Septic systems/onsite wastewater treatment systems

An onsite wastewater treatment system (OWTS) is also called a septic system. A septic system is like an individual wastewater treatment plant for your property. It has two main parts: a septic tank and a drain field (also known as a leach field). The tank separates the solids from the liquid waste. The liquid is disposed of in the soil via piping. The soil treats the contaminants in the sewage through biological, physical, and chemical processes. 

Modern septic systems serve homes and properties with poor or difficult site conditions. Most modern septic systems are more advanced in their design. They have extra components such as pumps, multiple tanks, and pretreatment units. Systems using pretreatment are also called "alternative systems."

A working septic system ensures proper wastewater disposal. This is important in protecting the environment and public health.

There are two categories of septic systems: 

Standard: A septic system composed of a tank and drain field. This system may include a separate tank with a pump for dispersal up slopes or over long distances.

Alternative: An alternative system treats the sewage to a higher degree before disposal. Alternative systems must be used when site conditions or soils are limiting. Find out which type of alternative system you need by talking to your septic system designer. You can also contact our office to speak with EHS staff. Alternative systems are site specific, so no one system type can meet the needs of every property. You will need an annual operating permit and professional monitoring for your alternative system. This is necessary to make sure that the system is functioning correctly. 

Class I - Code complying system

Class I system is an onsite wastewater treatment system that follows all current Marin County regulations for design, construction, and repair of individual sewage disposal systems. A Class I system has a dual leach field (200% sizing) and meets all of the siting and design criteria.

Class II - Repair standards

Class II system is an onsite wastewater treatment system that does not follow all current regulations. A Class II system has a 100% sized field and meets much of the siting and design criteria.

Class III - Existing systems

Existing systems: Class III system is one that received a permit under the current or previous regulations. The system is not in full compliance with the current regulations. It also does not meet the minimum standards for a Class II system. 

Class IV - Undocumented and/or unapproved systems

A system may be classified at Class IV for one or more of the following reasons: 

1. The septic tank is made of unapproved materials such as redwood, steel, or cinder blocks.
2. The system utilizes a cesspool.
3. The system has no documentation i.e., no permit record. Some systems may be retroactively permitted.
4. The system is failing. Some systems may retain original class status once repaired. 

If your residence is served by a septic system and you wish to make improvements, remodel, or add to your residence, refer to the Residential Improvement Policy for guidance. The County's Building and Safety Division classifies building permit applications. Permit applications that involve septic systems are routed to our office for review.

See the Residential Improvement Policy in the document list below. 

Call us at 415-473-6907 for any questions about your septic system. We will help you determine how to apply this policy to your project.

• Download the document septic system permit application.
• Submit the completed application to our office. We will need three copies of the plans or site map (where applicable) to process your application. You can mail or bring your application to our office. You can submit your application by email and then deliver or mail the plans.
• An application fee is due upon application submittal. See the fee schedule in the documents list below. You can pay the fee by calling us during office hours once the documentation has been submitted.

• You can apply for a site evaluation through our office. EHS staff will meet on site with your septic designer. See heading below "How to Apply for Services and Permits".
• Conduct percolation testing with the septic designer. Our staff must be present for this test.
• Apply for a septic construction permit.
• Obtain the permit to construct a septic system. (Additional permits or permissions may be required for properties in the Coastal Zone or the Stream Conservation Area).
• EHS staff will conduct several construction inspections throughout the installation process.
• After we have determined that the system is installed in accordance with the approved plans, we'll issue a certificate of installation.
• Depending on the system type, an operational permit may be required. You will hold this permit for the life of the system.

• Replacing/repairing a septic tank
• Excavating of the disposal field or alteration/replacement of any disposal field components
• Replacing the sand media or gravel within a pretreatment unit or disposal field
• Replacing the pretreatment unit or other system component
• Abandoning a septic tank or a septic system

• Repairing plumbing outside of the disposal field (may require a plumbing permit from the Building Department)
• Replacing or maintaining pumps or control panels (may require an electrical permit from the Building Department)
• Purging or routine maintenance of the disposal field
• Sealing, repairing, or installing risers or effluent filters

You might have a simple pipe clog or your septic system might be failing if:

• You are smelling foul odors
• Your sinks or toilets are not draining well
• You see sewage surfacing in your yard or home

Call your septic service provider to assess the problem. You may need to contact a licensed sewage hauler to pump the tank. This will help with the troubleshooting process. 

If a system failure is suspected, your septic tank can be capped off to stop more sewage from surfacing. The tank will serve as a holding tank until the system can be repaired. Contact an approved septic designer to start the process to permit a replacement or repair. Check the documents list below for approved septic service providers, contractors, and designers.