Onsite Wastewater Treatment Systems

Policy Implementation Program

To request a copy of documents listed on this page, please contact Chad Neptune at Chad.Neptune@waterboards.ca.gov


California has more than 1.2 million onsite wastewater treatment systems (OWTS). Over 40% of these are in the Central Valley. OWTS are typically domestic systems in areas without centralized sanitary sewers. Most do not pose a significant threat to human health and water quality. However, poorly sited, designed, and maintained OWTS can impact shallow groundwater, primarily with nitrates and pathogens. Historically, pursuant to Central Valley Water Board Resolution 73-129 local agencies solely regulated most OWTS. The Central Valley Water Board issued Waste Discharge Requirements for some large subdivisions and in cases of pollution or nuisance from multiple OWTS issued Prohibition Orders.

Due to statewide public concerns about OWTS, in 2000 Governor Gray Davis codified California Water Code §13290 et. seq., a modified form of Assembly Bill 885. These sections directed the State Water Resources Control Board (State Board) to adopt standards or regulations for OWTS by 1 January 2004. In 2005, State Board released draft standards, but opposition from the regulated community prevented their adoption. Environmental activist groups sued State Board for failure to act. Therefore, on 19 June 2012 State Board adopted Resolution No. 2012-0032, which includes the Water Quality Control Policy for Siting, Design, Operation and Maintenance of Onsite Wastewater Treatment Systems (OWTS Policy). On 13 May 2013, the OWTS Policy became effective. On 27 March 2014, the Central Valley Water Board adopted related Resolution R5-2014-0036 to amend the Water Quality Control Plans for the Sacramento, San Joaquin, and Tulare Lake Basins. On 9 September 2014, State Board Resolution 2014-0046 approved the amendments.

The goal of the OWTS Policy is to correct and prevent system failures due to poor siting and design, and excessive OWTS densities. The OWTS Policy recognizes that local agencies, typically county health departments, have greatest regulatory expertise; therefore they remain as leads. However, local agencies historically focused on public health. The OWTS Policy adds focus on water quality protection with a risk-based approach for new, replacement, and failing OWTS.

Four risk tiers require increasing Regional Board oversight of local agencies: Tier 0 covers properly functioning, existing OWTS with up to 10,000 gallons per day of projected flow. These require no changes in local codes and ordinances. Tier 1 covers low-risk new and replacement OWTS with up to 3,500 gallons per day of projected flow. Tier 1 has conservative, largely prescriptive default standards. Tier 2 covers new and replacement OWTS with up to 10,000 gallons per day of projected flow that do not meet Tier 1 standards. For these OWTS, local agencies have the option to propose Local Agency Management Programs (LAMPs) for Regional Board approval.

Tier 2 LAMPs are the OWTS Policy’s key focus, with alternative standards overall protective as Tier 1 of human health and water quality. The Central Valley has 29 local agencies with Regional Board approved LAMPs. Pursuant to OWTS Policy §9.3.3, local agencies with approved LAMPs shall periodically submit Water Quality Assessment (WQA) Reports. With nitrogen and pathogen laboratory results from potentially relevant water supply wells and surface water bodies, WQA Reports assess the potential effect of OWTS on water quality. Reports are due every five years, on 1 February. In the Central Valley, the submittal date for the first WQA Report is 1 February 2023.

Tier 3 includes OWTS less than 600 feet from Clean Water Act 303(d) listed impaired water bodies for nitrates and pathogens. For these OWTS, LAMPs must include Advanced Protection Management Programs (APMPs). OWTS Policy Attachment 2. has two impaired water bodies in the Central Valley Region, Wolf and Woods Creeks. Based on current information, LAMPs for Nevada and Tuolumne Counties therefore include APMPs for pathogens.

Tier 4 covers failing OWTS and specifies minimum corrective actions. Major repairs due to inadequate effluent percolation, wastewater exfiltration to groundwater, or groundwater infiltration into a septic tank or dispersal system can restore an OWTS to Tiers 1, 2, or 3. Other repairs, e.g., to distribution boxes and broken pipe connections, can restore an OWTS to Tiers, 0,1, 2, or 3.

Pursuant to OWTS Policy §3.3, all local agencies, whether or not with an approved LAMP, shall submit annual spreadsheet format reports. Annual reports are due 1 February and should summarize; complaints about OWTS maintenance and operation and their resolutions (e.g., repairs); applications and registrations under California Health and Safety Code §117400 et seq. (septic tank cleaning program); and permits for new and replacement OWTS. Lake County, the Cities of Clovis and Fresno in Fresno County, and the City of Visalia in Tulare County regulate OWTS under Tier 1 and solely submit annual reports.

Program Information

Local Agency Management Programs (LAMPs)

Local Tier 2 standards, alternative to those in Tier 1 as described in the State Water Resources Control Board Water Quality Control Policy for Siting, Design, Operation, and Maintenance of Onsite Wastewater Treatment Systems (OWTS Policy), Sections 7, 8, and 9.

Basin Plan Amendments to Incorporate the OWTS Policy

(amends the Basin Plans to remove current septic tank guidelines and incorporate the OWTS Policy)

  • State Water Board Action: 9 September 2014

  • Central Valley Water Board Action: 27 March 2014 - The Central Valley Water Quality Control Board held a public hearing during its regular Board meeting and adopted amendments to the Basin Plans

Prohibition Orders

Central Valley Regional Water Quality Control Board Prohibitions for leaching systems, as listed in:
NOTE:  For Fresno and Tulare Counties, local moratoria prohibit new OWTS in the following areas:
  • Fresno County - Del Rio
  • Tulare County - Delft Colony, El Rancho, Lindcove, Poplar, Seville, Tonyville, Tooleville, Traver, Wells Tract, and Yettem

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