The Onsite Waste Treatment Systems (OWTS) Manual provides the regulations, procedural and technical details governing individual onsite wastewater treatment systems (also referred to as septic systems). State law mandates the State Water Resources Control Board (State Water Board) adopt standards for regulation of onsite waste treatment systems ( State Water Board OWTS Policy). The OWTS Manual complies with the State Water Resources Control Board OWTS Policy Tier 2 Local Area Management Program (LAMP) requirements.

Revised OWTS Manual – May 21, 2019

The proposed OWTS Manual that will be considered by the Board of Supervisors on May 21, 2019. It incorporates feedback from the public.

Full Version (PDF: 9.02 MB)

Single portfolio file.

Revised Sections (Accessible)

Alternate version divided into sections. All documents are in PDF format and fewer than 200 kB in size unless otherwise noted.

• OWTS Cover and Table of Contents
• Section 1 – General
• Section 2 – Sewer Connection Required
• Section 3 – Acronyms and Definitions
• Section 4 – Criteria for All OWTS
• Section 5 – Abatements, Abandonments and Repairs of Failing Systems
• Section 6 – Requirements for Approval of Building Permits
• Section 7 – Site Evaluation Methods and Investigation Requirements (Size: 393 kB)
• Section 8 – Criteria for OWTS Components (Size: 558 kB)
• Section 9 – Criteria for Standard OWTS
• Section 10 – Criteria for Water Reuse
• Section 11 – Criteria for Commercial, Industrial, and Institutional OWTS
• Section 12 – Non-Standard Experimental and Alternative OWTS Approval Process
• Section 13 – Non-Standard Experimental and Alternative OWTS Standards (Size: 2.57 MB)
• Section 14 – Non-Standard and/or Commercial OWTS Operational Permit and Monitoring
• Section 15 – Vesting Certificates
• Section 16 – Subdivisions and Lot Line Adjustment Requirements
• Section 17 – Variance Requirements
• Section 18 – Variance Prohibition and Special Standards Areas (Size: 3.35 MB)
• Section 19 – Dispute Resolution
• Section 20 – Tier 3 Treatment, Monitoring, Inspection and Sampling for Supplement Treatment Units
• Section 21 – Waterless Toilets
• Appendix A

August 31, 2018 Version

The previously proposed OWTS Manual dated August 31, 2018 incorporates feedback from the public and Board of Supervisors at the May 22, 2018 Board meeting and subsequent meetings with the Board of Supervisors Ad Hoc Committee.

Previous Version

Current OWTS Manual – September 22, 2016

The OWTS Manual that is currently in effect and will be replaced.

Current Manual (PDF: 9.7 MB)

Community Input

Read public comments and feedback on the OWTS Manual along with staff responses.

Community Meetings

The County of Sonoma is updating County regulations for septic systems in order to meet state mandated policy that protects water quality and public health. Permit Sonoma invited the public to attend community meetings to share feedback on the proposed Onsite Wastewater Treatment System (OWTS) Manual. The community meetings were held in September and October 2018.

View Meeting Details and Materials

• February 2018: Permit Sonoma drafted the proposed revision of the OWTS Manual to meet State requirements, a subcommittee of the Land Use Advisory Panel reviewed the revisions.
• February 22, 2018: Official public comment started on the publicly released Revised Manual.
• March 30, 2018: Permit Sonoma hosted a public workshop to discuss the revised OWTS Manual.
• May 22, 2018: Sonoma County Board of Supervisors received an informational only update regarding proposed OWTS Manual. After community testimony about potential regulatory and financial burdens resulting from the proposed manual, the Board postponed acceptance of the draft for six months so Board Members and staff can further engage the community and provide revisions to the Board by November 2018.
• June 2018 - August 2018: Permit Sonoma and Board of Supervisors OWTS Ad Hoc Committee meet to discuss potential revisions. Permit Sonoma prepares proposed revision and educational materials including flowcharts and frequently asked questions.
• August 31, 2018: Public release of Proposed OWTS Manual, which incorporates feedback from public and OWTS Ad Hoc Committee. Significant changes to the manual since the February 2018 version include updated septic system evaluation regulations for building permits, expanded list of variances, and elaborates on the criteria and process to enroll alternative and experimental systems.
• August 2018 - October 2018: Public feedback on proposed OWTS Manual via online survey and 5 community meetings.
• May 2019: Board of Supervisors considers acceptance of proposed OWTS Manual.

The main differences from the County’s current septic system regulations in the proposed manual include:

• Permit Types. There are three types of permits: new, replacement and repair. New OWTS serve undeveloped properties. Replacement OWTS are for tank replacements and/or dispersal system replacements for developed sites (previously known as a voluntary repair). Repair OWTS allow for the relatively minor work: distribution box, valves, etc.
• Classifications. Class I, II and III classifications would be replaced with references to either Code Compliant or Legal Non-Conforming systems
• Code Compliant OWTS means a system that is in conformance with this OWTS Manual, or meets the intent of the standards by proposing mitigation measures that are equal to the standards.  A Code Complaint OWTS can be new or existing. 
• Variances. Code compliant does not mean that you need a new system or that you meet each and every standard. The County allows variances from the standards provided sufficient mitigation is provided. The proposed regulations allow more variance issues and more mitigation measures.
• Voluntary Repairs. Previous voluntary repairs regulations would be eliminated. Typical voluntary repairs include replacing dispersal systems. A new or replacement dispersal system must meet a two (2) foot separation to groundwater, have adequate soil type and depth, and be designed by an appropriately licensed professional defined as qualified consultants in the State Business and Professions Code.
• Building Permits. Prior regulations required a septic evaluation for most building permits. The proposed regulations require a septic system evaluation or possibly a new code compliant system only when the project increases wastewater flow and/or strength to the existing system. The proposed regulations also evaluate the location of the proposed building/construction relative to the septic system and reserve area. The intent is to avoid physical impacts to the septic system. In certain cases, reserve replacement areas will be evaluated or required.
• Alternative & Experimental Systems. The proposed regulations expand the list of currently approved and conditionally acceptable experimental and/or alternative systems and elaborates on the criteria and process to enroll various innovative technology/systems into either the experimental system program and/or the alternative system program.
• Financial Hardship. The proposed regulations create financial hardship provisions, that if met, would exempt a client from the standards.  The septic system would need to comply with the standards to maximum extent feasible.
• Waiver. The North Coast Regional Water Quality Control Board adopted a revised Waiver of Waste Discharge Requirements that now includes OWTS that cannot meet the two (2) foot separation to groundwater. If the system cannot meet the two (2) foot separation standard, the client would have to apply to the NCRWQCB for their wavier.  Local agencies cannot waive this standard according to the State’s OWTS Policy, but will act as the technical lead for review.