Site Evaluations

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Site Evaluations and Soil Profiles for Septic System Design

Site Evaluation on a large parcel

Site Evaluation on a small parcel

Why are Site Evaluations necessary?

site.eval.septic.exampleOnsite Wastewater Treatment Systems, also known as septic systems, treat domestic sewage/wastewater from dwellings. It is like a mini-sewage treatment plant right on your parcel, that treats ("cleans") the wastewater so that it can re-enter nature.  The soil is an important system component used to treat the wastewater as it percolates down through the ground, before it reaches groundwater or other limiting layers such as hardpan or rock. Septic systems should also not be too close to waterways, water wells, or other features. We all want septic systems to work properly, and this begins with a Site Evaluation.

What is a Site Evaluation?

A Site Evaluation is an assessment of the characteristics of a parcel to determine its suitability and sustainability of a septic system, meeting the requirements of the Yolo County Code. The site evaluation will take into consideration the public and environmental health aspects relating to the installation and operation of a septic system, including but not limited to: soil texture, soil structure, soil percolation rate, depth to groundwater or other limiting layer (i.e., vertical setbacks), distance from natural land features and man-made structures (horizontal setbacks), site topography, and usable space for the installation and repair of a septic system.

What is the Site Evaluation process?

  1. Hire a Septic Qualified Professional (QP). This is an individual licensed or certified by the State of California and who has been approved by Environmental Health to perform Site Evaluations, and to practice as an expert as allowed under their license or registration and as demonstrated by their possession of knowledge and skills of soils and septic system design and installation. Share with your QP the entire scope of your project. Click here for a list of Septic Qualified Professionals.

  2. Submit a Site Evaluation Request and form and fee to Environmental Health. Click here for the Site Evaluation Request form, and click here for the fee schedule.

  3. Schedule the Site Evaluation with Environmental Health at least 48 hours in advance. Coordinate with your QP a date and time to conduct the site evaluation. Schedule with Environmental Health the time when the soil pits will have been dug and profiled by your QP; your QP shall be present at the same time as Environmental Health. (A backhoe operator may also need to be scheduled if your QP does not provide this service).

  4. Site Evaluation is performed. A minimum of two (2) pits are dug to a minimum depth of eight (8) feet; however, the number and depth of the pits could vary based on site, design, and project. Unless otherwise determined, at minimum there shall be one pit dug in the primary septic system area, and a second pit in the septic system replacement area. Horizontal and vertical setbacks are identified, and soils are evaluated for a possible wastewater application rate for treatment. (Although not required in Yolo County, your QP may also conduct Percolation Tests).

  5. Complete the Site Evaluation. A Site Evaluation is not considered complete until a Site Evaluation Report by your QP is submitted to Environmental Health for review and approval.

  6. The next stage of your project
    • Septic Installation Permit: If you require a new septic system or a modification to an existing septic system, submit a Septic System Installation Permit, with the appropriate fee and septic design, for review and approval.
    • Septic System Evaluation: If you are wanting to use an existing septic system for a project, submit a Service Request form, with the appropriate fee and supporting documentation, for a Septic System Evaluation. Click here for a Septic System Evaluation Informational handout.
    • Building Permit Approval: After a Site Evaluation is complete (a QP Site Evaluation report is submitted), Environmental Health can approve the issuance of a building permit.

Contractor digging a soil profile pit


Septic Qualified Professional evaluating the soils.
He is picking through the soil horizons.


Inspector validating soil horizons and evaluating
the soil and structure.
(Measuring the depth to different soil horizons).


Collection of soil for field evaluation.


Soil "ribboning" - to determine soil classification..


USDA Soil Classification System
Soil and septic design discussion with owner and
contractor (Qualified Professional is in the pit).


Site and septic design discussion between inspector and
Qualified Professional - determining site restrictions.


Soil pit and measuring tools to assess the site.

Measure to surface features, such as onsite wells
(soil pits in the distance).

Evaluating an existing system with no permit on file.
Expose system for measurements
(septic tank lids are removed for inspection).

(Soil profile pits in the distance)

Evaluating an existing system with no permit on file.
D-boxes are exposed to verify depth of system.