07/19/2026
So what is the County or the Soil Scientist looking for when they “perc” your land? Actually it is now referred to as site and soil evaluation and not a perc test. In NC and especially in our area the most obvious thing they are looking for is soil depth. For any septic system, yes “engineered” systems too, there must be 18” of soil. Of that 18” you need a minimum separation of 12” from rock or a restrictive horizon and 6” from a soil wetness condition, ie seasonal high water table which is indicated by gray mottled soil. Other criteria they look for is soil texture which is the amount of sand, silt and clay that’s present in the soil, soil consistency which is how firm the soil is, and clay mineralogy for clayey soils which is how sticky and plastic the soils are. If a soil is too firm it is too compact/tight and harder for effluent to pass through. If the clay is too sticky and plastic this means the clay particles swell when wetted thereby sealing off the pores and not allowing effluent to permeate the soil. These are all field test that are performed by the evaluator with the soil in a moist condition, usually wetted up using a water bottle. So what’s the difference between most county evaluators and a soil scientist? In NC most county evaluators go to class for 2-6 weeks. Soil Scientist have a 4-year degree, 3 years working under another soil scientist and have to pass a 2 part licensing test. Also, don’t expect a soil scientist to evaluate and permit your property for a few hundred dollars. The county can do this because they are supported by your taxes and are self insured. Most soil scientist charge several thousand dollars depending on how much land they have to evaluate and the system type required.
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