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Septic Systems

In areas where public sewer is not available, homeowners must have septic systems installed on their property that will treat wastewater coming from their home.

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Sanitation Sewer Information
A sanitary sewer system collects and transports waste from indoor plumbing fixtures to treatment plants.

End of Extended COVID Permit Expiration Date

In order to support the difficulties the COVID-19 pandemic brought to the community, Permit Sonoma offered customers a two-year extension above and beyond the regular timelines for various ministerial applications and permits. The conditions attributing to the local emergency no longer exist and the Board of Supervisors is rescinding the local emergency as of May 16, 2023. As such, the policy extending the expiration dates will sunset effective May 17, 2023.

This change does not affect permits that have already been extended. All applications received beginning May 17, 2023 will be valid for one year, and the COVID-19 extension will not be applied.

View Affected Permit Types

Types of Septic Systems

There are two types of septic systems:

Standard Onsite Wastewater Treatment System (OWTS)

A type of OWTS consisting of a septic tank for primary treatment of sewage, followed by a system of drainfield trenches for subsurface dispersal of effluent into the soil. A standard OWTS may utilize gravity flow or a pump system to convey effluent from the septic tank to the drainfield.

Non-standard Onsite Wastewater Treatment System

A type of OWTS that utilizes a method of wastewater treatment that may or may not include a conventional septic tank and/or method of wastewater dispersal other than a conventional drainfield for the purpose of producing an equal to or greater quality wastewater effluent and improved performance of and siting for effluent dispersal than a standard OWTS. There are two types of non-standard systems. There are two types of non-standard OWTS:

  • Alternative OWTS: an approved non-standard OWTS that has demonstrated in the non-standard Experimental phase to function in such a manner as to protect water quality, preclude health hazards and nuisance conditions and capable of producing an equal to or greater quality wastewater effluent and improved performance of and siting for effluent dispersal than a standard OWTS. Examples of these are pretreatment units, mound OWTS, shallow trench pressure distribution OWTS, at-grade OWTS, shallow in ground OWTS, bottomless sand filter OWTS, and subsurface drip dispersal OWTS.
  • Experimental OWTS: a non-standard OWTS deemed conditionally acceptable by the Regional Water Quality Control Board, subject to increased performance monitoring and evaluation, prior to acceptance as an approved non-standard Alternative OWTS. Examples of these are bottomless sand filter OWTS and gravel-less pressurized dispersal channels.

Cottage Foods Septic Requirements

Cottage Food Operation Permit Requirements for Operators on Septic Systems

This guidance document is for Cottage Food Operations that are connected to an onsite septic system for liquid waste disposal, verses a county or city sewer system.

Cottage Food Operation (CFO) is governed under the California Homemade Food Act and it allows for certain types of food to be prepared and sold from a home kitchen operated food facility.   Governor Brown signed the California Homemade Food Act into law on September 21, 2012.

View the Requirements

Site Evaluations, Testing, and Monitoring

Properties with septic systems may need the following evaluations, testing, and monitoring activities.

Site Evaluation

Before you apply for a septic permit you will need a soils profile evaluation and you may need percolation and groundwater testing. 

  • Soils Profile Evaluation: Soil profile holes for the Preliminary Site Survey Soil Profile Evaluation are for the purpose of observing soil structures, texture, formations; the presence of seasonal groundwater; impervious rock formations, etc. Profiles are essential in the evaluation of any parcel for soil suitability for private sewage dispersal systems.
  • Percolation Test: A test conducted to determine the permeability or percolation quality of the soil in an area proposed for sewage dispersal.
  • Wet Weather Percolation & Groundwater Testing: Required when a new or replacement septic system is installed, as well as if the septic system is located in a basin area with slopes of 0% to 5% or is in a defined geographic area that has received 50% of seasonal rainfall.

Operational Permit (OPR) and Monitoring Program – Non-Standard Septic Systems

Owners with non-standard septic systems are required to participate in the County’s operational permit (OPR) monitoring program.

Recommended Septic Maintenance and Reminders

The following activities are recommended to properly maintain your septic system: 

  • Clean Sump filter annually.
  • Pump septic tank every 3-5 years depending on use.
  • Purge and balance system annually by a C42 or Engineering Contractor familiar with these systems.
  • Switch diversion valve (if you have one) annually, or as specified on approved septic plans.
  • For those with pre-treatment units requiring sampling for analysis, see #7 on supplemental agreement, provide results to our office once per year for at least 2 years. Samples may be taken from sump tank.
  • Keep expansion areas unencumbered.

Resources for maintaining septic systems and vegetative cover: