The first step of installing a new septic system is ensuring the site can meet the owner's needs. A Perc and Mantel is a soil water absorbsion test done to determine what type of septic system the property can accomodate. Navo & Sons, Inc has a septic design professional on staff, and we perform our own Perc & Mantel testing, unlike other septic companies in the area.


Soil test pits or soil mantles are excavations done with a backhoe to verify effective soil depth. Effective soil is considered soil that will treat or filter sewage. For a standard sewage disposal system (in our counties) a minimum 6 feet of effective soil is required, 4 feet of effective soil below the trench bottom. The standard trench depth is 24-inches.


Percolation test are used to determine how fast or slow water will filter through the soil. A perc hole is dug to the anticipated trench bottom or to the limiting horizon. The hole is pre-soaked to simulate winter time or wet weather conditions. Readings of how quickly water leaves this hole are taken the following day. These reading are then averaged to calculate your average percolation rate.

What is an O.S.S.E.

Before applying for a new septic system, it is necessary to have a valid soils testing (On Site Soils Evaluation - OSSE) done. An OSSE includes soil tests that determine the effectiveness of soil to filter sewage through leach lines, as well as observations of required setbacks, constraints and possibilities for an individual, “on-site” septic system. The Soils Evaluation Report produced by the consultant of the particular site tested on a parcel is reviewed and evaluated by an Environmental Health Specialist who generates a findings report. An OSSE must be conducted by a Nevada County approved Soil Testing Consultant. Soils Evaluation Reports are valid for 3 years. Consultant re-certification is required for any reports exceeding 3 years.

It is recommended to have the consultant apply for the OSSE permit, as well as schedule inspections to conduct the OSSE. This can be done by calling the inspection line, (530)265-1599. Once the OSSE has been completed and signed off by the Environmental Health Specialist, you can proceed to apply for a Septic Permit Application.

Quick steps to apply for an OSSE/ Perc & Mantle

  1. Hire a Nevada County Approved Soils Testing Consultant (Navo)
  2. Your Consultant (Navo) will Apply for the OSSE using some forms you will fill out
  3. Consultant (Navo) schedules an OSSE
  4. Consultant (Navo), Backhoe operator (Typically Navo) and Nevada County Specialist meet on site for soils testing
  5. Consultant (navo) submits Soils Evaluation Report to Nevada County
  6. Nevada County Specialist generates Findings Report to approve what type of septic system to install
  7. AFTER This a design can be created by your Consultant (Navo) to apply for the permit and get an install estimate
  8. You may then proceed to apply for a Septic Permit

More information

Process To Install The Average Septic System in Nevada County

Process To Install The Average Septic System in Placer County