Site Evaluation Guide

A site evaluation is the process to determine whether a particular location on a given property may be suitable for the installation of a new septic absorption system, and may be required to replace or relocate an existing system.  The site evaluation process takes the place of the largely obsolete percolation, or ‘perc’ test, and relies in part on an examination of test pits to determine whether a site’s suitability.  An approved site evaluation is required to apply for most types of septic construction permits.

Site criteria

We look at several factors to determine whether a site may be suitable for a septic system, including:

  • Soil conditions as demonstrated by examination of test pits
  • Presence of relatively shallow groundwater or saturated soils
  • Slope of the property
  • Location of any existing septic systems
  • Presence and location of any surface waters, drainage features, existing/proposed structures, pools, cuts or filled areas, and other items requiring a setback

Application process

Site Evaluations for new or existing septic systems may be applied for via Development Direct.  Please visit our How to Apply for a Permit page for more information on the application process.

Due to the number of applications we receive, it may take several weeks for us to complete your Site Evaluation, so we recommend you apply as soon as you are ready.  This is especially true during the drier portions of the year, when our application volumes tend to increase substantially. 

Unfortunately, due to our application volumes, it is not possible to schedule a specific time for a site evaluation, as we schedule these to be as efficient as possible with other fieldwork.

Note: An Entrance Permit may be required to construct an access point to the property. Contact Transportation Engineering for more information.

To ensure the quickest and most accurate possible analysis of your site please pay special attention to the following guidelines. Sites that do not adhere to the following risk denial or an extended review time.

Test pits

View Test Pit Preparation for Onsite Sewage Evaluations

  1. Provide a minimum of two test pits (maximum of six).
  2. Test pits must be dug per Test Pit Preparation guide.
  3. Keep the "spoils" pile at least two feet away from the edge of the test pit.
  4. Test pits should be spaced 100' apart in the area where you intend to locate the original and replacement drainfields.
  5. Locate the test pits in an area no smaller than 100' x 100' and no larger than five acres.
  6. Test pits should be located on the driest part of the property and should not be located within any of the setbacks listed on the DEQ setback table . (see setback list).
  7. Test pits must be dug when you apply. Failure to have test pits dug when our inspector visits the site will result in your project being delayed.

Site preparation

  1. If the test pits are not easy to find, mark a trail to them in the field.
  2. Identify the property corners on site using clearly marked stakes or similar means.  Any easements on the property should also be clearly identified.


The applicant will be notified by mail or email of the site evaluation results.  If a site is found suitable for a septic system, a report will be provided prescribing the minimum type of system required based on current DEQ codes.  Not all sites are suitable for a ‘standard’ system; in those cases, alternative systems will be prescribed based on conditions observed at the site.


150 Beavercreek Road 2nd floor Oregon City, OR 97045

Office Hours:

Monday, Tuesday, Thursday  
8 a.m. to 4 p.m.

Available by phone/email  
8 a.m. to 4 p.m.  
8 a.m. to 3 p.m.