HomeMy WebLinkAboutAgenda Item IV.2.b_2026-06 Ali'i Drive Sewer Line Extension Preliminary Engineering ReportPRELIMINARY ENGINEERING REPORT
ALIʻI DRIVE SEWER LINE EXTENSION
Kailua-Kona, Hawai‘i
Tax Map Keys: (3) 7-7-010, (3) 7-8-014
June 2026
Prepared for:
County of Hawaii
Department of Environmental
Management, Wastewater Division
345 Kekuanaoa Street, Suite 41
Hilo, Hawaii 96720
Prepared by:
Bowers + Kubota Consulting, Inc.
2153 North King Street, Suite 200
Honolulu, Hawai‘i 96819
24A0108.00
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1 GENERAL INFORMATION
This preliminary engineering report (PER) supports a proposed project to construct wastewater
system improvements along the coast near Kahalu‘u Bay, located on the west side of Hawaiʻi Island
as shown in Figure 1. The County of Hawaiʻi (COH) supports this project in response to scientific
studies identifying cesspool leachate as a source of contamination in Kahaluʻu Bay. The project
seeks to implement a sanitary sewer solution that will significantly improve water quality at this
natural attraction, where many come to surf, snorkel, swim, and enjoy the bay.
2 PROJECT DESCRIPTION
2.1 LOCATION
The project is in the North Kona District, island of Hawaiʻi, within the coastal ahupuaʻa of Kahaluʻu.
The project extends along approximately 3,400 linear feet of Aliʻi Drive, between Queen Kalama
Avenue to the north and Mokolea Street to the south. The project area includes 77 parcels fronting
Aliʻi Drive, consisting of a mix of single family residential, multi-family residential, and resort-zoned
properties. These parcels are currently served by individual cesspools or on-site wastewater
systems and do not have access to a public sanitary sewer system.
Existing County of Hawaiʻi sewer infrastructure to the north terminates near Queen Kalama
Avenue, while sewer service to the south is provided by a privately owned system operated by
Hawaiʻi Water Service (HWS) in the Keauhou Resort area, which terminates near Makolea Street.
The project area gently slopes from north to south towards Makolea Street. Based on topographic
survey, ground elevations of the site range from about 23 to 11 feet mean sea level.
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Figure 1 - Location Map
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2.2 LAND USE AND ZONING
The State and County land use designations for the parcels surrounding the Project Area reflect a
mix with some Single-Family Residential (RS-7.5), Multiple-Family Residential District (RM-3.5),
and Resort-Hotel District (V-1.25) as shown in Figure 2. These land use designations were used to
estimate population, wastewater generation, and design flows in Section 2.5.
Figure 2 - State and County Land Use Designation
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2.3 ENVIRONMENTAL RESOURCES
The project area is located within a portion of the Kāpalaʻalaea 2nd and Kahaluʻu ahupuaʻa that has
been extensively documented as archaeologically sensitive based on prior investigations and the
Archaeological Literature Review and Field Inspection (LRFI) completed for the project. Historic
properties previously identified within and adjacent to the Aliʻi Drive corridor re?lect sustained use
of the area from the precontact period through the historic era. The project area lies within the kula
zone of the Kona Field System and partially within the Kahaluʻu Historic District, both of which
represent regionally significant cultural landscapes associated with traditional Hawaiian
agricultural practices, settlement patterns, transportation networks, and ceremonial activity, see
Figure 3.
Documented archaeological resources within the vicinity of the project include heiau, residential
sites, agricultural features, boundary walls, mauka–makai trails, segments of the King’s Highway,
and lava tubes known or suspected to contain human burials. Collectively, these resources
represent a range of functional site types associated with religious practices, habitation,
subsistence agriculture, land tenure, and transportation. Historical records and earlier surveys
further indicate that additional cultural features—some no longer extant due to roadway
construction and mid-20th-century development—were formerly present along the Aliʻi Drive
alignment, particularly in coastal and nearshore areas of Kahaluʻu. The density and diversity of
known resources are consistent with Kahaluʻu’s established role as a major population and
ceremonial center in North Kona.
Although the existing Aliʻi Drive roadway prism has been subject to repeated disturbance
associated with road improvements and utility installation over the past century, the LRFI
concludes that intact archaeological deposits may remain in adjacent parcels and in subsurface
contexts outside of previously disturbed areas. Archaeological sensitivity remains elevated in
locations where work may extend beyond the existing roadway alignment, where historic boundary
walls or landforms are present, or where lava tubes occur beneath or adjacent to the corridor. As a
result, archaeological and cultural resources represent a project constraint that will require
consideration during subsequent phases of design and environmental review, including avoidance
where practicable and coordination with the State Historic Preservation Division to address
compliance requirements. The coastal setting of the project area introduces additional
considerations related to flooding and sea level rise that may affect both project design and
long-term resource protection, as discussed in Section 2.4.
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Figure 3 - Archaeological Site Map (extracted from Archaeological Literature Review and Field Inspection for the Aliʻi Drive
Sewer Line Extension Project by ASM Affiliates, Inc.)
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2.4 COASTAL FLOODING AND SEA-LEVEL RISE
CONSIDERATIONS
There are no mapped wetlands or perennial streams within the Project Area. A portion of the
southern end of the corridor lies within the FEMA 100-year VE coastal flood zone due to its
proximity to the shoreline, see Figure 4. This condition is an important consideration in evaluating
long-term system resilience, infiltration potential, and maintenance requirements of each
wastewater alternative.
Gravity sewer systems with manholes are more susceptible to saltwater intrusion, infiltration and
inflow (I&I), and corrosion in coastal flood environments. Pressurized systems, including low
pressure sewer systems, utilize fully sealed piping and minimal subsurface structures, which
reduces vulnerability to flood-related infiltration and exfiltration. These factors are considered in
the evaluation of alternatives in Section 6.
Figure 4 - Flood Zone Map
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2.5 WASTEWATER GENERATION
Wastewater generation for the project area was estimated in accordance with County of Hawaiʻi
and City and County of Honolulu wastewater planning criteria and follows the City and County of
Honolulu (CCH), Wastewater System Design Standards dated July 2017 (Standards). Design flows
are based on zoning, assuming occupancy rates, and a per-capita generation rate which follows the
below design criteria:
o Single-family dwelling: 4 capita/unit
o Resort/apartment: 2.8 capita/unit
The tributary area for the proposed improvements includes 77 developed and undeveloped parcels
fronting Aliʻi Drive within the de?ined project limits, see Figure 5- Service Area Map. Population
estimates were prepared for both existing and future conditions. Where dwelling unit counts were
not explicitly known, zoning-based density assumptions were applied. A detailed parcel-level
summary of assumptions and calculations is provided in Appendix A; a high-level summary is
presented in Table 2-1.
Table 2-1 Service Area Count and Estimated Population
Zone # of properties Existing Capita Proposed Capita
RS – 7.5 42 149 161
V – 1.25 35 151 671
Total 77 300 832
Based on these population estimates, wastewater flows were calculated for average day, design,
and peak conditions. The resulting flows are summarized in Table 2-2.
Table 2-2 Summary of Wastewater Flows
Average Day (gpd) Design Flow (gpd) Peak Flow (gpd)
Existing 21,000 31,500 117,241
Future 58,240 87,360 225,902
The wastewater flow assumptions summarized above are applied consistently in Section 5 –
Alternatives Considered. For gravity sewer alternatives, full design flows were used to evaluate
required pipe diameters, depths, hydraulic capacity, and potential susceptibility to infiltration and
inflow (I/I). For pressurized and low-pressure sewer alternatives, reduced I/I potential and
differing flow characteristics were considered, with system capacity governed primarily by pump
performance and pressure conveyance requirements rather than gravity hydraulics.
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Figure 5 – Service Area Map
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3 EXISTING FACILITIES
The COH’s Kailua-Kona Sewer System planning area is divided into two zones. The northern zone
stretches approximately eight miles from Keahole Point to Kailua Bay, while the southern zone
extends about four miles from Kailua Bay to Kahalu‘u Bay, as outlined in the R.M. Towill
Corporation report from April 1981.
The Kealakehe Wastewater Treatment Plant serves this area and has the capacity to treat up to 5.3
million gallons per day (mgd), which is sufficient to manage the sewage generated within the
project area. This ensures that the system can support current and anticipated wastewater
demands effectively.
At the northern end of the project area, the County Sewer System includes an 8-inch sewer line.
There are currently no known issues associated with this segment of the infrastructure, indicating
stable and reliable service in that portion of the system. Based on existing sewer flow as-built
information provided by the County on the Alii Drive Interceptor Sewer & Force Main, Phase III
plans, the normal flow shows the pipe is 60% full and has excess capacity to accommodate
additional flow. Flows to this SMH 17F total 0.47 mgd based on a slope on 0.58%, full flow capacity
is calculated to be 0.70 mgd.
On the southern side of the Project Area is the Keauhou Resort area, which has its own private
wastewater treatment plant. The Keauhou Wastewater Treatment plant is operated by HWS and
has the capacity to treat one million gpd. Their existing service area is provided in the Appendix
and shows the Kahalu‘u sewer pump station (SPS) located in the Kahalu‘u Beach Park, near the
intersection of Ali‘i Drive and Makolea Street. Based on discussions with HWS in 2024, the existing
Kahalu‘u SPS is likely undersized and needs to be updated. The wastewater from this station is
pumped to the Kona Lagoon SPS and then pumped again to get to Keauhou WWTP. The current
capacity of this lift station and the condition of the force main is unknown and would require
further investigation and coordination with HWS.
4 NEED FOR THE PROJECT
Failing onsite wastewater systems within the Project Area present significant environmental and
public health concerns due to the discharge of untreated wastewater to groundwater and
ultimately to Kahaluʻu Bay. This Bay is one of West Hawaiʻi’s most heavily visited coastal areas,
attracting nearly half a million visitors annually, and supports a shallow coral reef ecosystem that
functions as an important nursery habitat for marine life. The bay is also a culturally significant
wahi pana, containing numerous historical and cultural sites along the shoreline.
Given the ecological, cultural, and recreational significance of Kahaluʻu Bay, the Kahaluʻu Bay
Education Center, operated by The Kohala Center in partnership with the County of Hawaiʻi, plays a
key role in promoting reef etiquette, environmental stewardship, and cultural awareness through
daily on-site education programs such as ReefTeach. The Education Center has expressed strong
interest in this project, as protecting nearshore water quality is fundamental to sustaining coral reef
health and supporting its education and stewardship mission.
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Despite evolving regulatory requirements to reduce cesspool use, some properties along continue
to use existing cesspools to discharge untreated wastewater into the subsurface, posing a high risk
of groundwater contamination due to the area’s highly permeable lava rock geology. The Project
Area lies within the Department of Health (DOH)–designated Critical Wastewater Disposal Zone,
where groundwater is known to rapidly migrate to coastal waters. Recent DOH dye-tracing studies
have demonstrated that wastewater discharged from individual cesspools in the area can travel
quickly through the subsurface and discharge directly into Kahaluʻu Bay, con?irming a strong
hydraulic connection between onsite wastewater systems and nearshore waters. These findings
highlight the urgency of addressing cesspool discharges to prevent continued degradation of
groundwater and coastal water quality.
The purpose of the Project is to reduce and ultimately eliminate cesspool-related wastewater
discharges within the Project Area in a cost-effective and timely manner, thereby protecting public
health, recreational uses, and the long-term environmental and cultural integrity of Kahaluʻu Bay.
5 ALTERNATIVES CONSIDERED
Three wastewater collection alternatives were evaluated to provide sewer service to the project
area. Each alternative was developed to convey the design flows described in Section 2.5 and was
assessed for technical feasibility, constructability, cost, operational considerations, and regulatory
complexity. The alternatives include:
• A gravity sewer system connecting to the existing Kahaluʻu lift station operated by Hawaiʻi
Water Service (HWS).
• A gravity sewer system connecting to the County sewer system via a new lift station near the
north end of the project area.
• A low pressure sewer system (LPSS) conveying flow to the County sewer system.
5.1 GRAVITY SEWER SYSTEM
Description
This alternative consists of constructing a gravity sewer system along Aliʻi Drive to collect
wastewater from the project area and convey flow southerly to the existing Kahaluʻu lift station
located near Kahaluʻu Beach Park. Wastewater from the lift station would be pumped via an
existing force main to the Keauhou Wastewater Treatment Plant (WWTP), which is owned and
operated by Hawaiʻi Water Service (HWS).
The gravity sewer alignment generally follows the existing roadway corridor and is designed to
convey the design flows identified in Section 2.5 by gravity to the lift station. This alternative relies
on centralized conveyance and pumping infrastructure, consistent with conventional municipal
wastewater collection systems.
Key infrastructure components associated with this alternative include:
• Approximately 3,400 linear feet of gravity sewer main, anticipated to be 8-inch diameter.
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• Manholes installed at roadway locations to accommodate changes in grade and alignment,
with spacing consistent with County standards.
• Rehabilitation, upgrade, or replacement of the existing Kahaluʻu lift station to accommodate
additional flows from the project area.
• Continued use of the existing force main from the Kahaluʻu lift station to the Keauhou
WWTP.
• Individual service laterals extended to the property line for each parcel within the project
area.
Final pipe sizes, depths, and manhole configurations would be determined during subsequent
design phases.
Regulatory Approval Requirements
Implementation of this alternative would require coordination with HWS because the receiving lift
station, downstream force main, and treatment facility are privately owned and operated. The
parcels along Aliʻi Drive proposed to be served under this alternative are not currently within the
certificated wastewater service area approved for HWS.
Expansion of a privately regulated wastewater utility service area is governed by Hawaiʻi Revised
Statutes Chapter 269 and requires formal approval by the Hawaiʻi Public Utilities Commission
(PUC). This approval is obtained through a petition process that includes agency review, public
notice, potential public hearings, and issuance of a formal Decision and Order by the Commission.
The County does not have the authority to unilaterally expand service through a private
wastewater utility, and approval timelines and outcomes are outside County control.
In addition to PUC approval, this alternative would likely require capacity and wastewater
acceptance, negotiated agreements addressing asset ownership or an asset transfer agreement,
long-term operation and maintenance responsibilities, cost allocation for lift station upgrades or
replacement, and service terms between the County and HWS.
PUC Approval Process
The process flow chart below illustrates the typical steps required to modify a private wastewater
utility’s service area through the PUC approval process.
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The cumulative duration of this process is estimated to be approximately 12 to 18 months, and may
be longer if contested case proceedings, intervenor participation, additional information requests,
or appeals are involved. These durations are inherently uncertain and largely outside the control of
the County. The risk to the County is that PUC decisions are discretionary and subject to public
participation. Members of the public or organizations may intervene or request contested case
hearings, which can substantially extend review timelines. Final approval may also include
conditions related to rates, cost recovery, ownership structure, or operational responsibilities that
could affect project feasibility or increase costs.
As a result, this alternative carries a higher regulatory risk profile compared to alternatives that
connect directly to the County-owned wastewater system and do not require modification of a
private utility service area.
Given that the primary purpose of the Project is to facilitate timely cesspool elimination and reduce
ongoing nutrient and bacteria loading to nearshore waters at Kahaluʻu Bay, multi-year delays
associated with PUC approvals represent a fundamental constraint. Prolonged regulatory timelines
would extend continued cesspool operation within a designated Critical Wastewater Disposal Area,
undermining the environmental and public health objectives of the Project.
Constructability Considerations
Construction of this alternative would involve trench excavation within the Aliʻi Drive roadway
corridor. Gravity sewer installation would require deeper trenches, particularly near the lift station
where pipe depths increase to maintain gravity flow. Excavation depths are anticipated to range
from approximately 4 to 15 feet or greater in localized areas.
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Key constructability considerations include:
• Excavation through hard basalt and lava deposits, potentially requiring rock excavation
methods.
• Increased likelihood of encountering groundwater due to proximity to the shoreline.
• Potential for encountering lava tubes or subsurface voids, which may require stabilization
and specialized backfill methods.
• Placement of manholes and deep excavations within a narrow roadway with significant
vehicular and pedestrian traffic.
• Risk of inadvertent archaeological discoveries, which could affect construction sequencing
and duration.
Construction would be largely confined to the roadway right-of-way, resulting in traffic control
requirements and potential short-term access impacts to adjacent properties.
Cost Considerations
The estimated construction cost for this alternative is approximately $8.1 million, based on
preliminary quantities and unit costs. This estimate includes gravity sewer installation, manholes,
service laterals to the property line, and assumed lift station improvements.
The cost estimate does not include potential costs associated with regulatory approvals, private
utility agreements, or off-site improvements beyond the immediate project scope. These items
would be evaluated and refined during subsequent project phases.
Advantages Disadvantages
Utilizes an existing lift station and downstream
wastewater treatment facilities at Kahaluʻu and Keauhou,
reducing the need for new major treatment infrastructure.
Gravity sewers in coastal shoreline areas are more
susceptible to infiltration and corrosion.
Takes advantage of the general southward slope toward
Kahaluʻu Beach Park, allowing gravity conveyance along
much of the alignment.
Requires 4-15 foot deep trenches, thereby increasing the
risk of encountering lava tubes and ground water.
Provides centralized wastewater collection and treatment
under a single utility operator if ownership is transferred.
May require upgrade or replacement of the existing
Kahaluʻu lift station.
Allows property owners to connect via standard gravity
sewer laterals.
Requires formal approval by the Public Utilities
Commission to expand a privately regulated wastewater
service area, introducing multi-year schedule delays,
public hearing risk, and implementation uncertainty
outside County control.
Requires additional legal coordination and negotiated
agreements related to ownership, operation, and
long-term maintenance of facilities by a private entity.
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5.2 GRAVITY SEWER WITH NEW COUNTY LIFT STATION
Description
This alternative consists of constructing a gravity sewer system along Aliʻi Drive to collect
wastewater from the project area and convey flow to a new County-owned lift station to be
constructed near the north end of the project limits, generally in the vicinity of Queen Kalama
Avenue. From the new lift station, wastewater would be pumped via a new force main to a
downstream County sewer manhole for conveyance to the County wastewater treatment system.
This alternative provides wastewater service entirely within the County of Hawaiʻi system and does
not rely on privately owned wastewater facilities for conveyance or treatment.
Key infrastructure components associated with this alternative include:
• Approximately 3,400 linear feet of gravity sewer main, anticipated to be 8-inch diameter,
installed along Aliʻi Drive.
• Manholes along the alignment to accommodate changes in grade and direction.
• A new wastewater lift station, including wet well, pumps, electrical service, controls, and
appurtenant structures.
• A new 3,400 linear foot force main that would run parallel to the gravity line and would
connect the lift station to an existing County sewer manhole at the north end of the project
area.
• Individual service laterals extended to the property line for each parcel within the project
area.
Final pipe sizes, lift station capacity, force main alignment, and structural configurations would be
determined during subsequent design phases.
All major facilities associated with this alternative would be owned, operated, and maintained by
the County of Hawaiʻi. This alternative does not require coordination with private wastewater
utilities for service area expansion or treatment capacity; however, it would require identification
of a suitable site for the new lift station and acquisition of any necessary easements or property
interests.
Long-term operation and maintenance responsibilities would reside solely with the County,
including electrical power, pump replacement, routine maintenance, and emergency response.
Constructability Considerations
Construction of this alternative would involve both gravity sewer and force main installation within
or adjacent to the Aliʻi Drive roadway corridor, as well as construction of a new lift station facility.
Gravity sewer installation would require trench excavation of similar depth to Alternative 1, with
anticipated excavation depths of approximately 4 to 15 feet or greater in some locations to
maintain gravity flow.
Additional constructability considerations specific to this alternative include:
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• Finding a space to install a new lift station within the project area.
• Deep excavation required to install the lift station wet well and associated structures.
• Excavation through hard basalt and lava rock, potentially requiring rock excavation
equipment and extended construction durations.
• Increased likelihood of encountering groundwater, particularly for deep lift station
excavation near the coastline.
• Installation of two conveyance systems (gravity sewer and force main) within a relatively
narrow roadway corridor, increasing congestion of underground utilities.
• Traffic control, pedestrian safety, and access impacts associated with extended construction
duration in a heavily traveled coastal roadway.
• Potential for inadvertent archaeological discoveries, particularly where deeper excavations
are required for the lift station and sewer structures.
Construction of the lift station would also require staging areas, electrical service installation, and
coordination to minimize impacts to nearby properties and roadway users.
Cost Considerations
The estimated construction cost for this alternative is approximately $10.3 million, reflecting the
additional costs associated with constructing a new lift station and force main in addition to the
gravity sewer system. This estimate includes major conveyance facilities and service laterals to the
property line.
The cost estimate does not include long-term operation and maintenance costs associated with the
new lift station, nor does it account for potential costs related to property acquisition, permitting,
or electrical system upgrades. These elements would be further evaluated and refined during
subsequent project phases.
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Advantages Disadvantages
Connects directly to the County of Hawaiʻi wastewater
system near Queen Kalama Avenue, eliminating reliance
on privately owned wastewater facilities.
Requires installation of deep gravity sewer segments
(approximately 4–15 feet or greater), increasing
excavation complexity and exposure to groundwater and
lava rock.
Consolidates ownership, operation, and maintenance
responsibilities under the County, simplifying long-term
system management and emergency response.
Necessitates construction of a new County-owned lift
station, including deep wet well excavation, electrical
service, and ongoing operational costs.
Utilizes conventional gravity sewer and lift station
infrastructure that is familiar to County maintenance staff.
Includes both gravity sewer and force main pipelines,
resulting in increased construction footprint and
congestion within the narrow Aliʻi Drive roadway
corridor.
Provides standard County sewer lateral connections,
allowing property owners to connect using established
details and procedures.
Higher capital construction cost compared to other
alternatives due to lift station, force main, and electrical
infrastructure.
Avoids the need for Public Utilities Commission approval
and private utility service area expansion.
Requires identification of additional space outside the
roadway right-of-way for lift station installation,
potentially involving easement acquisition.
Continued susceptibility of gravity sewer components to
groundwater infiltration and corrosion in the coastal
environment.
5.3 LOW PRESSURE SEWER SYSTEM (LPSS)
An LPSS collects wastewater from individual parcels within the project area and conveys flow via a
small-diameter pressurized main to a downstream County sewer manhole near the north end of the
project limits, generally in the vicinity of Queen Kalama Avenue.
Under this alternative, wastewater from each parcel would be discharged into the system through a
grinder pump located on private property. Wastewater would be conveyed through a common
pressurized main installed along Aliʻi Drive, ultimately connecting to the County sewer system for
downstream conveyance and treatment.
Key infrastructure components associated with this alternative include:
• Approximately 3,400 linear feet of small-diameter pressurized sewer main, anticipated to
be constructed of high-density polyethylene (HDPE).
• Individual service laterals provided to each parcel, terminating at the property line.
• Privately owned grinder pumps and control panels installed at each parcel to discharge
wastewater into the pressurized system.
• System appurtenances such as isolation valves and cleanouts required for pressurized
operation.
• Connection to an existing County sewer manhole for downstream conveyance.
Final pipe sizing, system pressures, and appurtenance requirements would be determined during
subsequent design phases.
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The mainline LPSS infrastructure would be owned and maintained by the County of Hawaiʻi, while
grinder pumps, electrical connections, and associated controls would be the responsibility of
individual property owners. This alternative would require development of clear standards and
mechanisms to address private equipment installation, operation, maintenance, and replacement.
This alternative does not require coordination with private wastewater utilities for service area
expansion and would operate entirely within the County sewer system. However, long-term
administration would require procedures to address homeowner compliance, pump failures, power
outages, and COH training and staffing for this new system.
Constructability Considerations
Construction of the LPSS alternative would involve installation of shallow pressurized mains within
the Aliʻi Drive roadway corridor. Because the system does not rely on gravity ?low, trench depths
are generally shallower than those required for gravity sewer systems, typically on the order of 4 to
5 feet. Constructability considerations for this alternative include:
• Reduced excavation depth and volume compared to gravity sewer alternatives, resulting in
less exposure to groundwater.
• Increased flexibility to navigate around existing underground utilities due to the absence of
slope constraints with a pressurized system versus a gravity system.
• Fewer large structures, such as manholes or deep excavations, reducing disruption within
the narrow roadway corridor.
• Continued need for trench excavation through hard basalt and lava rock, though at
shallower depths.
• Installation of service laterals to each parcel, which may require coordination where access
easements or shared driveways exist.
Construction impacts would largely be confined to the roadway right-of-way, with reduced
excavation duration relative to gravity sewer alternatives.
Cost Considerations
The estimated construction cost for this alternative is approximately $4.8 million, reflecting
reduced excavation depth, smaller pipe diameters, and the absence of large structures such as lift
stations or manholes.
In addition to the County’s construction costs, this alternative would require individual property
owners to purchase and install grinder pump units and associated electrical connections. These
private costs are not included in the County construction estimate. Long-term operational costs
associated with pump maintenance, replacement, and electrical usage would also be borne by
homeowners.
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Advantages Disadvantages
Uses shallow‑installed, small‑diameter pressurized piping
(typically 4–5 feet deep), significantly reducing excavation
depth and subsurface risk.
Requires installation of a grinder pump and associated
electrical service at each parcel, shifting a portion of
capital and operational costs to property owners.
Pressurized, fully sealed system minimizes groundwater
infiltration, saltwater intrusion, and corrosion.
Long‑term system performance depends on homeowner
compliance, proper pump operation, and timely
equipment maintenance.
Flexible pipe alignment allows avoidance of utilities, lava
tubes, groundwater, and archaeological resources.
County maintenance staff may require additional training
or resources to manage a pressurized collection system.
Eliminates manholes and major underground structures
within the roadway corridor.
System operation is affected by power outages, requiring
homeowner awareness and operational safeguards.
Lowest estimated County capital construction cost of the
evaluated alternatives.
Higher distributed operational responsibility compared to
centralized gravity systems.
Connects directly to the County sewer system without
requiring PUC approval or coordination with private
wastewater utilities.
5.4 COMPARATIVE EVALUATION OF ALTERNATIVES
The three alternatives described in Sections 5.1 through 5.3 were evaluated based on technical
design criteria, constructability, cost considerations, and long-term operations and maintenance
(O&M). Each alternative is capable of conveying the design flows identified in Section 2.5; however,
the alternatives differ substantially with respect to system configuration, construction complexity,
cost distribution, and long-term operational responsibility.
Technical Design Criteria
All three alternatives are technically feasible for conveying wastewater flows generated by the
project area and connecting to an existing downstream wastewater treatment system. Key technical
distinctions among the alternatives are related to hydraulic functionality, infiltration susceptibility,
and system resilience.
The gravity sewer alternatives (Alternatives 1 and 2) rely on deep gravity conveyance and
centralized pumping facilities to transport wastewater. These systems are proven and widely used
but are inherently more susceptible to groundwater infiltration, particularly in coastal
environments where groundwater levels are elevated and trench depths are significant. Both
gravity alternatives also require multiple manholes and deep structures, which introduce additional
locations for potential inflow and infiltration.
The LPSS (Alternative 3) conveys wastewater through pressurized mains and does not rely on
gravity hydraulics. As a result, it offers reduced potential for infiltration and exfiltration and greater
flexibility in pipe alignment. Pressurized conveyance also allows the system to more readily
accommodate variations in topography and utility conflicts without increasing pipe depth.
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Constructability
Constructability represents a key differentiating factor among the alternatives due to site-specific
conditions along Aliʻi Drive, including narrow roadway widths, high pedestrian and vehicular
traffic, proximity to the shoreline, and subsurface conditions characterized by basalt and potential
lava tubes.
Alternatives 1 and 2 require installation of gravity sewers at relatively deep depths to maintain
hydraulic grade, resulting in:
• Increased excavation volumes and duration within the roadway.
• Higher likelihood of encountering groundwater during construction.
• Elevated risk of encountering lava tubes, subsurface voids, or archaeological resources.
• Greater disruption to traffic and adjacent properties due to extended construction
timelines.
Alternative 2 presents additional constructability challenges beyond those associated with
Alternative 1 due to construction of a new lift station, which requires deep excavation for a wet
well, installation of electrical and control systems, and site development within or adjacent to the
roadway corridor.
Alternative 3 (LPSS) generally requires shallower trenches and smaller-diameter pipes, reducing
excavation depth and duration. The absence of large structures such as manholes or lift stations
within the roadway corridor simplifies construction sequencing and reduces exposure to
subsurface and archaeological risk. However, this alternative requires coordination at each parcel
to install private grinder pumps and laterals, which may introduce localized construction impacts
on private property.
Cost Considerations
Construction costs for the three alternatives vary notably and reflect differences in excavation
depth, pipe size, and required structures.
• Alternative 1 has a moderate estimated construction cost and includes gravity sewer
installation and improvements to an existing lift station. Some costs and risks are associated
with coordinating upgrades to privately owned infrastructure.
• Alternative 2 has the highest estimated construction cost, driven by the need to construct a
new County-owned lift station and force main in addition to the gravity sewer system.
• Alternative 3 has the lowest estimated County construction cost, primarily due to shallower
trenching, smaller pipe diameters, and elimination of lift stations and large structures.
While Alternative 3 reduces County capital costs, a portion of capital and ongoing costs would be
transferred to property owners for grinder pump installation, electrical upgrades, and equipment
replacement. These private costs are not reflected in the County construction estimate but are an
important consideration for implementation and public acceptance.
June 2026 PER - ALIʻI DRIVE SEWER LINE EXTENSION 20
Operations, Maintenance and Risk
Long-term operations and maintenance responsibilities differ significantly among the alternatives
and influence overall system risk and lifecycle performance.
Under Alternatives 1 and 2, wastewater collection, pumping, and conveyance are centralized under
a single utility operator. Centralized systems simplify oversight, maintenance scheduling, and
emergency response; however, lift stations introduce ongoing energy use, mechanical maintenance,
and vulnerability during power outages. Alternative 1 further relies on long-term coordination with
a private utility, which may introduce administrative and contractual complexity.
Alternative 3 decentralizes a portion of system operations by requiring individual homeowners to
operate and maintain grinder pumps. While the pressurized collection system minimizes
infiltration and reduces County maintenance responsibilities for large facilities, this approach
introduces risks related to homeowner compliance, power outages, and equipment failure.
Successful implementation would require clear standards, enforcement mechanisms, and public
education to ensure long-term system reliability and protection of public health.
6 SELECTION / RECOMMENDED ALTERNATIVE
Based on the evaluation of constructability, environmental risk, cost, regulatory complexity, and
long-term system resilience, the Low Pressure Sewer System (Alternative 3) is recommended for
implementation.
The Low Pressure Sewer System (LPSS) alternative utilizes shallow-installed, small-diameter
pressurized piping with individual service laterals connected to grinder pumps located on each
property. This system does not rely on continuous gravity slope, allowing the pipeline to rise or fall
as needed to avoid conflicts with existing utilities, lava tubes, groundwater, and archaeological
features.
The LPSS alternative offers several advantages in the Aliʻi Drive coastal environment:
• Significantly reduced excavation depths (typically 4 to 5 feet)
• Elimination of manholes and major underground structures
• Minimal potential for groundwater infiltration or saltwater intrusion due to fully
pressurized, sealed piping
• Improved resilience to coastal flooding and long-term sea-level rise
• Reduced construction footprint and shorter construction duration compared to gravity
alternatives
The LPSS alternative also has the lowest estimated capital construction cost of the three options
and avoids the need for Public Utilities Commission approvals or coordination with private
wastewater utilities.
The primary tradeoff associated with LPSS is the requirement for grinder pumps at each parcel.
This introduces considerations related to homeowner responsibility, power availability, and long-
June 2026 PER - ALIʻI DRIVE SEWER LINE EXTENSION 21
term maintenance oversight, which would require clear policy direction, public outreach, and
potential ordinance or programmatic support by the County.
7 FUNDING SOURCES
The Aliʻi Drive Sewer Line Extension project is well positioned to secure state and federal funding
due to its direct support of cesspool elimination, groundwater protection, and improvement of
nearshore water quality. These outcomes align closely with statewide wastewater management
priorities and regulatory requirements addressing the environmental and public health impacts of
unmanaged wastewater discharges in coastal areas.
The primary funding mechanism for the project is expected to be the Hawaiʻi Clean Water State
Revolving Fund (CWSRF), which provides low-interest financing for wastewater infrastructure
projects that protect public health and prevent contamination of groundwater and coastal waters.
This project is a strong candidate for CWSRF funding because it enables connection to a centralized
sewer system, reduces untreated wastewater discharges, and addresses documented impacts
within a designated critical wastewater disposal area. Inclusion in the State’s Intended Use Plan will
be required to secure funding.
In addition to base financing, the project may qualify for CWSRF additional subsidization, including
principal forgiveness, based on its public health benefits, environmental significance, and potential
to reduce the financial burden on residential users. Similar wastewater and cesspool conversion
projects in Hawaiʻi have received subsidized funding under recent program cycles, indicating strong
alignment with current funding priorities. Supplemental funding sources, such as USDA Rural
Development programs, may also be considered to address affordability or funding gaps depending
on eligibility and program requirements.
A comparable funding approach was implemented for the Lono Kona project, where the County
constructed a gravity sewer system serving approximately 112 parcels across 43 acres using a
combination of USDA grant and loan funding. While a portion of the project costs was covered
through grant funding, the remaining loan component was structured for long-term repayment by
benefiting property owners over a 35-year period, demonstrating a viable model for balancing
public investment with user-based financing.
The recommended LPSS alternative supports the overall funding strategy by providing a lower
capital construction cost and a scalable approach to implementation. The reduced cost, combined
with its ability to accelerate cesspool elimination and minimize environmental impacts, strengthens
the project’s competitiveness for available funding and improves overall feasibility. Additional
considerations include managing the distribution of costs between the County and property
owners, particularly for grinder pump installation, which may influence funding structure and
program implementation.
June 2026 PER - ALIʻI DRIVE SEWER LINE EXTENSION 22
8 CONCLUSIONS AND RECOMMENDATIONS
The Aliʻi Drive Sewer Line Extension is needed to eliminate existing cesspools, comply with State of
Hawaiʻi wastewater regulations, and reduce ongoing impacts to nearshore water quality within the
Kahaluʻu coastal environment. Evaluation of multiple wastewater collection alternatives indicates
that conventional gravity sewer systems present substantial constructability, environmental, and
regulatory challenges in this corridor.
The LPSS alternative offers a technically sound and resilient solution that minimizes excavation,
reduces risk to groundwater and marine waters, and can be implemented more efficiently than
gravity-based alternatives. While LPSS introduces operational considerations related to distributed
grinder pumps, these challenges can be addressed through clear program structure, homeowner
education, and establishment of appropriate County policies.
The project is well positioned to pursue CWSRF financing, including potential subsidization, due to
its demonstrated public health benefits, environmental significance, and consistency with statewide
cesspool conversion goals. Supplemental funding sources, such as USDA Rural Development
programs, may also be considered to improve affordability and support implementation. Inclusion
of the project in the State’s Intended Use Plan will be an important step in securing funding and
advancing the project toward design and construction
It is recommended that the County of Hawaiʻi Department of Environmental Management proceed
with the LPSS alternative and advance the project into the next phase of design. Implementation
should include development of a funding strategy coordinated with design progression, refinement
of project costs, development of a LPSS design standard, and evaluation of mechanisms to address
homeowner participation and affordability. Advancing the LPSS alternative, supported by a
coordinated funding approach, represents the most effective and achievable path forward for
meeting the project’s environmental and public health objectives within the Aliʻi Drive corridor.
June 2026 PER - ALIʻI DRIVE SEWER LINE EXTENSION 23
Sewer System Comparison
Category Option 1 – Gravity
Sewer to HWS
Option 2 – Gravity
Sewer with New
County Lift Station
Option 3 – Low
Pressure Sewer
System (LPSS)
Connection to Existing HWS lift station at
Kahaluʻu Beach Park; flow
conveyed to Keauhou
WWTP
New County-owned lift
station discharging to
County sewer system near
Queen Kalama Ave.
County sewer system via
pressurized connection
near Queen Kalama Ave.
System Ownership Private utility (Hawaiʻi
Water Service), subject to
negotiated transfer
agreements
County of Hawaiʻi
County of Hawaiʻi, private
ownership of grinder
pumps
Lateral Connection County Standard Detail
WW-2
County Standard Detail
WW-2
Pressurized lateral with
isolation valve and check
valve
Collection System Type Gravity sewer with
centralized lift station
Gravity sewer with new lift
station and force main
Pressurized small-diameter
collection system
Pipe Type/Size (mainline) 8” PVC,
6” PVC laterals
8”PVC,
6” PVC laterals
4” HDPE,
1-1/4” lateral connections
Typical Installation Depth 4-15 feet 4-15 feet Shallow installation
4-5 feet
Structures Manholes, existing lift
station upgrades
Manholes, new lift station,
and force main
None within roadway
Estimated County
Construction Cost
$8,100,000 $10,300,000 $4,800,000
Estimated Homeowner
Costs
Cesspool closure and
plumbing connection
Est $20k to $40k
Cesspool closure and
plumbing connection.
some properties may still
require a grinder pump and
electrical upgrades
Est $20k to $62k
Cesspool closure, plumbing
connection, grinder pump,
and electrical upgrades
Est $36k to $62k
Annual Homeowners
Electricity Costs
$0 for most, ~$80/year
where a grinder pump is
required
$0 for most, ~$80/year
where a grinder pump is
required
~$80/year per property
for grinder pump operation
Wastewater Service
Charges
HWS Utility Rates COH Rates COH Rates
Estimated Implementation
Timeline
4-6 years
Driven by required Public
Utilities Commission (PUC)
approval and private utility
coordination
4-7 years
Subject to design, land
acquisition, and
construction
3-4 years
Subject to design,
homeowner coordination,
and construction
Construction Impacts Long-term roadway
impacts; deep excavation;
work adjacent to Kahaluʻu
Beach Park
Long-term roadway
impacts; deep excavation;
additional area needed for
lift station
Reduced roadway impacts;
shallower trenches; shorter
construction duration
Operations and
Maintenance
Operated by HWS following
transfer; dependent on
private utility coordination
County of Hawaiʻi
responsible for lift station
O&M
County responsible for
main system; homeowners
responsible for grinder
pumps
Lifecycle Costs HWS to maintain 20-30 years 50 years
June 2026 PER - ALIʻI DRIVE SEWER LINE EXTENSION 24
REFERENCES
ASM Affiliates, Inc. Archaeological Literature Review and Field Inspection for the Aliʻi Drive Sewer
Line Extension Project. July 2025.
Belt Collins Hawaiʻi LLC, in association with PBR Hawaiʻi & Associates, Inc. Environmental Report:
Lono Kona Sewer Improvements District. Prepared for the County of Hawaiʻi, Department of
Environmental Management, 2012.
City and County of Honolulu. Wastewater System Design Standards. Honolulu, HI, July 2017.
Appendix A
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4814
SUBJECT: Existing Wastewater Generation BY:EI/KM
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer
TMK Zone Area (ac)Area (sf)
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
377010001 RS-7.5 0.01 339 0 4 0 0 0.0 2.5 0 0 0 0 23 23
377010002 RS-7.5 0.39 17001 n/a n/a4 3 210 0.5 2.5 525 105 315 630 1073 1703
377010004 RS-7.5 0.21 9248 n/a n/a4 3 210 0.5 2.5 525 105 315 630 584 1214
377010005 RS-7.5 0.13 5558 0 4 0 0 0.0 2.5 0 0 0 0 351 351
377010006 RS-7.5 0.09 4091 1 4 4 280 0.7 2.5 700 140 420 840 282 1122
377010007 RS-7.5 0.09 3828 1 4 4 280 0.7 2.5 700 140 420 840 264 1104
377010008 RS-7.5 0.42 18221 1 4 4 280 0.7 2.5 700 140 420 840 1255 2095
377010076 RS-7.5 0.02 914 0 4 0 0 0.0 2.5 0 0 0 0 58 58
378014003 V-1.25 0.21 9179 0 2.8 0 0 0.0 2.5 0 0 0 0 580 580
378014004 V-1.25 0.15 6342 0 2.8 0 0 0.0 2.5 0 0 0 0 400 400
378014005 V-1.25 0.23 9986 0 2.8 0 0 0.0 2.5 0 0 0 0 630 630
378014006 RS-7.5 0.24 10446 2 4 8 560 1.4 2.5 1400 280 840 1680 660 2340
378014007 V-1.25 0.06 2706 1 2.8 3.0 210 0.5 2.5 525 105 315 630 171 801
378014008 RS-7.5 0.14 6092 n/a n/a4 3 210 0.5 2.5 525 105 315 630 385 1015
378014009 V-1.25 0.23 9803 1 2.8 3 210 0.5 2.5 525 105 315 630 619 1249
378014010 V-1.25 0.11 4800 1 2.8 3 210 0.5 2.5 525 105 315 630 303 933
378014011 V-1.25 0.17 7240 1 2.8 3 210 0.5 2.5 525 105 315 630 457 1087
378014012 V-1.25 0.06 2790 1 2.8 3 210 0.5 2.5 525 105 315 630 176 806
378014013 V-1.25 0.37 16324 0 2.8 0 0 0.0 2.5 0 0 0 0 1031 1031
378014015 V-1.25 0.25 10854 n/a n/a4 14 980 2.5 2.5 2450 490 1470 2940 685 3625
378014016 V-1.25 0.23 9979 n/a n/a4 14 980 2.5 2.5 2450 490 1470 2940 630 3570
378014019 V-1.25 0.38 16449 1 2.8 3 210 0.5 2.5 525 105 315 630 1038 1668
378014020 V-1.25 0.10 4426 0 2.8 0 0 0.0 2.5 0 0 0 0 279 279
378014021 RS-7.5 0.67 29273 0 4 0 0 0.0 2.5 0 0 0 0 1848 1848
378014022 RS-7.5 0.11 4625 1 4 4 280 0.7 2.5 700 140 420 840 292 1132
378014023 RS-7.5 0.03 1502 1 4 4 280 0.7 2.5 700 140 420 840 95 935
378014024 V-1.25 0.15 6618 n/a n/a4 7 490 1.2 2.5 1225 245 735 1470 418 1888
378014025 V-1.25 0.17 7357 1 2.8 3 210 0.5 2.5 525 105 315 630 464 1094
378014027 V-1.25 0.08 3309 0 2.8 0 0 0.0 2.5 0 0 0 0 228 228
378014028 V-1.25 0.02 907 0 2.8 0 0 0.0 2.5 0 0 0 0 62 62
378014029 V-1.25 0.19 8436 n/a n/a4 8 560 1.4 2.5 1400 280 840 1680 581 2261
378014030 V-1.25 0.44 19087 1 2.8 3 210 0.5 2.5 525 105 315 630 1315 1945
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4814
SUBJECT: Existing Wastewater Generation BY:EI/KM
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer
TMK Zone Area (ac)Area (sf)
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
378014032 V-1.25 0.47 20298 2 2.8 6 420 1.1 2.5 1050 210 630 1260 1398 2658
378014033 V-1.25 0.36 15658 3 2.8 9 630 1.6 2.5 1575 315 945 1890 1078 2968
378014034 V-1.25 0.57 24695 1 2.8 3 210 0.5 2.5 525 105 315 630 1701 2331
378014035 V-1.25 0.35 15268 3 2.8 9 630 1.6 2.5 1575 315 945 1890 1051 2941
378014036 V-1.25 0.39 17121 n/a n/a4 31 2170 5.4 2.5 5425 1085 3255 6510 1179 7689
378014037 V-1.25 0.14 6152 0 2.8 0 0 0.0 2.5 0 0 0 0 424 424
378014038 V-1.25 0.12 5319 n/a n/a4 5 350 0.9 2.5 875 175 525 1050 366 1416
378014039 V-1.25 0.17 7330 1 2.8 3 210 0.5 2.5 525 105 315 630 505 1135
378014040 V-1.25 0.24 10505 1 2.8 3 210 0.5 2.5 525 105 315 630 723 1353
378014041 V-1.25 0.13 5578 1 2.8 3 210 0.5 2.5 525 105 315 630 384 1014
378014043 V-1.25 0.21 9292 0 2.8 0 0 0.0 2.5 0 0 0 0 640 640
378014044 V-1.25 0.14 6082 1 2.8 3 210 0.5 2.5 525 105 315 630 419 1049
378014045 V-1.25 0.93 40334 0 2.8 0 0 0.0 2.5 0 0 0 0 2778 2778
378014048 V-1.25 0.05 2241 1 2.8 3 210 0.5 2.5 525 105 315 630 141 771
378014050 RS-7.5 0.22 9536 1 4 4 280 0.7 2.5 700 140 420 840 602 1442
378014051 RS-7.5 0.13 5785 1 4 4 280 0.7 2.5 700 140 420 840 365 1205
378014052 RS-7.5 0.19 8151 1 4 4 280 0.7 2.5 700 140 420 840 515 1355
378014053 RS-7.5 0.25 10902 1 4 4 280 0.7 2.5 700 140 420 840 688 1528
378014054 RS-7.5 0.32 14099 n/a n/a4 6 420 1.1 2.5 1050 210 630 1260 890 2150
378014055 RS-7.5 0.43 18777 1 4 4 280 0.7 2.5 700 140 420 840 1185 2025
378014056 RS-7.5 1.61 70261 0 4 0 0 0.0 2.5 0 0 0 0 4436 4436
378014062 RS-7.5 0.26 11500 1 4 4 280 0.7 2.5 700 140 420 840 726 1566
378014063 RS-7.5 0.26 11488 1 4 4 280 0.7 2.5 700 140 420 840 725 1565
378014064 RS-7.5 0.03 1182 1 4 4 280 0.7 2.5 700 140 420 840 75 915
378014065 RS-7.5 0.27 11923 1 4 4 280 0.7 2.5 700 140 420 840 753 1593
378014066 RS-7.5 0.28 12222 1 4 4 280 0.7 2.5 700 140 420 840 772 1612
378014067 RS-7.5 0.28 11988 1 4 4 280 0.7 2.5 700 140 420 840 757 1597
378014068 RS-7.5 0.28 12395 1 4 4 280 0.7 2.5 700 140 420 840 782 1622
378014069 RS-7.5 0.27 11687 1 4 4 280 0.7 2.5 700 140 420 840 738 1578
378014070 RS-7.5 0.27 11660 1 4 4 280 0.7 2.5 700 140 420 840 736 1576
378014071 RS-7.5 0.26 11308 1 4 4 280 0.7 2.5 700 140 420 840 714 1554
378014072 RS-7.5 0.26 11425 1 4 4 280 0.7 2.5 700 140 420 840 721 1561
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4814
SUBJECT: Existing Wastewater Generation BY:EI/KM
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer
TMK Zone Area (ac)Area (sf)
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
378014074 RS-7.5 0.07 2936 1 4 4 280 0.7 2.5 700 140 420 840 185 1025
378014075 RS-7.5 0.16 6825 1 4 4 280 0.7 2.5 700 140 420 840 431 1271
378014076 RS-7.5 0.24 10496 1 4 4 280 0.7 2.5 700 140 420 840 663 1503
378014077 RS-7.5 0.34 14807 1 4 4 280 0.7 2.5 700 140 420 840 935 1775
378014078 RS-7.5 0.20 8740 n/a n/a4 3 210 0.5 2.5 525 105 315 630 552 1182
378014079 RS-7.5 0.20 8730 1 4 4 280 0.7 2.5 700 140 420 840 551 1391
378014080 RS-7.5 0.18 7752 1 4 4 280 0.7 2.5 700 140 420 840 489 1329
378014081 RS-7.5 0.18 8026 n/a n/a4 3 210 0.5 2.5 525 105 315 630 507 1137
378014082 RS-7.5 0.21 9115 1 4 4 280 0.7 2.5 700 140 420 840 575 1415
378014083 RS-7.5 0.16 7098 1 4 4 280 0.7 2.5 700 140 420 840 448 1288
378014084 RS-7.5 0.13 5818 1 4 4 280 0.7 2.5 700 140 420 840 367 1207
378014085 V-1.25 0.44 19353 1 2.8 3 210 0.5 2.5 525 105 315 630 1333 1963
378014095 V-1.25 0.33 14527 1 2.8 3 210 0.5 2.5 525 105 315 630 1000 1630
TOTAL 21000 52.5 192.5 52500 10500 31500 63000 54241 117241
300 <-- # Capita 105.0 117,241
77 <-- # Parcels
Design Parameters
1 Sewers laid above the ground water table
Groundwater Infiltration 35 gpcd
Wet I/I 3000 gad
2 Average per capita design flow =70 gpd
3 Equivalent Populations by zoning
A-5a Agricultural, 5 ac/unit, assume 25 capita / ac
RS-7.5 Single Family Residential , 7,500 sf/unit, 4 capita / unit
V-1.25 Multiple Family Residential, 1250 sf/unit, 2.8 capita / unit (rounded up)
4 Variable use. See captia estimation by parcel.
5 Equivalent Dwelling Unit =400 gpd
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4568 23 SFR
SUBJECT: Proposed Wastewater Generation BY:EI/KM 2 Multi Family
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer 1 Open
TMK Zone Area (ac)Area (sf)
Proposed
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
377010001 RS-7.5 0.01 339 0 4 0 0 0.0 2.5 0 0 0 0 23 23
377010002 RS-7.5 0.39 17001 2 n/a4 3 210 0.5 2.5 525 105 315 630 1073 1703
377010004 RS-7.5 0.21 9248 1 n/a4 3 210 0.5 2.5 525 105 315 630 584 1214
377010005 RS-7.5 0.13 5558 0 4 0 0 0.0 2.5 0 0 0 0 351 351
377010006 RS-7.5 0.09 4091 0 4 0 0 0.0 2.5 0 0 0 0 0 0
377010007 RS-7.5 0.09 3828 0 4 0 0 0.0 2.5 0 0 0 0 264 264
377010008 RS-7.5 0.42 18221 2 4 8 560 1.4 2.5 1400 280 840 1680 1255 2935
377010076 RS-7.5 0.02 914 0 4 0 0 0.0 2.5 0 0 0 0 58 58
378014003 V-1.25 0.21 9179 7 3 20 1400 3.5 2.5 3500 700 2100 4200 580 4780
378014004 V-1.25 0.15 6342 5 3 14 980 2.5 2.5 2450 490 1470 2940 400 3340
378014005 V-1.25 0.23 9986 7 3 20 1400 3.5 2.5 3500 700 2100 4200 630 4830
378014006 RS-7.5 0.24 10446 1 4 4 280 0.7 2.5 700 140 420 840 660 1500
378014007 V-1.25 0.06 2706 2 3 6 420 1.1 2.5 1050 210 630 1260 171 1431
378014008 RS-7.5 0.14 6092 0 n/a4 3 210 0.5 2.5 525 105 315 630 385 1015
378014009 V-1.25 0.23 9803 7 3 20 1400 3.5 2.5 3500 700 2100 4200 619 4819
378014010 V-1.25 0.11 4800 3 3 9 630 1.6 2.5 1575 315 945 1890 303 2193
378014011 V-1.25 0.17 7240 5 3 14 980 2.5 2.5 2450 490 1470 2940 457 3397
378014012 V-1.25 0.06 2790 2 3 6 420 1.1 2.5 1050 210 630 1260 176 1436
378014013 V-1.25 0.37 16324 13 3 37 2590 6.5 2.5 6475 1295 3885 7770 1031 8801
378014015 V-1.25 0.25 10854 8 n/a4 14 980 2.5 2.5 2450 490 1470 2940 685 3625
378014016 V-1.25 0.23 9979 7 n/a4 14 980 2.5 2.5 2450 490 1470 2940 630 3570
378014019 V-1.25 0.38 16449 13 3 37 2590 6.5 2.5 6475 1295 3885 7770 1038 8808
378014020 V-1.25 0.10 4426 3 3 9 630 1.6 2.5 1575 315 945 1890 279 2169
378014021 RS-7.5 0.67 29273 3 4 12 840 2.1 2.5 2100 420 1260 2520 1848 4368
378014022 RS-7.5 0.11 4625 0 4 0 0 0.0 2.5 0 0 0 0 292 292
378014023 RS-7.5 0.03 1502 0 4 0 0 0.0 2.5 0 0 0 0 95 95
378014024 V-1.25 0.15 6618 5 n/a4 7 490 1.2 2.5 1225 245 735 1470 418 1888
378014025 V-1.25 0.17 7357 5 3 14 980 2.5 2.5 2450 490 1470 2940 464 3404
378014027 V-1.25 0.08 3309 2 3 6 420 1.1 2.5 1050 210 630 1260 228 1488
378014028 V-1.25 0.02 907 0 3 0 0 0.0 2.5 0 0 0 0 62 62
378014029 V-1.25 0.19 8436 6 n/a4 8 560 1.4 2.5 1400 280 840 1680 581 2261
378014030 V-1.25 0.44 19087 15 3 42 2940 7.4 2.5 7350 1470 4410 8820 1315 10135
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4568 23 SFR
SUBJECT: Proposed Wastewater Generation BY:EI/KM 2 Multi Family
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer 1 Open
TMK Zone Area (ac)Area (sf)
Proposed
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
378014032 V-1.25 0.47 20298 16 3 45 3150 7.9 2.5 7875 1575 4725 9450 1398 10848
378014033 V-1.25 0.36 15658 12 3 34 2380 6.0 2.5 5950 1190 3570 7140 1078 8218
378014034 V-1.25 0.57 24695 19 3 54 3780 9.5 2.5 9450 1890 5670 11340 1701 13041
378014035 V-1.25 0.35 15268 12 3 36 2520 6.3 2.5 6300 1260 3780 7560 1051 8611
378014036 V-1.25 0.39 17121 13 n/a4 31 2170 5.4 2.5 5425 1085 3255 6510 1179 7689
378014037 V-1.25 0.14 6152 4 3 12 840 2.1 2.5 2100 420 1260 2520 424 2944
378014038 V-1.25 0.12 5319 4 n/a4 5 350 0.9 2.5 875 175 525 1050 366 1416
378014039 V-1.25 0.17 7330 5 3 14 980 2.5 2.5 2450 490 1470 2940 505 3445
378014040 V-1.25 0.24 10505 8 3 23 1610 4.0 2.5 4025 805 2415 4830 723 5553
378014041 V-1.25 0.13 5578 4 3 12 840 2.1 2.5 2100 420 1260 2520 384 2904
378014043 V-1.25 0.21 9292 7 3 20 1400 3.5 2.5 3500 700 2100 4200 640 4840
378014044 V-1.25 0.14 6082 4 3 12 840 2.1 2.5 2100 420 1260 2520 419 2939
378014048 V-1.25 0.05 2241 1 3 3 210 0.5 2.5 525 105 315 630 141 771
378014050 RS-7.5 0.22 9536 1 4 4 280 0.7 2.5 700 140 420 840 602 1442
378014051 RS-7.5 0.13 5785 0 4 0 0 0.0 2.5 0 0 0 0 365 365
378014052 RS-7.5 0.19 8151 1 4 4 280 0.7 2.5 700 140 420 840 515 1355
378014053 RS-7.5 0.25 10902 1 4 4 280 0.7 2.5 700 140 420 840 688 1528
378014054 RS-7.5 0.32 14099 1 n/a4 6 420 1.1 2.5 1050 210 630 1260 890 2150
378014055 RS-7.5 0.43 18777 2 4 8 560 1.4 2.5 1400 280 840 1680 1185 2865
378014056 RS-7.5 1.61 70261 9 4 36 2520 6.3 2.5 6300 1260 3780 7560 4436 11996
378014062 RS-7.5 0.26 11500 1 4 4 280 0.7 2.5 700 140 420 840 726 1566
378014063 RS-7.5 0.26 11488 1 4 4 280 0.7 2.5 700 140 420 840 725 1565
378014064 RS-7.5 0.03 1182 0 4 0 0 0.0 2.5 0 0 0 0 75 75
378014065 RS-7.5 0.27 11923 1 4 4 280 0.7 2.5 700 140 420 840 753 1593
378014066 RS-7.5 0.28 12222 1 4 4 280 0.7 2.5 700 140 420 840 772 1612
378014067 RS-7.5 0.28 11988 1 4 4 280 0.7 2.5 700 140 420 840 757 1597
378014068 RS-7.5 0.28 12395 1 4 4 280 0.7 2.5 700 140 420 840 782 1622
378014069 RS-7.5 0.27 11687 1 4 4 280 0.7 2.5 700 140 420 840 738 1578
378014070 RS-7.5 0.27 11660 1 4 4 280 0.7 2.5 700 140 420 840 736 1576
378014071 RS-7.5 0.26 11308 1 4 4 280 0.7 2.5 700 140 420 840 714 1554
378014072 RS-7.5 0.26 11425 1 4 4 280 0.7 2.5 700 140 420 840 721 1561
378014074 RS-7.5 0.07 2936 0 4 0 0 0.0 2.5 0 0 0 0 185 185
PROJECT: Ali'i Drive Sewer JOB NO:24A0108.00
CLIENT: DEM DATE:46142.4568 23 SFR
SUBJECT: Proposed Wastewater Generation BY:EI/KM 2 Multi Family
FILE:T:\COH_AliiDrSewer\24A0108_00\04BasisOfDesign\Analyses\Sewer 1 Open
TMK Zone Area (ac)Area (sf)
Proposed
Dwelling
Units
Capita per
acre or unit Capita
Average
Wastewater
Flow (gpd)
Equivalent
Dwelling Unit
Peaking
Factor
Peak Base
Sanitary
Flow
Groundwa
ter
Infiltration
Design
Average
Flow (gpd)
Peak Dry
Weather
Flow
Wet Weather
Infiltration/Infl
ow (gpd)
Design Peak
Flow (gpd)
378014075 RS-7.5 0.16 6825 0 4 0 0 0.0 2.5 0 0 0 0 431 431
378014076 RS-7.5 0.24 10496 1 4 4 280 0.7 2.5 700 140 420 840 663 1503
378014077 RS-7.5 0.34 14807 1 4 4 280 0.7 2.5 700 140 420 840 935 1775
378014078 RS-7.5 0.20 8740 1 n/a4 3 210 0.5 2.5 525 105 315 630 552 1182
378014079 RS-7.5 0.20 8730 1 4 4 280 0.7 2.5 700 140 420 840 551 1391
378014080 RS-7.5 0.18 7752 1 4 4 280 0.7 2.5 700 140 420 840 489 1329
378014081 RS-7.5 0.18 8026 1 n/a4 3 210 0.5 2.5 525 105 315 630 507 1137
378014082 RS-7.5 0.21 9115 1 4 4 280 0.7 2.5 700 140 420 840 575 1415
378014083 RS-7.5 0.16 7098 0 4 0 0 0.0 2.5 0 0 0 0 448 448
378014084 RS-7.5 0.13 5818 0 4 0 0 0.0 2.5 0 0 0 0 367 367
378014085 V-1.25 0.44 19353 15 3 42 2940 7.4 2.5 7350 1470 4410 8820 1333 10153
378014095 V-1.25 0.33 14527 11 3 31 2170 5.4 2.5 5425 1085 3255 6510 1000 7510
58240 145.6 190 145600 29120 87360 174720 51182 225902
76 <-- # Parcels 832 <-- # Capita 225902
Design Parameters
1 Sewers laid above the ground water table
Groundwater Infiltration 35 gpcd
Wet I/I 3000 gad
2 Average per capita design flow =70 gpd
3 Equivalent Populations by zoning
A-5a Agricultural, 5 ac/unit, assume 25 capita / ac
RS-7.5 Single Family Residential , 7,500 sf/unit, 4 capita / unit
V-1.25 Multiple Family Residential, 1250 sf/unit, 2.8 capita / unit (rounded up)
OPEN
4 Variable use. See captia estimation by parcel.
5 Equivalent Dwelling Unit =400 gpd
S
S S
S S
S S
S S
S
S
S
S
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REVISION DATE DESCRIPTION MADE BY APPROVED
REVIEWED:DESIGNED BY:
DRAWN BY:
CHECKED BY:
SHEET NO.
OF SHTS
JUNE 2026
xx
COUNTY OF HAWAII
DEPARTMENT OF ENVIRONMENTAL MANAGEMENT, WASTEWATER DIVISION
ALI‘I DRIVE
SEWER LINE EXTENSION
TMK:(3) 7-7-010, 7-8-014
KAILUA-KONA, SOUTH KONA, HAWAI‘I
THIS WORK WAS PREPARED BY ME OR
UNDER MY SUPERVISION AND
CONSTRUCTION OF THIS PROJECT WILL
BE UNDER MY OBSERVATION.
EXPIRATION DATE OF
THE LICENSE
APRIL 30, 2028
PC
MM
LN
JOB NO.
BK JOB NO. 24A0108.00
NORTH
SCALE: 1"=80'
CONCEPTUAL SEWER PLAN
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SCALE IN FEET
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PROJECT: Alii Drive Sewer Extension JOB NO:24A108.00
CLIENT: County of Hawai‘i, DEM DATE:
SUBJECT: Opinion of Probable Cost - 0% Preliminary Design BY:PC/LN
FILE:https://us-partner-integrations.egnyte.com/msoffice/wopi/files/4efe577c-2b33-4816-ba1e-cdef8cab0597/WOPIServiceId_TP_EGNYTE_PLUS/WOPIUserId_-/[Alii-Drive-Sewer-Ext-OPC-0%-Options.xlsx]PRELIM OPC
Item
No.Altermate 1 Alternate 2 Alternate 3
Description
Unit Price Alternate 1 Total Alternate 2 Total Alternate 3 Total
CONSTRUCTION
MOBILIZATION
1 Additional Project survey
Lump Sum $$20,000 $20,000 $20,000
2 Geotechnical Engineering
Lump Sum $$75,000 $75,000 $75,000
2 Mobilization / Demobilization
Lump Sum $$375,000 $450,000 $200,000
3 BMPs and Erosion Control, In Place
Complete
Lump Sum $$250,000 $250,000 $250,000
4 Traffic Control
Lump Sum $$400,000 $400,000 $300,000
TOTAL FOR MOBILIZATION $1,120,000 1,195,000 845,000
DEMOLITION
5 1 0 0 Remove and dispose equipment, piping,
valves, fittings, and appurtenances in lift
station.
Lump Sum $120,000 $120,000 $0 $0
6 0 1 1 Remove and dispose existing 8-inch sewer
line and manhole
Lump Sum $50,000 $0 $50,000 $50,000
TOTAL FOR DEMOLITION $120,000 0 0
SEWER SYSTEM
7 3,000 3,000 0 Sewer Line, 8" PVC, In Place Complete
Per Lin. Ft.$100 $300,000 $300,000 $0
8 0 3,000 3,000 HDPE, 4", In Place Complete
Per Lin. Ft.$220 $0 $660,000 $660,000
30-Apr-26
Estimated Quantity
PROJECT: Alii Drive Sewer Extension JOB NO:24A108.00
CLIENT: County of Hawai‘i, DEM DATE:
SUBJECT: Opinion of Probable Cost - 0% Preliminary Design BY:PC/LN
FILE:https://us-partner-integrations.egnyte.com/msoffice/wopi/files/4efe577c-2b33-4816-ba1e-cdef8cab0597/WOPIServiceId_TP_EGNYTE_PLUS/WOPIUserId_-/[Alii-Drive-Sewer-Ext-OPC-0%-Options.xlsx]PRELIM OPC
Item
No.Altermate 1 Alternate 2 Alternate 3
Description
Unit Price Alternate 1 Total Alternate 2 Total Alternate 3 Total
30-Apr-26
Estimated Quantity
9 2,700 3,600 900 Trench excavation and backfill.
Per Cu. Yd.$500 $1,350,000 $1,800,000 $450,000
10 1 1 1 Connect to existing sewer manhole, in place
complete.
Each $10,000 $10,000 $10,000 $10,000
11 1 1 0 Lift Station, In Place Complete including
building, generator, SCADA, electrical, wet
well, pumps, etc.
Each $1,200,000 $800,000 $1,200,000 $0
12 11 12 1 Sewer manholes 5.0' to 9.99' deep, in place
complete.
Each $25,000 $275,000 $300,000 $25,000
13 3 4 0 Sewer manholes 10.0' to 14.99' deep, in
place complete.
Each $45,000 $135,000 $180,000 $0
14 0 1 1 Upsize existing sewer manhole and piping,
in place complete.
Lump Sum $65,000 $0 $65,000 $65,000
15 1 0 0 Sewer bypass
Lump Sum $100,000 $100,000 $0 $0
16 77 77 0 Sewer lateral up to P/L, in place complete.
Each $2,500 $192,500 $192,500 $0
19 0 0 77 Sewer lateral, 2" for LPSS
Each $1,500 $0 $0 $115,500
20 0 0 77 Sewer lateral valves and boxes
Each $500 $0 $0 $38,500
TOTAL FOR SEWER SYSTEM $3,162,500 4,707,500 1,364,000
MISCELLANEOUS
17 7,600 7,600 7,600 Asphalt concrete pavement and base
course, Mix 3, in place complete.
Per Sq. Yd.$120 $912,000 $912,000 $912,000
PROJECT: Alii Drive Sewer Extension JOB NO:24A108.00
CLIENT: County of Hawai‘i, DEM DATE:
SUBJECT: Opinion of Probable Cost - 0% Preliminary Design BY:PC/LN
FILE:https://us-partner-integrations.egnyte.com/msoffice/wopi/files/4efe577c-2b33-4816-ba1e-cdef8cab0597/WOPIServiceId_TP_EGNYTE_PLUS/WOPIUserId_-/[Alii-Drive-Sewer-Ext-OPC-0%-Options.xlsx]PRELIM OPC
Item
No.Altermate 1 Alternate 2 Alternate 3
Description
Unit Price Alternate 1 Total Alternate 2 Total Alternate 3 Total
30-Apr-26
Estimated Quantity
18 100 100 100 Concrete driveway apron replacement 6"
conc w/ 4" base, in place complete.
Per Sq. Yd.$300 $30,000 $30,000 $30,000
19 3,000 3,000 3,000 Striping
Per Lin. Ft.$10 $30,000 $30,000 $30,000
TOTAL FOR MISCELLANEOUS $972,000 972,000 972,000
Subtotal 5,374,500$ 6,874,500$ 3,181,000$
Contractor's Overhead, Profit, Insurance (25%)1,343,625$ 1,718,625$ 795,250$
Contingency (20%)1,074,900$ 1,374,900$ 636,200$
Tax (4.710%)253,139$ 323,789$ 149,825$
Total 8,046,164$ 10,291,814$ 4,762,275$
Total Construction Cost Say 8,100,000$ 10,300,000$ 4,800,000$