Skip to Content

Onsite Waste Treatment Systems (OWTS) Manual


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.

OWTS Manual Adoption

The Director of Permit Sonoma published the County of Sonoma’s Onsite Wastewater Treatment System Manual, version 6.0, dated May 21, 2019, pursuant to Sonoma County Code section 24-31.5. The comment period started on June 22, 2019, and ended July 5, 2019. The Director received and considered numerous comments. Revisions included fixing various typographical errors and cleanup language. The statutory requirements of Sonoma County Code section 24-31.5 have been satisfied.

As such, the Director hereby adopts the County of Sonoma’s Onsite Wastewater Treatment System Manual, version 7.0, dated August 15, 2019.

Proposed Revisions Onsite Wastewater Treatment System Manual

The County of Sonoma is pleased to release the latest draft of our Onsite Wastewater Treatment Systems (OWTS) Manual. We will be holding Zoom meetings the week of June 26-28, 2024, to receive public comments. 

Meeting Dates:

A summary of why the OWTS Manual is being revised, the implications to existing and new development, how this manual interacts with the Total Maximum Daily Load (TMDLs) in the County, and an overview of the changes on the OWTS Revisions can be found on our Regulations Website. We also provide links to comments and responses received from the OWTS design community as part of developing the proposed revisions to the OWTS Manual.

Staff will be presenting a Local Agency Management Program and the revised OWTS Manual to the Board of Supervisors on July 16, 2024.

Draft OWTS Manual:

Staff are seeking authorization to submit these two documents to the North Coast RWB as the County’s application for a local OWTS program. This is being done pursuant to the State’s OWTS Policy.

OWTS Manual

The OWTS Manual and associated documents are presented below.

Entire Manual in a Single Document

Please note you must have Adobe Flash installed on your computer to view this portfolio. Alternatively, you can scroll down to view the manual as individual sections below.

OWTS Portfolio (PDF: 8.99 MB) (Adobe Flash required)

Manual Broken Into Sections / Accessible Version

Each document below is in PDF format and is under 550 kB unless otherwise noted.