In Ohio, almost one million homes are beyond the reach of community sewage systems (Bureau of Census 1990). Each year many more homes are built in rural Ohio and all must consider treating and disposing of wastewater on the lot. The soil on the lot is often considered the best medium to treat and dispose of the wastewater to protect the health of the family, neighbors, and visitors as well as the environment that all Ohioans treasure.
Ohio has wonderfully diverse soil resources. Each of Ohio's nearly 500 soil series have been characterized by the National Cooperative Soil Survey. Tabulated and assessed by a group of soil scientists, the soil depth to bedrock, depth to a limiting soil condition, depth to seasonal saturation, and soil permeability are just some of the characteristics described in 88 individual county soil surveys.
Onsite sewage treatment system designers, planners, installers, and regulators all can use this valuable information to help select the most appropriate wastewater treatment and disposal systems for a tract of land. Of course, soil is usually not present in the landscape in discrete units, but rather as a continuous pattern of gradually varying conditions and capabilities to renovate sewage effluents. The soil maps presented in soil surveys, therefore, serve as a guide to help assess the extent and diversity of the soil resource but do not aim to delineate short-range variations in soil attributes. Before an individual system is sited and designed, a detailed site and soil assessment must be conducted to gain understanding of specific local conditions.
The soil's ability to purify wastewater has been recognized for decades. The goal in any sewage treatment system is to remove pollutants such as disease-causing organisms, ammonia, organic matter, and solids, before the wastewater reaches ground or surface water. Naturally occurring soils have varying capacity to accomplish pollutant removal to protect the water resource. While many soil processes assist in wastewater treatment, three properties are recognized as the most important: