Septic Conversions


Septic System Conversions
Converting From An Individual Private Septic System To Central San Public Sewer Service

Central San is an independent special district that collects and treats wastewater for ten cities and many unincorporated areas in central Contra Costa County.  When the time comes to abandon an existing septic system and convert to public sewer, a Central San sewer permit is required prior to starting any of the exterior sewer work. If you are uncertain if you can continue to use, repair, or replace your property’s existing septic system, please reach out to Contra Costa County Environmental Health Division as they are the governing agency over septic systems.  

To start the septic conversion process, a completed Residential Application for Wastewater Utility Service will need to be completed and emailed/mailed to or dropped off at the permit counter. When completing the application form, you will need to include the number of residential units on the property (main house, ADUs, apartments, etc.) and what other structures on the property (outdoor kitchens, accessory buildings, etc.) will be connecting to sewer. Once the application is received and reviewed, staff will determine if the property is within Central San boundaries, if annexation is required, and if public sewer is readily available to connect to. Staff will reach out with any additional information needed to accept the application and prepare a fee quote with the sewer connection and permit fees for you.  

If you are only contemplating connecting to the public sewer system and would like to know if public sewer is readily available for your property to connect to or if you would like an estimate for of sewer fees, please email the permit counter. A property address or Assessor Parcel Number (APN) is required in order for staff to prepare a fee quote. Additional information such as the number of residential units on the property, number of structures that will be connecting to sewer, the need for a sewage pump, and estimated linear footage of sewer pipe to be installed will help staff in providing a fee quote.  

In 2022 Central San launched the Septic to Sewer pilot program. The program provides a low interest financing option for property owner who are converting their property over to public sewer from a private septic system. To learn more about this pilot program, please visit our Septic to Sewer webpage.

Frequently Asked Questions

1. Why convert from a septic system to Central San sewer service?

CCEH considers use of septic systems in an urban or suburban setting to be a temporary means of wastewater treatment and disposal.  Septic systems have limited life spans and some property owners may not have sufficient land with an adequate percolation rate for a replacement or reserve leach field area when the existing system fails.  In such cases, the only alternatives available may be an expensive, engineered septic system or abandonment of the septic system and connection to the public sewer system.  CCEH is the public agency that will make the determination if a property can continue using a septic system. Additionally, if your property is within 300 feet of an existing Central San sewer, CCEH may require you to connect to the sewer when your existing system fails or if you are planning substantial improvements to your home. 

Converting from an individual private septic system to public sewer may increase the market value of your property.  Additionally, if your existing septic system is failing, the market value of your property can decrease until you fix the situation by repairing/replacing your septic system or connecting to Central San’s sewer system.  Also, since septic systems are unpopular with most homebuyers and can limit the ability to expand your house or build over portions of your property, having a septic system will result in your property being less marketable at time of sale, as compared to similar sewered properties.

2. Will building a public sewer promote growth in my neighborhood?

Central San is not a land-use planning agency; this is a city/county responsibility.  Sewers are designed to accommodate the number of existing and future homes that are allowed by the current city/county general plan and land use zoning.  The presence of a sewer system may affect the rate of home building in an area, especially those areas that have a septic tank moratorium or have soils that require an engineered individual waste treatment and disposal system.

3. What are the costs involved in converting from a septic system to Central San sewer service?

There can be four major costs in converting from a septic system to sewer service:  sewer availability, side sewer construction, Central San Fees, and septic tank abandonment.

Sewer Availability - The first cost depends on whether a public sewer is adjacent to your property and suitable for your use.  A public sewer is usually eight inches in diameter and may be located in a street or a sewer easement through private property.  If a public sewer is available adjacent to your property, a developer, one or more of your neighbors, or an assessment district involving many property owners may have constructed it.  Depending on the circumstances, the original installer(s) of that sewer might be owed a reimbursement (a share of the cost of construction) when a new connection occurs, or there may be no reimbursement involved.  Central San staff can determine the situation with your individual property.  If there is a reimbursement due, it will be collected by Central San at time of connection and disbursed to the installer(s).

If no suitable public sewer is available, you will be responsible for extending a public main sewer from the end of Central San’s existing system to your property.  Central San is prohibited by law from constructing main sewer extensions for private property.  Central San builds the larger trunk and interceptor sewers that transport wastewater out of neighborhoods to our wastewater treatment plant in unincorporated Martinez near the I-680/SR 4 interchange.

The cost for you to extend a public main sewer to your property can run approximately $200 per linear foot, or more, depending on the difficulty of the terrain, geotechnical concerns, need to acquire easements, amount of engineering work required, pipe and backfill materials specified, methods of construction employed, and surface restoration requirements.  This estimate also includes Central San’s fees and charges to cover its expenses to process permits, review design plans, process right-of-way documents and inspect the construction work.  In rare cases, you may also owe a reimbursement to the installer of “special” public sewer facilities constructed downstream of the sewer you install. 

The cost of this work can sometimes be shared with your neighbors who also would benefit from the availability of a public sewer adjacent to their properties.  Longer, shared sewer projects allow for an economy of scale in design and construction that reduces the cost per property, as compared to each property owner sequentially installing a separate, smaller sewer extension project. Depending on the method of financing (see Question 4), this cost may be paid directly by the property owners to the engineers and contractors they hire to do the work, or may be payable over time, either by means of privately obtained financing, or as an assessment on your annual property tax bill.

Side Sewer Construction – A side sewer is generally a four inch pipeline that runs from your house to the public sewer.  A gravity flow design from your house to the sewer is preferred.  Central San may allow the installation of an individual residential pump if a gravity system is infeasible.  The property owner is responsible for obtaining permits and constructing the side sewer. A portion of this sewer (known as a lateral sewer) may have been stubbed out from the public sewer to your property when it was constructed.  Property owners may do work on their own property, provided the trench needed for the installation will not be deeper than five feet, but construction within public right-of-ways or Central San easements requires hiring a properly licensed contractor registered with Central San. 

The existing pipeline from the house to the septic tank may be used as part of the new side sewer only if it is a minimum of four inches in diameter and passes a District-witnessed pressure test.  A side sewer is then constructed the rest of the way (sometimes wrapping around the house) to the public sewer.  Alternatively, plumbing beneath the house sometimes can be redirected toward the public sewer so as to avoid having to construct a pipeline around the house. Alterations to any plumbing within the house requires a permit from your local building department. The cost for this work is paid directly by the property owners to the contractor they hire at the time the work is done. Central San encourages property owners to obtain at least three (3) quotes from different contractors for any proposed sewer work. 

Central San Fees – Central San collects fees to cover its costs to provide services and facilities to the property owner.  These fees pay for processing permit and annexation applications, inspecting the installation and connection, providing collection system and treatment plant capacity, and a portion of the first year’s Sewer Service Charge (SSC) for operations and maintenance.  All but the SSC are one-time charges.  Total fees currently vary from about $9,200 to $10,200 per residential unit, depending on location.  These fees are due just prior to connection to the public sewer. The largest portion of these connection fees can be financed through Central San on your property tax bill.

Septic Tank Abandonment – CCEH requires that septic tanks be properly abandoned when no longer needed.  The test of the existing side sewer as well as the installation of the new side sewer must be completed and accepted before the existing septic tank is removed from service and abandoned. 

The abandonment process involves obtaining a permit from CCEH; having the tank pumped out one last time; removing and disposing of the lid; and filling the empty septic tank with compacted dirt or sand.  Specific requirements for septic tank abandonment can be obtained from CCEH.  Any costs associated with the abandonment process are paid directly by the property owner to CCEH and to the contractor at the time the work is done.

4. How can a new public main sewer extension project be financed?

Public sewer extensions are constructed and financed by individual property owners, developers, one or more neighbors working together, or an assessment district.

Developer - In the case of an established neighborhood with septic systems, the original developer may be long gone, but sometimes a new developer needs to build a sewer through the neighborhood to get to an undeveloped site. If it is affordable, the developer may use private funding to build the new public sewer extension and have Central San collect a reimbursement from property owners of existing homes as they directly connect to that new public main sewer extension.  The reimbursement amount would be a proportional share of the cost of constructing the sewer extension.

Other Private Installers – Much like the developer, one or more neighbors could pool their private funds to construct a public sewer extension to serve their properties.  Again, Central San would collect a reimbursement from other property owners as they directly connect their homes to that new public sewer extension and disburse the funds to the original installer(s). 

Contractual Assessment District (CAD) – The only form of financing currently available through Central San to assist property owners extend public main sewers is the CAD. A CAD is a financing arrangement that allows sewer planning, design and construction costs to be divided proportionally among the property owners who voluntarily choose to participate in paying for the sewer project.  The sewer costs are financed over time by Central san, which is repaid by annual assessments from property owners on their property tax bills.

5. Why do property owners favor or oppose Contractual Assessment Districts?

Reasons property owners give for supporting a CAD include:

  • wanting to replace their failing septic system;
  • proposing an addition or other property improvement not accommodated by their existing septic system (as determined by CCEH);
  • preferring sewer service over septic for operational or property-marketing purposes;
  • desiring the ability to finance their assessment over a long period of time;
  • appreciating the environmental benefits of decreasing the number of poorly operating septic systems in their neighborhood that may pollute nearby creeks; and
  • ensuring a public sewer is available if and when needed, thus being prepared for a sudden septic system problem in the future (a property owner can participate in the CAD and choose to delay actual connection to the public sewer until a later time).

Reasons property owners give for opposing a CAD include:

  • not wanting to incur a multi-year assessment at this time; and
  • not wanting to sewer an area because of concerns about growth.

6. How long does it take to design and construct a public sewer extension?

Most public sewer extensions, if built privately, could be completed in six to eight months.  The process of designing a public sewer extension can take about four to six months (but sometimes longer), depending on the workload of the engineer hired, the complexity of the design, and the quality of the work (determines the number of Central San plan reviews required).  Once the design is completed, a contractor is hired and all permits have been obtained, construction of most public sewer extensions can be completed within several weeks (barring bad weather).  If significant street repaving is involved, that work may be delayed until the weather is warm enough to allow the paving materials to cure properly. 

If built as part of a CAD, the design and construction time is the same as above, but additional time is needed at the beginning and end of the process due to the formalities of initiating CAD formation.

7. How much is Central San’s annual sewer service charge?

Once connected to the Central San sewer system, a property owner is required to pay an annual sewer service charge.  This charge covers the operation and maintenance costs for collection, treatment, and disposal of wastewater, and renovation of the sewers and wastewater treatment facilities. This charge appears as a separate line item on the annual property tax bill of those properties connected to Central San’s public sewer system.  Central San’s elected Board of Directors reviews and sets this charge annually.  State law requires customers to be notified in advance of future increases and allowed an opportunity to be heard and protest. Please click here to view the current SSC and other Central San rates and fees.