Soil and Site Evaluation for Onsite Wastewater Treatment

Bulletin 905

Completing the site and soil assessment

The soil pit examination should reveal no surprises though every location is different. Steps 1 through 4 should lead the system designer to the appropriate areas of the site for wastewater treatment and aid in selecting the proper system type for the site conditions. The soil pits, excavated for Step 5 are critical in confirming the suitability of the site for wastewater treatment.

Once the soil pits are scheduled for excavation, make a site evaluation appointment with the responsible regulator. Before issuing a permit for a wastewater treatment system, the regulator must check to make sure the site and its proposed wastewater treatment system will work to protect the public health and the environment.

The regulator should make the following observations when viewing the soil pits.

• The soil present at the site is the same as that mapped or consistent with the mapping unit descriptions. If not, why not.
• The site has not been modified by human activity. Evidence of soil erosion, compaction, excavation, fill or other modifications should be observed or ruled out.
• Confirm the depth to the limiting condition and the permeability of all soil horizons.

Make sure provisions are in place to protect the wastewater treatment system from damage during building construction and use of the property.

• Note the proposed location of structures, driveways and landscaping changes.
• Make sure they will not cause excess surface water to drain onto the area for the wastewater treatment system. Also, no structures or driveways should be sited just downslope of the wastewater treatment system.
• Make sure fences and signs are put up, if needed, to protect the soil being used for the wastewater treatment system from compaction and damage during site development.
• Finally, date and sign the site and soil assessment. Property owners sometimes change their mind and do not proceed with land development projects in a timely manner. As time passes or property changes hands, the site can be disturbed or considered for development in different ways. A new site and soil assessment may be needed if too many changes occur.