The most important aspect of an OSSF design is an accurate site evaluation of the property by a professional site evaluator. Our job as a site evaluator is to assess site conditions, drainage, and soil types and determine the best type of OSSF for each particular property.
First, we have to determine the most suitable site location for the proposed OSSF. Considerations include drainage, setbacks from property lines, water wells, easements, recharge features, slope, lot size, and flood hazards.
Once the location is determined, a minimum of two soil profile holes must be excavated to a minimum depth of 48 inches towards each end of the designated area. The best method for profile hole excavations is with a backhoe, because it provides the most accurate visual profile of the soils.
By visual inspection of the profile holes, the evaluator looks for signs of restrictive horizons such as rock, dense clay strata, or groundwater that could hinder the movement of water downward and through the soils.
If there are no restrictive horizons present, a soil analysis is performed on the most restrictive soil present to determine soil texture and classification.
Once the soils are properly classified, the proper type of OSSF can be determined. The size of the OSSF is then determined according to the number of bedrooms, square footage, and the number of occupants on the property (for commercial facilities, the number of employees and building usage determines the OSSF’s size).