Percolation Testing and Septic System Design in nevada County, California
If you’re planning a residential or commercial septic system in Nevada County, California, understanding the county’s requirements for percolation testing, septic sizing, and septic design is essential to ensure your system functions properly and receives county approval. Nevada County’s Local Area Management Plan (LAMP) governs how onsite wastewater systems are evaluated, sized, designed, and permitted under California’s statewide On‑Site Wastewater Treatment System (OWTS) Policy — protecting public health and water quality across the region.
What Is the Nevada County LAMP?
Nevada County’s LAMP, adopted as part of the county’s land use and development code, sets minimum standards for design, construction, installation, monitoring, maintenance, and repair of onsite sewage disposal systems (septic systems). It works alongside the state OWTS Policy to ensure consistency with accepted engineering practices while considering local soil, topography, and environmental conditions.
Percolation Testing & Soil Evaluation Requirements
Before applying for a septic permit in Nevada County, you must complete percolation testing and soil evaluation as part of a site evaluation. The purpose of percolation testing is to measure how quickly water is absorbed by the soil — a key factor in septic sizing and septic design.
Key soil testing requirements under Nevada County’s LAMP include:
A minimum of two soil test pits in the area proposed for waste disposal must be excavated prior to permit application, unless sufficient existing information is already on file. These pits must be witnessed by the county and the applicant’s consultant.
Percolation tests must be performed by a qualified professional and a minimum of three tests are required in the proposed disposal area when percolation tests are used for sizing the septic system.
Wet weather testing may also be required to determine the depth to water and soil saturation at representative times of year.
These tests help you and the county determine soil texture, permeability, groundwater conditions, and any restrictive layers that could affect system performance.
Who Can Prepare Your Soil Evaluation and Perc Tests
According to Nevada County’s LAMP and Environmental Health guidance, qualified professionals are required to conduct onsite soils evaluations and percolation testing. A qualified professional is defined under county regulations to include:
Certified Engineering Geologists
Certified Professional Soil Scientists
Registered Civil Engineers
Registered Environmental Health Specialists
These specialists perform the soil test pits, interpret the results, and prepare your site evaluation report (also referred to as an On‑Site Soil Evaluation or OSSE Report) which is required for septic permitting.
Site Evaluation and Documentation
Before a construction permit can be issued, Nevada County requires a Site Evaluation Report (OSSE Report) prepared by your soil consultant and reviewed by a county Environmental Health Specialist. This report includes:
Results of soils testing
Percolation test data
Identification of suitable and replacement disposal areas
Observations of constraints such as steep slopes, rock outcrops, or high groundwater
A detailed site plan showing property boundaries, existing and proposed structures, wells, water lines, soils test locations, and the proposed septic system layout
Having a complete and accurate site evaluation report is critical to getting your septic system permit approved without delays.
Septic Sizing & System Design
Once soil conditions and percolation rates are determined, the next step is proper septic sizing and septic design:
Septic sizing is based on percolation test results or soil type, expected wastewater flow (for residential — usually tied to bedrooms; for commercial — based on business use and flow demands), and required vertical separations.
System design considers soil absorption, depth to groundwater, slope, setbacks, and projected load to ensure the leach field and septic components are suitable for long‑term performance.
Designs prepared by a qualified professional must accompany your permit application if your system requires engineered calculations or is a non‑standard system type.
Nevada County’s approach ensures that septic systems are sized appropriately for soil conditions and wastewater flows, which helps prevent failures and protects local water resources.
Setbacks and Environmental Protection
Nevada County’s Environmental Health also enforces setback requirements to safeguard drinking water wells, surface waters, and neighboring properties. For example, onsite wastewater systems must meet minimum horizontal distances from water bodies, wells (including those on adjacent parcels), and other sensitive features. These distances and setback requirements can be found through Nevada County Environmental Health resources.
System Permitting & Final Approval
When your septic design, soil reports, and site plans are submitted and meet all LAMP and OWTS requirements, Nevada County Environmental Health reviews your application for compliance. Once approved:
A septic construction permit is issued.
Required inspections are conducted during installation.
A Certificate of Satisfactory Completion is issued only after the system has been inspected and verified to meet the approved plan and county standards.
Nevada County also includes provisions for variances if standard requirements cannot be met due to unique site constraints, provided that public health and environmental protection are maintained.
Residential vs. Commercial Septic Designs
The LAMP applies to both residential and commercial septic systems in Nevada County. Smaller residential systems typically follow standard designs based on soil and flow, while commercial systems or non‑standard systems often require more detailed engineered designs and calculations from a qualified professional on the site evaluation and septic design documents.
How STL Can Help With Your Nevada County Septic Project
At Soil Tests Laboratory, we provide complete support for percolation testing, soil evaluation, septic sizing, and septic design in Nevada County, California. Our team works with qualified professionals — including soil scientists and certified designers — to prepare your site evaluation report, perform accurate percolation testing, and develop septic designs tailored to your property’s soil and conditions.
From initial soil assessment through permit application and final compliance, STL ensures your project meets Nevada County’s LAMP and state septic requirements — helping you avoid costly delays and build with confidence.
Contact us for a price at: Info@soiltestslab.com or call (951) 345-3509
