Septic system leach fields require deep, permeable soil to treat and safely dispose of wastewater. The Ohio Administrative Code (1977) requires a 4-foot-deep soil layer between the bottom of a sewage leaching trench and a limiting soil condition (Figure 2). If the trench bottom is 18 inches beneath the soil surface, a total of 5.5 feet of soil depth is required above a soil limiting condition of ground or perched water tables, hard, unfractured bedrock, dense glacial till, compacted zones, dense clays, pans such as fragipans, sand and gravel layers, and fractured rock.
Table 1 lists by name the soil series that are in the range of soil depths and permeabilities to be suited for septic system leach fields. The 84 soil series are present in 6.4% of Ohio's land area. Figure 3 shows where in Ohio these soil series are distributed. Remember, these soil series are used to describe soils over a range of depths. As shown in Figure 4 one of the soils listed ranges from 5 feet to 6 feet of depth above a limiting condition. Some of these depth differences are natural and some are the result of erosion and human activities. It is necessary to check the soil depth to a limiting condition in a soil pit before designing, building, or approving a septic system leach field.