1 1 3 3 3 3 3 3 3
Proximity to surface water, intermittent stream or coast line 5 5 5 5 3 5 5 1 5
Flood control / drainage 3 3 3 3 3 1 3 3 3
Existing vehicle access 5 5 2 2 2 5 5 5 2
Power and potable water availability 3 3 3 1 1 1 3 3 1
Collection system and
service area
Distance from LCC collection area 5 5 4 3 3 2 5 4 3
Gravity flow possible or pumping required 5 5 5 5 1 1 5 5 5
Number of properties newly accessible 3 3 3 3 3 3 3 3 3
Land use and availability
Current zoning and land use 3 3 3 3 3 3 3 3 3
Current ownership 5 5 3 3 5 5 4 4 4
Raw score totals (maximum possible = 105) FF 75 FF 72 72 72 85 79 79
a Fatal flaw condition for Sites 1 and 3.
b Fatal flaw condition for Site 1.
As indicated in Table 8-6, fatal flaw conditions were identified for Site 1 (due to both parcel size and
proximity to a drinking water well) and Site 3 (due to parcel size). These two sites were removed
from further analysis.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-9
8.6 Weighted Analysis
The weighted analysis is presented in Table 8-7.
Table 8-7. Alternatives Analysis – Weighted Scoring
Category Criteria Site Weighted Score
1 2 3 4 5 6 7 8 9
Environmental,
social and
cultural
Presence of and/or proximity to archaeological/cultural sites 0.25 0.75 0.75 0.75 1.00 0.75 0.75
Proximity of treatment units to existing occupied buildings 0.75 1.25 1.25 1.25 1.25 1.25 1.25
Prevailing wind direction 1.25 1.25 1.25 1.25 1.25 1.25 1.25
Biology 0.30 0.30 0.30 0.30 0.30 0.30 0.30
Visual impact 0.15 0.25 0.25 0.25 0.15 0.15 0.15
Contamination from prior land use 0.05 0.05 0.15 0.15 0.15 0.15 0.15
Previously disturbed or developed 0.25 0.15 0.15 0.15 0.25 0.25 0.25
Location and site
characteristics
Parcel size a 1.25 1.25 1.25 1.25 1.25 1.25 1.25
Soils type 0.25 0.75 1.25 0.25 1.25 1.25 1.25
Topography 0.75 0.75 0.45 0.75 0.45 0.45 0.75
Proximity to water well b 0.50 0.30 0.50 0.50 0.50 0.50 0.50
Presence of lava tubes 0.08 0.24 0.24 0.24 0.24 0.24 0.24
Proximity to surface water, intermittent stream or coast line 0.30 0.30 0.18 0.30 0.30 0.18 0.30
Flood control / drainage 0.15 0.15 0.15 0.05 0.15 0.15 0.15
Existing vehicle access 0.15 0.06 0.06 0.15 0.15 0.15 0.06
Power and potable water availability 0.09 0.03 0.03 0.03 0.09 0.09 0.03
Collection
system and
service area
Distance from LCC collection area 2.50 1.50 1.50 1.00 2.50 2.00 1.50
Gravity flow possible or pumping required 1.50 1.50 0.30 0.30 1.50 1.50 1.50
Number of properties newly accessible 0.60 0.60 0.60 0.60 0.60 0.60 0.60
Land use and
availability
Current zoning and land use 1.35 1.35 1.35 1.35 1.35 1.35 1.35
Current ownership 2.75 1.65 2.75 2.75 2.20 2.20 2.20
Overall weighted totals (maximum possible = 5) FF 3.61 FF 3.76 3.76 3.46 4.33 4.06 4.10
a Fatal flaw condition for Sites 1 and 3.
b Fatal flaw condition for Site 1.
Pahala Wastewater Treatment Plant Preliminary Engineering Report Section 8
8-10
8.7 Results
The results of the analysis are presented in Table 8-8. Two sites were identified as having fatal flaws
and the remaining seven were ranked in accordance with the overall weighted score.
Table 8-8. Alternative Site Ranking
Rank Site
1 7
2 9
3 8
4 5
5 4
6 2
7 6
FF 1
FF 3
The top three sites for the Pahala WWTP are:
1. Site 7 (TMK 9-6-002:18)
2. Site 9 (TMK 9-6-002:49)
3. Site 8 (TMK 9-6-002:21)
Site 7 is preferred to the second and third ranked sites for the following reasons:
· A preliminary Archaeological Inventory Survey has been performed for Site 7, indicating no
unmitigable cultural sites on the property.
· Site 8 is bisected by an intermittent stream bed, and a steep gulch borders the property to
the west.
· Site 7 is closer to the existing collection area than both Site 8 and Site 9.
· Power and potable water are more readily available to Site 7. Site 9 will require the utilities
to cross the highway.
8.8 Conclusion
Based on the analysis, Site 7 (TMK 9-6-002:18) was selected as the preferred location for the
Pahala WWTP.
9-1
References
CH2MHILL. Kau High School and Pahala Elementary School Connection to County Sewer. July 2017.
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 Wastewater Management, City and County of Honolulu, State of Hawaii. Design Standards of the
Department of Wastewater Management, Volume 1 and 2. July 2017.
Great Lakes – Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers.
Recommended Standards for Wastewater Facilities. 1997.
Hawaii Administrative Rules (HAR), Title 11, Department of Health Administrative Rules.
Masa Fujioka & Associates. Letter Report, Probing for Large Cavities (Lava Tubes), Naalehu and Pahala Large
Capacity Cesspool Sewerage System. January 9, 2007.
M&E Pacific, Inc. Kau Sewer System Evaluation, Kau, Island of Hawaii, Hawaii. December 2004.
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 Pahala Large Capacity Cesspool
Conversion Projects, July 2007.
USEPA. “Process Design Manual, Land Treatment of Municipal Wastewater Effluents”. EPA/625/R-06/016.
September 2006.
Water Environment Federation. Wastewater Disinfection, Manual of Practice FD-10. Water Environment Federation,
1996.
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.
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Pahala Wastewater Treatment Plant Preliminary Engineering Report
A-1
Appendix A: Cost Estimates
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County of Hawaii Department of Environmental Management
Pahala WWTP
Preliminary Design - Order of Magnitude Construction Cost
Electrical and instrumentation 1,976,000$
Headworks 906,000$
Odor Control 412,000$
Lagoons 2,222,000$
Wetland 611,000$
Land Application 925,000$
On-site improvements 6,325,000$
Off-site improvements 1,223,000$
Total Estimated Construction Cost 14,600,000$
Description Quantity Units Unit Cost Extension
Clear and grub 18.0 AC $5,995 $107,910
BMP's 18.0 AC $13,080 $235,440
Archaeological Monitoring 18 AC $2,507 $45,126
Earthwork 52,000 CY $25 $1,300,000
Sewerline extension 700 LF $218 $152,600
Operations building 1,500 SF $500 $750,000
Generator and tank 1 LS $250,000 $250,000
Fencing 3,200 LF $164 $523,200
Paving 38,000 SY $55 $2,071,000
Off-site waterline 2,500 LF $327 $817,500
On-site waterline 900 LF $164 $147,150
On-site fireline 750 LF $218 $163,500
Off-site overhead electrical 1 LS $50,000 $50,000
Trees (landscaping & Irrigation)10 EA $2,500 $25,000
Headworks 1 EA $501,339 $501,339
Odor control unit 1 EA $329,797 $329,797
Lagoons 1 LS $1,816,902 $1,816,902
Constructed Wetland 1 LS $489,000 $489,000
Chlorine contact tank 1 LS $150,000 $150,000
Chlorine feed system 1 LS $26,577 $26,577
Land Application piping 2,700 LF $125 $337,500
Land Application trees/ground cover 5.5 AC $5,000 $27,500
Effluent flow meter and sampler 1 LS $154,780 $154,780
$10,472,000
15%$1,570,800
1.0%$104,720
$12,148,000
20%$2,430,000
$14,600,000.00TOTAL ORDER OF MAGNITUDE CONSTRUCTION COST
Subtotal
On-site electrical
Mobilization/Demoblization
Total
Contingency
A-2
A-3
OptionTotalNo.TreatmentDisposalRecyclingLagoonsR-1Limit of TTDisposalReservoirDiurnal TankR-1 PumpsR-1 Pipelines($M)1Aerated lagoons/wetland/disinfectionLand applicationNone10.83.814.62MBR (R-1)Land applicationNone14.63.818.43MBR (R-1)Land applicationSeasonal (25% of total annual flow)14.63.80.80.50.520.24MBR (R-1)Land applicationAnnual storage reservoir (100% of flow)14.63.86.13.51.01.530.45Limit of treatment technologyLand applicationSeasonal (25% of total annual flow)20.43.80.80.50.526.0No.TreatmentDisposalRecyclingLaborElectricityChemicalsMaintenanceSludge MgmtTotal1Aerated lagoons/wetland/disinfectionLand applicationNone$42,000$118,000$12,000$54,000$10,000$236,0002MBR (R-1)Land applicationNone$582,000$345,000$10,000$73,000$42,000$1,052,0003MBR (R-1)Land applicationSeasonal (25% of total annual flow)$582,000$348,000$10,000$73,000$42,000$1,055,0004MBR (R-1)Land applicationAnnual storage reservoir (100% of flow)$582,000$356,000$10,000$73,000$42,000$1,063,0005Limit of treatment technologyLand applicationSeasonal (25% of total annual flow)$874,000$348,000$35,000$102,000$62,000$1,421,000No.TreatmentDisposalRecyclingHigh PriceLow Price1Aerated lagoons/wetland/disinfectionLand applicationNone$0$02MBR (R-1)Land applicationNone$0$03MBR (R-1)Land applicationSeasonal (25% of total annual flow)$17,000$9,0004MBR (R-1)Land applicationAnnual storage reservoir (100% of flow)$68,000$38,0005Limit of treatment technologyLand applicationSeasonal (25% of total annual flow)$17,000$9,000EquipmentNo.TreatmentDisposalRecyclingReplacement1Aerated lagoons/wetland/disinfectionLand applicationNone$2,693,0002MBR (R-1)Land applicationNone$3,653,0003MBR (R-1)Land applicationSeasonal (25% of total annual flow)$3,653,0004MBR (R-1)Land applicationAnnual storage reservoir (100% of flow)$3,653,0005Limit of treatment technologyLand applicationSeasonal (25% of total annual flow)$5,097,000Annual Recycled Water SalesEquipment Replacement at 20-YearsAnnual R-1 Water SalesCapital Cost ($M)County of Hawaii Department of Environmental ManagementPahala WWTPOptions Assessment Cost SummaryAnnual O&M Costs ($)Capital CostsAnnual O&M CostsA-4
Common Capital Inputs
Current ENRCCI:10870
Area markup factor:30%
Contingency factor:20%
Project soft costs factor:25%
Lagoon-Wetland Treatment
Description Quantity Units Unit Cost Extension
Clear and grub 8 AC $15,000 $120,000
BMPs 8 AC $13,000 $104,000
Earthwork 9,500 CY $25 $237,500
Sewer extension 700 LF $160 $112,000
Headworks 1 EA $500,000 $500,000
Lagoons 1 LS $1,800,000 $1,800,000
Wetlands 1 LS $350,000 $350,000
Chlorine contact tank 1 LS $100,000 $100,000
Chlorine feed system 1 LS $30,000 $30,000
Operations building 1,500 SF $500 $750,000
Generator and tank 1 LS $250,000 $250,000
Fencing 1,500 LF $100 $150,000
Paving 15,000 SY $55 $825,000
Water line extension 1,500 LF $160 $240,000
Yard piping 1 LS $200,000 $200,000
Miscellaneous site work 1 LS 100,000 $100,000
HELCO power 1 LS 50,000 $50,000
Hawaiian Telcom 1 LS 20,000 $20,000
Archeological monitoring 8 AC 2,500 $20,000
Visual buffer trees and irrigation 10 EA 2,500 $25,000
Subtotal $5,983,500
Electrical and instrumentation 20%$1,196,700
Total construction $7,180,200
Contingency $1,436,040
Total construction $8,616,240
Project soft costs $2,154,060
Total project cost:$10.770 million
Land Application
Description Quantity Units Unit Cost Extension
Clear and grub 6 AC $15,000 $82,500
BMPs 6 AC $13,000 $71,500
Earthwork 33,500 CY $25 $837,500
Fencing 1,700 LF $100 $170,000
Paving 23,000 SY $30 $690,000
Yard piping 3,500 LF $160 $560,000
Planting 6 AC 10,000 $60,000
Effluent flow meter and sampler 1 LS 50,000 $50,000
Archeological monitoring 6 AC 2,500 $15,000
Subtotal $2,536,500
Electrical and instrumentation 0%$0
Total construction $2,536,500
Contingency $507,300
Total construction $3,043,800
Project soft costs $760,950
Total project cost:$3.805 million
County of Hawaii Department of Environmental Management
Pahala WWTP
Preliminary Options Assessment - Capital Costs
A-5
R-1 Treatment
Capacity:0.19 mgd
Mainland cost at current ENRCCI:$39.44 /gpd from R-1 WWRF capital regression. y=24.003*(x^-0.299)
Local construction cost:$51.27 /gpd
Construction estimate:$9.7 million
Contingency:$1.9 million
Total construction cost:$11.7 million
Project soft costs:$2.9 million
Total project cost:$14.6 million
Limit of Treatment Technology
ENRCCI of estimate:8952
10 mgd WWTP cost:$13.80 /gpd
10 mgd WWTP cost at current ENRCCI:$16.76 /gpd
Local 10 mgd WWTP cost:$21.78 /gpd
Small flow escalation:$71.54 /gpd y=43.47x^-0.3 Per WERF analysis. BNR + advanced nutrient removal
Construction estimate:$13.6 million
Contingency:$2.7 million
Total construction cost:$16.3 million
Project soft costs:$4.1 million
Total project cost:$20.4 million
Seasonal Storage Reservoir
Volume:124 ac-ft
Mainland construction cost:$25,000 /ac-ft
Subtotal:$3.1 million
Local construction cost:$4.0 million
Contingency:$0.8 million
Total construction cost:$4.8 million
Project soft costs:$1.2 million
Total project cost:$6.1 million
Diurnal R-1 Tank - Seasonal Program
Volume:0.19 mgal 1 peak day
Local construction cost:$3.00 /gallon
Subtotal:$0.6 million
Contingency:$0.1 million
Total construction cost:$0.7 million
Project soft costs:$0.1 million
Total project cost:$0.8 million
Diurnal R-1 Tank - Reservoir Program
Volume:0.77 mgal 1 peak day
Local construction cost:$3.00 /gallon
Subtotal:$2.3 million
Contingency:$0.5 million
Total construction cost:$2.8 million
Project soft costs:$0.69 million
Total project cost:$3.5 million
A-6
R-1 Delivery Pumps - Seasonal Program
Peak day flow 0.19 mgal
Delivery time:8 hours
Pumping capacity:396 gpm
Mainland construction cost @ ENRCCI 4500:$100,000
Current mainland construction cost:$242,000
Local construction cost:$315,000
Contingency:$63,000
Total construction cost:$378,000
Project soft costs:$94,500
Total project cost:$0.5 million
R-1 Delivery Pumps - Reservoir Storage
Peak day flow 0.77 mgal
Delivery time:8 hours
Pumping capacity:1604 gpm
Mainland construction cost @ ENRCCI 4500:$200,000
Current mainland construction cost:$483,000
Local construction cost:$628,000
Contingency:$125,600
Total construction cost:$753,600
Project soft costs:$188,400
Total project cost:$1.0 million
R-1 Pipelines - Seasonal Program
Peak delivery rate:396 gpm
Pipeline diameter:6 inches
Hawaii construction cost:$25 /in-ft
Estimated length:2000 feet
Local construction cost:$300,000
Contingency:$60,000
Total construction cost:$360,000
Project soft costs:$90,000
Total project cost:$0.5 million
R-1 Pipelines - Reservoir Storage
Peak delivery rate:1604 gpm
Pipeline diameter:10 inches
Hawaii construction cost:$25 /in-ft
Estimated length:4000 feet
Local construction cost:$1,000,000
Contingency:$200,000
Total construction cost:$1,200,000
Project soft costs:$300,000
Total project cost:$1.5 million
A-7
Common O&M Inputs
Labor cost:$100 /hr (loaded)
FTE effective labor:1,560 hours/year
Chlorine tab cost:$4 /lb
Alum cost:$2 /lb
Electricity cost:$0.35 /kWh
Maintenance cost:2%/year of equipment capital
Sludge management cost:$1,500 /dry ton, dewatering, hauling, tip fee
Average flow:0.19 mgd
Lagoon Treatment/Wetlands/Disinfection
Labor
Normal requirement:1 visit/week
Operators/visit:1
Time per visit:8 hours/visit
Weekly labor hours:8 hours/week
Annual labor hours:416 hours/year
FTEs:0.3 FTEs
Annual labor cost:$41,600 /yr
Electricity
Load Equiv hp Percent kWhr/mo $/month
Aerators 50 100%26,845 $9,396
Screens 2 10%107 $38
Chlorine pumps 0.5 30%81 $28
Effluent pumps 2 100%1,074 $376
Totals $9,837
Annual power cost:$118,049
Annual power consumption:337283 kWh/yr
Chemicals
Chlorine dose:5 mg/L
Daily use:8 lbs/d
Annual use:2892 lbs/d
Annual cost:$11,568 /yr
Maintenance
Equipment cost:$2,692,575 (assume 25% of capital cost)
Annual maintenance:$53,852 /yr
Sludge Management
Production rate:0.1 dry tons/mgal
Annual production:6.935 /dry tons
Sludge management cost:$10,403 /year (deferred for 20 years)
R-1 Treatment
Labor
Normal requirement:7 visits/week
Operators/visit:2
Time per visit:8 hours/visit
Weekly labor hours:112 hours/week
Annual labor hours:5824 hours/year
FTEs:3.7 FTEs
Annual labor cost:$582,400
O&M Costs
County of Hawaii Department of Environmental Management
Pahala WWTP
Preliminary Options Assessment
A-8
Electricity
Daily power use:2,700 kWh/d
Annual power use:985,500 kWh/yr
Annual power cost:$344,925 /yr
Chemicals
Annual chemical cost:$10,000
Maintenance
Equipment cost:$3,652,973 (assume 25% of capital cost)
Annual maintenance:$73,059 /yr
Sludge Management
Sludge production:0.4 dry tons/mgal
Annual production:28 /dry tons
Sludge management cost:$41,610 /year
Limit of Treatment Technology
Labor
Normal requirement:7 visits/week
Operators/visit:3
Time per visit:8 hours/visit
Weekly labor hours:168 hours/week
Annual labor hours:8736 hours/year
FTEs:5.6 FTEs
Annual labor cost:$873,600
Electricity
Daily power use:2,700 kWh/d
Annual power use:985,500 kWh/yr
Annual power cost:$344,925 /yr
Chemicals
Alum dose 30 mg/L
Alum use:48 lbs/d
Alum cost:$34,703 /yr
Maintenance
Equipment cost:$5,097,397 (assume 25% of capital cost)
Annual maintenance:$101,948 /yr
Sludge Management
Sludge production:0.6 dry tons/mgal
Annual production:42 /dry tons
Sludge management cost:$62,415 /year
Seasonal Water Recycling (25%)
Load Equiv hp Percent kWhr/mo $/month
R-1 delivery pumps 5 25%671 $235
Totals $235
Annual power cost:$2,819
Annual power consumption:8054 kWh/yr
Annual Water Recycling (100%)
Load Equiv hp Percent kWhr/mo $/month
R-1 delivery pumps 5 100%2,685 $940
Totals $940
Annual power cost:$11,275
Annual power consumption:32214 kWh/yr
A-9
Avoided Cost of Pumping Irrigation Water
Assume pumping from basal lens
Elevation at WWTP:750 feet MSL
Flow rate:1000 gpm
2.2 cfs
Pump efficiency:85%
Motor efficiency:90%
Power cost:$0.35 /kWh
BHP:223 hp
Motor draw:185 kW
Unit volume:1 mgal
Time to pump unit vol:16.7 hours
Power to pump unit vol:3080 kWh
Cost to pump unit vol:$1,078
Recycled Water Pricing
High price:90%of avoided cost
Low price:50%of avoided cost
Recycled Water Sales
High price:$970 /mgal
Low price:$539 /mgal
Seasonal Recycling Sales
Annual reuse volume:17 mgal
High price sales:$16,661 /year
Low price sales:$9,256 /year
100% Recycling Sales
Annual reuse volume:70 mgal
High price sales:$67,987 /year
Low price sales:$37,770 /year
County of Hawaii Department of Environmental Management
Pahala WWTP
R-1 Sales Assessment
A-10
County of Hawaii, DEMPahala WWTP Options AssessmentAlternatives Net Present Value AnalysisAgency: County of Hawaii, DEMSensitivity Adjustments (%)ResultsProject/Problem: Pahala WWTP Options AssessmentRiskPremiumBenefitsCapital CostsOtherCostsCapital Cost30-yearNPVBenefit overStatus QuoAlternative1Lagoons / wetlands/ disinfection / land application$14,600,000($21,196,947)Alternative2R-1 treatment / land application$18,400,000($42,993,152) ($21,796,205)Alternative3R-1 treatment / seasonal recycling (25%)$20,200,000($44,496,467) ($23,299,520)Alternative4R-1 treatment / annual storage res (100%)$30,400,000($53,785,222) ($32,588,276)Alternative5Limit of treatment technology / 25% recycle$26,000,000($58,961,593) ($37,764,647)Alternative6Alternative7Alternative8Alternative9Alternative10Alternative11Alternative12Year of analysis: 2017Note: "Status quo" refers toEscalation rate: 3.20% Alternative 1Discount rate: 5.50%Make entries in yellow cells onlyAll entries in dollarsAll entries in thousands of dollarsSelect one A-11
No.Treatment Disposal Recycling
1 Aerated lagoons/disinfection Land application None
2 MBR (R-1)Land application None
3 MBR (R-1)Land application Seasonal (25% of total annual flow)
4 MBR (R-1)Land application Annual storage reservoir (100% of flow)
5 Limit of treatment technology Land application Seasonal (25% of total annual flow)
Criteria per HAR 11-61 1 2 3 4 5
Population served 1 1 1 1 1
Design average flow 1 1 1 1 1
Effluent discharge 2 2 6 6 6
Variation on raw wastes 0 0 0 0 0
Pretreatment 5 10 10 10 10
Primary treatment 0 0 0 0 0
Secondary treatment 8 15 15 15 20
Advanced waste treatment 0 12 12 12 22
Additional treatment processes 7 7 7 7 7
Solids handling 0 19 19 19 19
Disinfection 5 10 10 10 10
Laboratory control bacteriological 0 0 0 0 0
Laboratory control chemical/physical 0 0 0 0 0
Total points 29 77 81 81 96
WWTP Classification per 11-61 I IV IV IV IV
Option
County of Hawaii Department of Environmental Management
Pahala WWTP
Preliminary Options Assessment
Operator Requirement Evaluation
A-12
Seasonal Recycling with DisposalAverage flow:0.19mgdIrrigated acreage:62acresWW FlowDisposalMonthDays(mgal)(gpd/ac)(mgal)(mgal)Jan315.900.05.9Feb285.300.05.3Mar315.900.05.9Apr305.76441.24.5May315.92,2444.31.6Jun305.73,0435.70.0Jul315.91,3482.63.3Aug315.91,4522.83.1Sep305.73340.65.1Oct315.900.05.9Nov305.700.05.7Dec315.900.05.9Totals36569.351752Recycling efficiency:25%Recycling with Annual Storage ReservoirAverage flow:0.19mgdIrrigated acreage:253acresReservoir surface area:6.4acresReservoir pan coefficient:0.7Reservoir StorageWW FlowWW inPan EvapDelta StorageWater DepthMonthDays(mgal)(gpd/ac)(mgal)(mgal)(inches)(mgal)(inches)Inches(mgal)(mgal)(mgal)(ac-ft)(feet)Jan315.900.05.95.981.04.553.20.66.428.186.313.5Feb285.300.05.33.770.74.543.20.65.433.5102.916.1Mar315.900.05.95.450.94.973.50.66.239.8122.019.1Apr305.76444.90.83.230.65.43.80.70.740.5124.219.4May315.9224417.6-11.71.940.35.63.90.7-12.128.487.313.6Jun305.7304323.1-17.41.560.35.944.20.7-17.810.632.55.1Jul315.9134810.6-4.73.270.66.374.50.8-4.95.717.52.7Aug315.9145211.4-5.53.080.56.234.40.8-5.70.00.00.0Sep305.73342.53.23.60.65.553.90.73.13.19.61.5Oct315.900.05.93.980.75.053.50.66.09.127.94.4Nov305.700.05.76.71.24.493.10.56.315.447.37.4Dec315.900.05.95.821.04.623.20.66.321.766.710.4Totals36569.357048.48.463.37.70.0Recycling efficiency:101%Max Volume:40Mgal124ac ftPeak demand:23.1mgal/mo0.77mgdCounty of Hawaii Department of Environmental ManagementPahala WWTPWater Recycling AssessmentsIrrig DemandIrrig Demand Precipitation in Evap out Cumulative Storage
A-13