Percolation Testing and Septic System Design in Placer County, California
Planning a residential or commercial septic system in If you’re planning to build a home, ADU, or commercial property in Placer County, California, understanding the county’s requirements for percolation testing, septic sizing, and septic design is critical. Placer County administers its own Local Agency Management Program (LAMP) under the California Onsite Wastewater Treatment System (OWTS) Policy, giving the county flexibility to tailor siting and design standards to local conditions while still protecting groundwater and public health.
What Is the Placer County LAMP?
Placer County’s Local Agency Management Program ensures compliance with the state’s OWTS Policy and establishes permitting standards for new and replacement septic systems. The LAMP includes a Sewage Disposal Ordinance and a Sewage Manual that outline how onsite wastewater systems must be evaluated, designed, and installed.
Recent updates to the LAMP are designed to lower costs, simplify language, and support additional dwelling units (ADUs) while maintaining environmental safeguards. These changes include adjustments to sewer connection distances, more septic options, and revised tank size allowances.
Percolation Testing & Soil Evaluation
For most new systems in Placer County, percolation testing or an equivalent soil evaluation is required before a septic permit can be issued. If your property does not already have a valid soils testing report on file, Environmental Health will require testing to determine whether the soil can support an onsite wastewater system.
What percolation testing and soil evaluation accomplish:
Determines how quickly water drains through the soil, which guides septic sizing and dispersal field design.
Identifies soil textures, restrictive layers (such as clay or shallow bedrock), and groundwater conditions that could affect system performance.
Helps Environmental Health determine the type and location of the septic system best suited to your site.
In Placer County, soils testing is typically conducted by an approved sewage disposal consultant alongside a representative from Environmental Health, with results documented in a Soils Evaluation Report for approval.
Test Pits and Soil Profile Investigation
Although the Placer County LAMP doesn’t publish a single online list of minimum pit widths or depths in its summary, standard practice for septic design across California counties includes excavating test pits to expose the soil profile. These pits:
Allow trained professionals to inspect soil horizons and textures.
Reveal restrictive layers like bedrock or hardpan.
Show groundwater influences, including seasonal high water table levels.
Provide data used to calculate appropriate septic sizing and dispersal area.
In Placer County, soils consultants and county staff work together on site to evaluate soils and make these determinations as part of the percolation and mantle tests.
Septic Sizing and System Design
Once percolation testing and soils evaluation are complete, the next step is septic system design and septic sizing:
Residential systems: Designed based on soil percolation rates, expected wastewater flow (often tied to number of bedrooms or occupants), and local setback requirements.
Commercial systems: Typically require more detailed designs due to higher flows or unique site conditions; these designs often must be prepared or reviewed by a qualified professional familiar with county codes.
Setbacks and separations: Systems must meet minimum horizontal setbacks from wells, property lines, structures, and water bodies and maintain adequate vertical separation from groundwater or restrictive soil layers.
The Placer County Sewage Manual within the LAMP includes detailed design criteria, construction specifications, and permitting processes to ensure systems perform well and protect public health.
Recent LAMP Updates That Affect Septic Projects
Placer County’s LAMP has been updated to:
Reduce sewer connection distance: The distance at which properties are required to connect to sewer has been lowered, easing costs for homeowners.
Expand septic installation options: Including provisions that support ADUs connecting to existing systems when capacity exists.
Provide more flexibility for repairs and replacements: In some cases allowing repair instead of mandatory sewer connection if economic thresholds are met.
These changes make it more affordable and practical for homeowners and developers in Placer County to pursue septic solutions where appropriate.
How Placer County’s LAMP Fits Into California
Placer County’s septic design requirements are governed locally by the LAMP, but they still operate within the statewide OWTS Policy framework, which allows local programs to adopt tailored siting and design standards—as long as they protect water quality and public health.
How STL Can Help With Your Placer County Septic Project
At Soil Tests Laboratory, we provide full-service assistance for percolation testing, soil evaluation, septic sizing, and septic design in Placer County, California. Whether you’re building a residential home, installing an ADU, or designing a commercial septic system, our team can handle the technical soil work, testing coordination, and design documentation required for county approval. From initial evaluation through final permit submission, STL ensures your system is compliant, functional, and tailored to your site’s unique conditions.
Contact us for a price at: Info@soiltestslab.com or call (951) 345-3509
