The Governing Framework

Hawaii regulates onsite wastewater under:

• HAR Title 11, Chapter 62 — Wastewater Systems. The substantive rule covering public wastewater systems and Individual Wastewater Systems (IWS).
• HAR Title 11, Chapter 62, Subchapter 3 — Individual Wastewater Systems specific requirements.
• Act 125 (2017) — Session Laws of Hawaii. Requires conversion of all cesspools in Hawaii by 2050 with accelerated priority-based deadlines.
• Hawaii Department of Health (DOH), Wastewater Branch — state-level administrator. (808) 586-4400.
• County integrated wastewater management plans — particularly active at Hawaii County DEM (Department of Environmental Management).

Act 125 — The Cesspool Conversion Mandate

Hawaii Act 125 is one of the most consequential onsite wastewater laws in the United States. Passed in 2017, it:

• Prohibits installation of new cesspools. Effective at passage. New construction must use approved alternatives.
• Mandates conversion of ALL existing cesspools by January 1, 2050. No exceptions for continued cesspool operation past that date.
• Establishes priority-based accelerated deadlines. Using the University of Hawaii's 2022 hazard assessment and prioritization tool, cesspools are tiered by environmental hazard. High-priority cesspools must be converted by 2030; medium-priority by 2035; all others by 2050.

Approved alternatives include conventional septic tanks with absorption system, aerobic treatment units (ATUs), and advanced reuse systems. A polyethylene septic tank conforming to HAR Chapter 62 standards is a straightforward cesspool-replacement option for many properties.

Individual Wastewater Systems (IWS) — HAR 11-62 Subchapter 3

For properties beyond public wastewater service, Individual Wastewater Systems are permitted under Subchapter 3. Key constraints:

• Current rules allow up to two (2) dwelling units per IWS (may or may not be in same building)
• IWS deployed in remote areas and areas of low population density
• Design and construction per HAR 11-62 requirements — tank capacity, setbacks, absorption system
• DOH Wastewater Branch oversight and permitting

When replacing a cesspool with an IWS (typically septic tank + absorption), the replacement system must comply with current HAR 11-62 standards. Older non-conforming systems cannot simply be "upgraded in place" without bringing the full configuration into compliance.

Cesspool Priority Levels — UH 2022 Assessment

The University of Hawaii's 2022 cesspool hazard assessment and prioritization tool tiered Hawaii's cesspools based on:

• Proximity to drinking-water sources (groundwater aquifers and wells)
• Proximity to recreational waters and coral-reef ecosystems
• Soil type and infiltration characteristics
• Depth to water table and bedrock
• Population density of surrounding area

Homeowners can check their cesspool priority designation through DOH or UH resources. Priority 1 and 2 deadlines are approaching — 2030 is closer than it seems.

Island-Specific Considerations

• Oahu (Honolulu County): Most densely populated. Large portions on central sewer. Remaining cesspools concentrated in older neighborhoods and windward/North Shore communities.
• Hawaii Island (Big Island, Hawaii County): The highest cesspool count of any island. Active Integrated Wastewater Management Plan at Hawaii County DEM. Volcanic terrain complicates conversion engineering.
• Maui County (Maui, Molokai, Lanai): Extensive rural cesspool inventory. Destination Maui and other local commentary highlight community concern about conversion cost.
• Kauai County: Mix of coastal and mountain installations. Coral-reef protection a high priority.
• Niihau: Limited public utility infrastructure; onsite systems are the norm.

Conversion Engineering Considerations

Converting a cesspool to a compliant septic + absorption system on a Hawaii parcel involves:

• Site evaluation of soil, slope, proximity to wells and property boundaries
• Septic tank installation (polyethylene tanks commonly used for ease of transport to island sites)
• Absorption system design compatible with volcanic soil permeability
• Possible need for alternative systems (ATU, media filter) on constrained parcels
• Coordination with county DEM integrated wastewater plans
• DOH Wastewater Branch permit

Conversion costs vary widely by site — budgeting $15,000–$50,000+ is realistic for most residential conversions, with higher costs on difficult sites or where alternative treatment is required.

Frequently Asked Questions

What happens if I don't convert my cesspool by the deadline?

Act 125 requires conversion. Non-compliance exposes property owners to enforcement action by DOH and the state. Practical considerations also include property-sale implications — buyers increasingly scrutinize cesspool status, and a non-compliant system can complicate transactions even before the final 2050 deadline. Start planning early for priority-1 and priority-2 cesspools.

How do I find my cesspool's priority level?

The University of Hawaii 2022 hazard assessment identifies priority levels. DOH Wastewater Branch can provide information about your specific property. Start with DOH at (808) 586-4400 or the Wastewater Branch online resources.

Are there financial assistance programs?

Yes, various programs have been established to help homeowners with cesspool conversion costs. Programs evolve — check current availability through DOH, County Departments of Environmental Management, and wastewater clean-water advocacy organizations.

Are polyethylene tanks accepted in Hawaii?

Yes, when meeting IAPMO/NSF listings and HAR 11-62 construction requirements. Rotomolded polyethylene tanks are often preferred for Hawaii due to ease of transport to island sites and corrosion resistance in coastal environments. Major OEM tanks from Norwesco, Snyder, and others are commonly approved.

What's the two-dwelling-unit limit for IWS?

HAR 11-62 Subchapter 3 limits IWS to two dwelling units. For three-plus dwelling properties, a larger wastewater treatment system is required (and may fall under different permitting tracks). Plan for this constraint at property development.

Do I need to convert immediately if I'm selling my property?

Legal obligation follows the ownership transfer. Buyers increasingly require conversion or price adjustment reflecting conversion cost. Disclosure rules typically require identifying cesspool presence in sale transactions. Consult a Hawaii real-estate attorney for specifics of your situation.

Source Citations

• Hawaii DOH Wastewater Branch Chapter 11-62
• HAR Title 11 Chapter 62 Wastewater Systems
• HAR 11-62 Subchapter 3 Individual Wastewater Systems
• EPA Cesspools in Hawaii
• Wastewater Alternatives and Innovations (WAI) FAQs
• Hawaii County Integrated Wastewater Management Plan
• HAR 11-62 Ramseyer Version (DOH)

Agricultural Tank Regulations — HDOA & HDOH

The Hawaii Department of Agriculture (HDOA) and the Hawaii Department of Health (HDOH) share agricultural-tank oversight under the Hawaii Revised Statutes (HRS) and the Hawaii Administrative Rules (HAR):

• HAR 4-66 — HDOA Pesticide rules; applicator licensing, restricted-use pesticide (RUP) recordkeeping, bulk storage, repackaging.
• HRS Chapter 149A — Hawaii Pesticide Law (statutory authority).
• HAR 4-62 — HDOA Commercial Fertilizer Materials registration and labeling.
• HAR 11-23 and HAR 11-62 — HDOH Safe Drinking Water and Wastewater rules that overlay ag water supply, irrigation reservoir, and manure/septage handling.

Hawaii agriculture centers on seed-corn and crop research in Kauai (Kekaha, Mana) and Oahu (Kunia, Waipio), Big Island macadamia (Ka'u, Kona, Hamakua), Big Island and Kona coffee, Maui and Big Island specialty crops (protea, vegetables, tropical fruit), cattle on the Big Island (Parker Ranch, Kahua), and aquaculture at Natural Energy Laboratory of Hawaii Authority (NELHA) and similar sites. The defining Hawaii constraint is sole-source aquifer dependence: virtually all Hawaii drinking water comes from a short list of federally designated sole-source aquifers (Pearl Harbor, Central Oahu, Windward Oahu, and island-by-island analogs), which forces tank siting and containment scrutiny well above continental norms. Ag retailers handling bulk liquid fertilizer and pesticides build secondary containment to 110% of the largest tank with impermeable liners, loading-pad spill recovery, and HDOH-aligned spill-response plans; siting must also contend with salt-spray corrosion anywhere within several miles of the coast, which on islands means nearly every ag parcel. Salt-spray corrosion considerations push metal tanks toward heavy hot-dip galvanizing, epoxy or polyurethane topcoats, 316L stainless fittings, or polyethylene construction to avoid accelerated fastener and wall corrosion.

Oil & Gas Storage — Petroleum UST Path

Hawaii has no oil or gas production; all petroleum is imported by tanker to Honolulu Harbor, Kalaeloa (Barbers Point), and neighbor-island terminals, then distributed by inter-island barge and truck. Petroleum storage is governed through:

• HAR 11-280.1 — HDOH Safe Drinking Water Branch UST rules: design, installation, corrosion protection, spill/overfill, release detection, operator training, closure, financial responsibility.
• HAR 11-281 — HDOH Aboveground Storage Tank rules; regulated AST framework covering design, containment, and release response.
• HRS Chapter 342L — Underground Storage Tanks statutory authority.
• NFPA 30 / 30A — adopted through State Fire Council and county fire codes for flammable and combustible liquids.
• Red Hill Bulk Fuel Storage Facility — the Navy bulk-fuel complex above the Pearl Harbor Aquifer, subject to federal (Navy, EPA Region 9, DoD) and state HDOH enforcement; the 2021-2022 Red Hill releases reshaped Hawaii's regulatory focus on tank integrity above sole-source aquifers and drove the HDOH administrative-order defueling process.

Honolulu refining (Kalaeloa) and fuel terminals (Par Hawaii, Island Energy Services, Aloha Petroleum) hold the state's primary bulk storage. Offshore federal OCS is effectively absent for oil and gas given the Pacific tectonic setting.

Septic System Sizing — HAR 11-62

HDOH regulates on-site wastewater under HAR 11-62 (Wastewater Systems). Residential design flow is 200 gpd per bedroom — notably higher than the 150 gpd/bedroom continental norm, reflecting Hawaii water-use patterns, irrigation return flows, and aquifer-protection conservatism:

Hawaii septic design carries several unique constraints. Cesspools — single-pit, non-treating disposal systems — were banned for new construction in 2016 and are mandated for conversion to septic or sewer by 2050 under Act 125 (2017). The conversion program is one of the most aggressive on-site-wastewater upgrade mandates in the country, affecting an estimated 83,000 cesspools statewide concentrated in Hawaii County, Maui County, and rural Oahu. Conservation District siting (HAR 13-5) imposes additional permitting and setback requirements on any parcel classified Conservation (roughly 48% of state lands), which includes many rural residential properties and forces advanced-treatment systems, minimal footprint, and careful siting relative to streams, gulches, and shoreline. Ocean-front setback under county Shoreline Management Area rules and the Special Management Area (HRS Chapter 205A) requires septic tanks and dispersal fields to be set back from the shoreline and elevated above tidal and wave inundation; on vulnerable parcels, elevated tanks with anti-flotation ballast, reinforced risers, and pressure-dosed dispersal are the rule. Soils range from deep weathered volcanic on Kauai and Oahu (excellent perc) to young lava on the Big Island (perc ranges from near-infinite on vesicular pahoehoe to very slow on weathered aa and cinder). Perc tests are mandatory.

Chemical Storage, Salt-Spray Corrosion & Spill Reporting

Federal SPCC (40 CFR 112) applies at 1,320 gallons aggregate aboveground oil. Hawaii layers on aquifer-protection and coastal-zone frameworks that exceed continental practice:

• HAR 11-451 — HDOH Hazard Evaluation and Emergency Response (HEER) Office; the state cleanup program analog to federal CERCLA for hazardous-substance releases.
• HRS Chapter 128D — Environmental Response Law; strict, joint-and-several, retroactive liability for hazardous-substance releases.
• HAR 11-451-6 — release-reporting requirements to HDOH HEER; spills above reportable quantities trigger immediate notification.
• NFPA 30 / 30A — adopted through State Fire Council and county fire codes for flammable and combustible liquids.
• Salt-spray corrosion — not a single rule but a service-condition reality: per ISO 9223 atmospheric corrosivity classification, Hawaii coastal parcels routinely exceed C4 (high) and can reach C5 (very high) within a few hundred meters of the shoreline. Steel tanks require hot-dip galvanizing plus multi-coat epoxy or polyurethane, stainless or polymer-lined fittings, and inspection cycles tightened beyond continental SPCC expectations. Polyethylene storage is often preferred for chemical service at coastal sites because it eliminates galvanic and atmospheric corrosion.

Report federal-RQ releases to the National Response Center at 1-800-424-8802; report state releases to HDOH HEER at 808-586-4249 (Oahu) or neighbor-island HEER numbers published on the HDOH website.

Permit Pathways at a Glance

• Residential septic: HDOH Wastewater Branch under HAR 11-62.
• Cesspool conversion: HDOH under Act 125 / HRS Chapter 342D; 2050 deadline.
• Pesticide applicator license: HDOA under HAR 4-66.
• Fertilizer registration: HDOA under HAR 4-62.
• Petroleum UST: HDOH Safe Drinking Water Branch under HAR 11-280.1.
• Petroleum/chemical AST: HDOH under HAR 11-281 + federal SPCC + NFPA 30/30A.
• Conservation District / SMA: DLNR and county planning under HAR 13-5 and HRS 205A.
• Release investigation / cleanup: HDOH HEER under HAR 11-451.

Current fees change; verify with HDOH, HDOA, DLNR, or State Fire Council before budgeting.

More Hawaii FAQs

What is the cesspool conversion mandate and when does it affect me?

Act 125 (2017), codified at HRS Chapter 342D, bans new cesspool construction and requires conversion of all existing cesspools to septic, aerobic treatment, or sewer by 2050. HDOH administers the program with county cooperation; tax credits are available for qualifying early conversions. Approximately 83,000 cesspools remain statewide, concentrated in Hawaii County, Maui County, and rural Oahu. Any property transfer, remodel, or on-site wastewater work triggers cesspool-conversion scrutiny; budget tank, pump chamber, and dispersal-field replacement on any parcel with a legacy cesspool.

How does Conservation District status affect my tank project?

Under HAR 13-5, roughly 48% of Hawaii lands are classified Conservation District and require DLNR Board of Land and Natural Resources (BLNR) approval for most uses, including on-site wastewater and bulk-storage tanks. Conservation subzones (Protective, Limited, Resource, General, Special) set progressively more restrictive use regimes. Projects in Conservation District typically require a Conservation District Use Permit (CDUP) or Conservation District Use Application (CDUA) before any grading or tank installation. Timelines run months.

What is the Special Management Area and how does it overlay the coast?

HRS Chapter 205A established the Special Management Area (SMA) along all shoreline corridors, administered by the four counties. SMA permits are required for most construction, grading, and bulk-storage installation within the SMA; shoreline setback determinations (county-specific, typically 40-150 feet from the certified shoreline) govern where tanks, dispersal fields, and secondary containment can sit. Elevated tanks with anti-flotation ballast are standard on vulnerable parcels.

Why do metal tanks fail faster on Hawaii coasts?

Hawaii coastal atmospheric corrosivity routinely exceeds ISO 9223 Class C4 (high) and can reach C5 (very high) within a few hundred meters of breaking surf. Uncoated or single-coat steel can exhibit 10-20x continental corrosion rates; fasteners, gauges, vents, and fittings corrode first and fail first. Best practice is hot-dip galvanizing plus two-coat epoxy/polyurethane, stainless or polymer-lined hardware, polyethylene construction where service chemistry allows, and inspection cycles tightened relative to federal SPCC expectations.

What happened at Red Hill and how does it affect my permit?

The Navy Red Hill Bulk Fuel Storage Facility sits above the Pearl Harbor sole-source aquifer. Fuel releases in 2021-2022 contaminated Navy drinking-water wells and catalyzed HDOH administrative orders, federal defueling, and closure. The regulatory aftermath has tightened HDOH and EPA scrutiny on any above-aquifer tank storage statewide; expect more conservative siting, double-wall construction, interstitial monitoring, and enhanced release-detection requirements on any project near or above mapped sole-source aquifers.

How fast must I report a release in Hawaii?

Under HAR 11-451 any release of a hazardous substance above reportable quantity to soil, water, or air must be reported to HDOH HEER immediately; petroleum releases under HAR 11-280.1 and 11-281 also require prompt reporting. Federal-RQ releases also go to NRC at 1-800-424-8802. HDOH HEER 24-hour is 808-586-4249 (Oahu); neighbor-island contacts are published on the HDOH website. Hawaii's HRS 128D liability is strict, joint-and-several, and retroactive.