ARSD 74:53:01:15. Separation required above groundwater or geological formations

There shall be at least 4 feet of soil between an absorption bed, trench, or seepage pit bottom, the lowest construction joint on a septic tank, or any other component of a subsurface absorption system and the seasonal high groundwater table, groundwater table, rock formations, or impervious soil strata. Absorption systems shall not be constructed in soils rated as having severe or very severe limitations for underground dispersal by the soil conservation service, U.S. department of agriculture, unless that limitation is not present as shown by field investigation or unless prior written approval is granted by the secretary.