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Onsite Wastewater Treatment Systems (OWTS) Frequently Asked Questions

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Find answers to frequently asked questions (FAQS) related to the County’s septic system program and proposed updates to County septic regulations. If you have a question that you don’t see listed on this page, please let us know.

OWTS topics on this page:


What does “OWTS” stand for?

"OWTS" stands for Onsite Wastewater Treatment Systems which are commonly referred to as septic systems.

How do I know if I have an OWTS (septic system)?

If you are not paying a sewer bill then you likely have an OWTS. If you have a septic tank then you likely have an OWTS. If you pay a sewage hauler then you likely have an OWTS.

What is a standard OWTS?

A standard OWTS includes a septic tank and leach line or dispersal system.

What is an experimental OWTS?

Experimental OWTS are non-standard OWTS that are conditionally acceptable subject to increased performance monitoring and evaluation prior to acceptance as an approved alternative OWTS.

What is an alternative OWTS and which alternative systems are approved?

Alternative OWTS are approved non-standard OWTS that have demonstrated in the non-standard Experimental phase to function reliably in a variety of conditions and which are protective of water quality and environmental health. Sonoma County has approved and installed numerous types of alternative OWTS. See list of alternative and experimental systems.

Where do Composting Toilets fit in?

Composting toilets are being evaluated on the technical side as well as for draft regulations. There is one permitted system in the County which is currently in operation and is being monitored.

Conceptually, the County is considering treating composting toilets as an allowed system provided the solids are hauled offsite for proper disposal by a licensed hauler. A septic system would still be required due to the other waste streams (gray water and kitchen waste) generated in the single family dwelling. A composting toilet may reduce the size of a normal septic system, but not eliminate that need. Other types of experimental and alternative systems are being evaluated as well.

New Regulations

What are the changes to California OWTS policy?

State Assembly Bill 885, signed into law in 2000, requires counties to adopt new regulations for the permitting and operation of OWTS. In response to the state law, the State Water Resources Control Board adopted their OWTS policy in 2012. You can view this policy online.

Why did the State Water Resources Board adopt a statewide OWTS Policy?

To be in compliance with state law. The goal is to reduce the impact on the environment and public health and to have a state-wide system to do so.

What is the County’s Local Area Management Program (LAMP)?

LAMP comes from the State’s OWTS Policy and stands for Local Area Management Program. Counties were required to submit a LAMP to the Regional Water Board by May 2018. The LAMP is an application by the County that demonstrates compliance with the State’s OWTS Policy.

What is the County’s OWTS Manual?

The OWTS Manual is a compilation of Sonoma County’s regulations and standards regarding on-site septic systems. In the past, individual regulations were created as needed and placed into a binder by date created. The collection of regulations soon became unwieldy. The OWTS Manual brings all the regulations and standards together into one document which is organized as a technical manual.

How do the existing County regulations fare in comparison to the new State OWTS Policy?

The vast majority of the County’s current program is consistent with the state's policy.

What is the difference between the State OWTS Policy and the County’s current OWTS regulations?

The State’s OWTS Policy requires a two foot separation to groundwater regardless of the treatment level or effluent quality. The County’s current OWTS regulation allows shallower disposal based on effluent quality and/or raising the dispersal above grade. A second difference is the State defines a replacement dispersal system to include installing leach lines for an existing OWTS. Replacement dispersal systems are to meet the same standards as a new dispersal system. The County has had the flexibility to accommodate leach lines for existing OWTS in the past. These were called voluntary repairs which sometimes included leach lines.

The County’s proposed OWTS Manual seeks to reconcile these two provisions with those required by the State’s OWTS Policy.

How much is the County OWTS Manual changing compared to previous/existing County septic regulations?

The vast majority of requirements are not changing. The primary revisions in the proposed manual include updates to: septic review for building permits, voluntary repairs and replacement systems, designer/contractor requirements, experimental and alternative systems, water re-use/gray water.

Where can I read the revised OWTS manual?

The revised OWTS manual was adopted on August 15, 2019. You can read the OWTS manual online.

When will the new regulations go into effect?

The Board of Supervisors will meet and discuss the revised OWTS Manual and potentially authorize submittal of the County’s Local Agency Management Program to the Regional Water Board. Regional Water Board approval is needed prior to the regulations going into effect. For important dates, go to the Revision Milestones & Community Feedback section of the main OWTS revision page.

Who will be affected by the County's OWTS Manual?

Potentially anyone constructing or permitting a septic system and some people obtaining building permits for structures connected to septic systems.

How will these proposed changes to the OWTS Manual impact me as a property owner?

The County only gets involved for two reasons:

  • The OWTS system is failing or has surfacing effluent or
  • The property owner submits for a building permit or septic permit

In these cases you may need to upgrade or replace your existing OWTS and the new standards would apply. How the standards affect your situation varies based on the following:

  • Building proposals and the lot size
  • Soils type
  • Slope of lot
  • Bedrooms
  • Proximity to groundwater
  • Existing septic systems
  • Existing wells
  • Distance to creeks
  • Etc.


What type of work requires a permit for a new septic system?

  • Constructing a dwelling unit on undeveloped land requires a new OWTS.
  • Constructing a dwelling unit on developed land may require a new OWTS.
  • Constructing an accessory dwelling unit on developed land may require a new OWTS.
  • Constructing a new or replacement septic system requires a septic permit.

What type of septic work requires a replacement permit?

Replacement of the septic tank; replacement of more than 25% of the dispersal system; or replacement of a pretreatment unit.

What type of septic work requires a repair permit?

  • Replacement of 25% or less of the dispersal system.
  • Replacement or repair of the leach line, whole or segment, within an existing trench.
  • Repair of the pretreatment unit.

What septic work is permit exempt?

  • Risers
  • Sanitary tees
  • Effluent filters
  • Diversion valves
  • Distribution box
  • Sewer line from house to septic tank
  • Sewer line from tank to distribution box
  • Solid sewer line connecting distribution boxes

What building permits trigger a septic review?

Building permits that require a set of plans.

What building permits do not trigger a septic review?

Septic review is not required for building permits that do not require sets of plans:

  • Furnaces
  • Water heaters
  • Re-roofs
  • Siding
  • HVAC
  • Electric service
  • Electric repairs
  • Interior wall covering
  • Dry rot repair (greater than 40 linear feet)
  • Deck repairs

What is the building permit septic review process?

Sonoma County Code requires the Well and Septic Section to review and clear building permit applications for structures that connect to an OWTS (new dwellings), or where a proposed alteration/modification imposes additional burdens upon existing systems (adding a bedroom or increasing the waste flow) or where property is being improved in excess of its capacity to absorb sewage effluent (additions, new square footage, or accessory structure physically impacting a system and/or replacement area(s)).

These types of building permits will be routed to the Well and Septic Section for their review and comments.

Building projects that add/increase wastewater will need to demonstrate or construct a code compliant system. Building projects that do not add or increase wastewater will need to demonstrate an existing OWTS. All building projects will be evaluated relative to their footprint and how it affects the current system and replacement reserve areas.

What type of building projects create an increase in wastewater flow?

Adding bedrooms or commercial processes involving increases in water use.

What land constraints are considered during the septic review process?

Land encumbrance includes paving or covering the land with structure(s), setbacks from wells, septic creeks, and steep or cut slopes. When reviewing your building permit application, staff would determine whether the proposal encumbers the parcel to the point that the replacement reserve septic area needs to be properly established.

Can I build an accessory dwelling unit without increasing septic capacity?

Maybe. If you increase the overall wastewater flow on the property, you’ll need to ensure that you have adequate septic capacity for this increase. This can be done by evaluating the capacity of an existing system or constructing a new system. Another approach is to offset the increase by reducing the number of bedrooms in the primary dwelling. Regardless, a septic tank is needed for the accessory dwelling.

What is a code compliant septic system?

A code compliant system meets the standards outlined in the OWTS Manual, or meets the intent of the standards by proposing mitigation measures that are equal to the standards. 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.

How much will it cost if I need to replace my septic system?

Costs vary, but here are some estimates:

  • $5,000 Replacement Tank
  • $10,000-$15,000 Replacement Dispersal System
  • $20,000 Standard System
  • $70,000 ATU/UV Disinfection / Dispersal

Under the new regulations, how long will it take to have my septic permit reviewed and approved?

Our target is to review and approve septic permits within 6 weeks. For emergency repairs, we will expedite the review. See Permit Sonoma’s current permit processing time.

What Ifs

What if I have a failing system and can’t afford to fix it?

The County of Sonoma and the Regional Water Board are committed to identifying options for individuals and communities affected by these regulatory changes. Property owners will be responsible to privately finance OWTS replacement or upgrade costs, like the way they would pay for costs incurred to replace a roof or repair and seal a busted foundation.

If the site cannot accommodate a code compliant system or it is too expensive, the owner may apply for a financial hardship permit. If the land owner qualifies for the financial hardship (80% of the Area Median Income or less), the County can authorize a system that best fits the site. However, the hardship permit would not authorize construction to the structure. The hardship permit is intended to fix the septic system only.

What if I can’t meet the required two foot separation to groundwater?

If the proposed septic system cannot meet the two foot separation standard then the customer will have to apply to the local water board to obtain a waiver and work with Permit Sonoma regarding the technical aspects of the design. The County cannot waive this standard according to the state's OWTS Policy.

I have my septic tank pumped out every few years for regular maintenance. Could the septic pumper’s report cause a problem for me?


What if my system doesn’t meet the revised OWTS manual requirements? Will the County condemn my property?

No. If your septic system is operating properly the County has no legal authority to condemn your home or even enter your property.

What if my septic system works just fine? How will the new OWTS Manual affect me?

Properly functioning septic systems will not be affected by the revised OWTS Manual. OWTS Manual requirements will apply if you:

  1. propose to increase the volume of wastewater the existing septic system will receive or
  2. replace either your existing septic tank or dispersal field.

Design and Operations

Who will be authorized to design standard septic systems?

The state requires septic systems to be designed by registered civil engineers and registered environmental health specialists.

Why do you require civil engineers and registered environmental health specialists to design septic systems?

These are the two professionals who are licensed by the State of California to evaluate soils and to do design work. Soil scientist and geologist can do the soils evaluation, but can’t do the design work. Contractors are licensed to construct systems but are not authorized to evaluate soils nor to perform design work.

How does the County determine the size requirements of a septic tank and dispersal field?

The size of the system depends on the amount of wastewater going to the system (typically the number of bedrooms), the type of soil, the percolation rate of the soil, the depth of the soil and the distance to groundwater.

How many linear feet of leach line are required per bedroom?

The linear footage varies by soil type. Per bedroom, the linear footage ranges between 60 feet for a course sand / loamy course sand to 375 feet for a clay / silty clay. This assumes two feet of trench side wall (one square foot on each side of the trench) below the dispersal pipe for each linear foot of leach line.