Glossary

Advanced Protection Management Program (APMP): A Regional Water Board approved local program for areas near impaired surface waters. Where an APMP exists, it governs Tier 3 systems in place of the Policy's default Tier 3 requirements.

ADU: Accessory Dwelling Unit. Adding one to a property served by a septic system requires approval from the local health officer under Government Code 65852.2(a)(1)(D)(ix). Whether the county can approve it locally depends on which OWTS tier applies. A definition for ADUs was added to the OWTS Policy in the April 2023 amendment.

AB 885: The Assembly Bill that amended California Water Code section 13290, requiring the State Water Board to develop statewide standards for permitting and operating onsite wastewater treatment systems. The OWTS Policy is the result.

Attachment 2: The list of impaired water bodies in the OWTS Policy for which septic discharges are likely to contribute pathogens or nitrogen. A system within 600 feet of a listed water body falls into Tier 3. The list was amended in April 2023, with some water bodies removed.

CEDEN: California Environmental Data Exchange Network. Local agencies with a LAMP must submit surface water monitoring data here annually by February 1.

Conditional Waiver: The waiver of waste discharge requirements built into the OWTS Policy for systems that comply with it. By law it expires every five years, which is why the Policy has been renewed in 2018 and 2023, with the next renewal due to take effect May 13, 2028.

CWSRF: Clean Water State Revolving Fund. A financing source some California counties use to fund local septic repair programs. A definition was added to the OWTS Policy in the April 2023 amendment.

Domestic Wastewater: Wastewater from residential and comparable sources. A formal definition was added to the OWTS Policy in the April 2023 amendment.

GeoTracker: The State Water Board database where local agencies with a LAMP must submit groundwater monitoring data, in electronic deliverable format.

LAMP: Local Agency Management Program. A county or city program approved by its Regional Water Board that governs new and replacement systems locally. Under Section 9, a LAMP's siting and design standards may differ from the statewide Tier 1 defaults, in either direction.

Leach Field: The subsurface area where effluent disperses into soil for final treatment. Also called a drain field or disposal field.

Local Agency: The county environmental health department, or in some cases a city, that issues OWTS permits. Roughly 66 local agencies operate across California's nine regional water board areas.

OWTS: Onsite Wastewater Treatment System. California's regulatory term for what most people call a septic system. There are an estimated 1.2 million in the state.

OWTS Policy: The Water Quality Control Policy for Siting, Design, Operation and Maintenance of Onsite Wastewater Treatment Systems. Adopted June 19, 2012 under Resolution 2012-0032, effective May 13, 2013, amended April 17, 2018 and April 18, 2023.

Regional Water Board: One of nine Regional Water Quality Control Boards that oversee local agencies, approve LAMPs, and act as the permitting authority where a proposal falls outside the local program.

Report of Waste Discharge: The application a system owner may need to file for coverage under Waste Discharge Requirements, typically where projected flow exceeds 10,000 gpd or the system receives high-strength wastewater.

Seepage Pit: A deep excavation used for effluent disposal in place of a conventional leach field. Still used in parts of California, but prohibited in some counties including Mono County.

Supplemental Treatment: Additional treatment beyond a conventional tank and leach field, which may be required for Tier 3 systems near impaired water bodies. The single biggest cost variable in California septic.

Tier 0: Existing properly functioning systems needing no corrective action, under Section 6. Maximum flow 10,000 gpd. Does not apply to systems near an impaired water body subject to a TMDL, covered by a local special provision, or within 600 feet of a listed water body.

Tier 1: New or replacement systems meeting the Policy's conservative statewide siting and design standards, under Sections 7 and 8. Applies wherever no LAMP has been approved. Maximum flow 3,500 gpd, the lowest ceiling of any tier.

Tier 2: New or replacement systems permitted under an approved LAMP, under Section 9. Standards may differ from Tier 1. Maximum flow 10,000 gpd.

Tier 3: Systems near impaired surface waters subject to a TMDL implementation plan, a LAMP special provision, or within 600 feet of a listed water body, under Section 10. Supplemental treatment may apply. Maximum flow 10,000 gpd.

Tier 4: Systems requiring corrective action, under Section 11. Failure is indicated by surfacing effluent, wastewater backing up in plumbing fixtures, structural failure of a component or pipe, or significant groundwater or surface water degradation.

TMDL: Total Maximum Daily Load. A pollutant limit set for an impaired water body. Where a TMDL implementation plan covers an area, systems there may fall into Tier 3.

WDR: Waste Discharge Requirements. The permit framework that applies to discharges falling outside the OWTS Policy's conditional waiver, including large systems and certain commercial food service operations.