Test Pit Information 

A number of different types of septic systems are now approvable in Oregon.  Each type has different soil and topographic requirements.  We evaluate the test pits you've provided, to determine the appropriate type of septic system for your lot.  If approved, the drainfield will be located in the vicinity of the test pits.

To perform the Site Evaluation, you must provide at least two test pits (preferably three).  Pits should be 50-100 feet apart.  Test pits need to be large enough for us to enter and inspect the soil profile (two (2) feet wide, four (4) feet long, and five (5) feet deep) and stepped or ramped on one end for safe access.

A plot plan must be submitted with the application that clearly shows the location of the test pits, all wells (including the neighbors), and property lines.  The plot plan should also show the location of any proposed or existing development such as buildings, roads, and wells.  Show all features in relation to the test pits.  The drainfield cannot be located in areas that are to be covered by the proposed home, driveway, or accessory buildings.

Notify us when test pits are ready for inspection.  To help us locate your property, place the green card, with the site inspection number on it, in a location that can be seen from the road.  Provide a marked trail if the test holes cannot be seen from the road.  Open test pits are a potential hazard; keep them covered to prevent accidents.  Test pits can be a breeding ground for mosquitoes, as well as, a safety hazard to people and animals.  Test pits should be promptly backfilled upon completion of the site evaluation.

Do NOT modify (cut or fill), dig a nearby well, pave, or otherwise develop the proposed and/or approved-drainfield location.  Doing so could void your approval.

Siting Considerations

  • Test holes need to be within the area that is proposed for the drainfield; not at the edge of the property or simply where access is easy.  If the lot is heavily vegetated, some clearing of vegetation may be necessary for equipment access and so that we can measure distances.
  • There are setback requirements for drainfields.  Test pits should be:
    • 100-150 feet from any well or year-round surface water,
    • 50-100 feet from intermittent streams,
    • 20-30 feet from property lines, and
    • 20-30 feet from any existing or proposed foundations.
  • Landscape Position:  Look for areas with some slope.  Avoid flat poorly drained positions where water may collect during the wet season -- raised anthills and rush (wire grass) indicate poorly drained soils.  Avoid concave positions (swales) where surface water is likely to collect.  We cannot approve sites with slopes greater than 45%.
  • Select a site that has smooth topography (without irregular humps and bumps).
  • Avoid areas that have been modified by filling, grading, or heavy traffic.  Do not dig in road-beds.  Dig at least 25 feet up from road cuts, or sharp-slope changes, that exceed 30-inches in depth.
  • Select an area for test pits where there is adequate available space for a septic system and full sized repair.  An area 100 x 100 feet is usually large enough for the initial, and repair, system.