Deep, permeable soils are ideal for wastewater treatment and dispersal. In Ohio, a depth of 4 feet of unsaturated soil is needed to renovate wastewater to meet standards of organic matter, suspended solids, ammonia, bacteria, and virus removal.
Efficient wastewater treatment in soil to remove contaminants relies on aerobic processes. Soil must be sufficiently permeable to allow for the passage of both wastewater and air. Most importantly, the soil where treatment occurs must remain unsaturated year-round. If wastewater is discharged into saturated soil, pollutants are not adequately treated or removed, and may move quickly over large distances (hundreds of feet) with groundwater, emerging in ditches, streams or lakes, or contaminating nearby wells.
In much of Ohio, the soil is not deep enough to provide for adequate treatment of applied wastewater. However, where some unsaturated soil is available, the natural soil can often be augmented with layers of selected sand to create the necessary depth of treatment to renovate the wastewater and disperse it. Mound systems and sand bioreactors can be used throughout much of Ohio to treat and disperse wastewater. The depth of soil above a limiting condition and the permeability of the soil material are both important factors to be considered when siting and designing any wastewater treatment and dispersal system.
For information on mound systems and sand bioreactors, ask for Bulletins 813, 829, 876 and 912 for sale through Ohio State University Extension offices. They can be found and downloaded online at www.ag.ohio-state.edu/~setll.