AGRONOMY GUIDE
PURDUE
UNIVERSITY
AY 179
Urban
Houses, Septic Systems and Soils
Joseph E. Yahner, Agronomy Department
Trees, green lawns, room to live, space for the family — these ideas are attracting an ever increasing number of people to the suburbs. The possibility of lower taxes, investment for the future and an almost certain rise in land prices and building costs are stimulating this movement.
Most suburban-country or farm homes use septic systems for their sewage disposal. Thirty-six percent of all American homes do. These systems use the soil to absorb the septic effluent which is distributed by tile in trenches or beds.
It is estimated that an average of 80 to 100 gallons of water are used in a home per person per day. This adds up to 150,000 to 180,000 gallons per year for a family of five. Most, if not all, of this water must pass through the septic system into the soil. When soil conditions are not suitable, failures occur. These failures range from non-operating home facilities to contamination of local water supplies. A knowledge of some of the soil’s characteristics will help identify possible problem areas and hopefully increase the chances of design of a suitable system.
The following pointers will help identify some soil characteristics related to the success or failure of septic systems.
Soil Permeability
Permeability is the speed with which water enters and passes through a soil.
It is influenced largely by the amount of clay, sand, silt and gravel in the soil and by the tightness or looseness of the arrangement of these particles. High clay or compact soil layers can slow down water movement until the soil cannot accept the daily volume of septic effluent. Morley, Blount, Vigo and similar high clay soils have very slow permeability in their subsoils.
A properly conducted percolation rate test gives an idea of the soil permeability. It is , however, very difficult to run to obtain reproducible results.
The Indiana State Board of Health recommends that soils requiring more than 60 minutes for water to fall one inch in a percolation test hole should not be used for septic tile fields. Many soils of central and southern Indiana will have percolation rates at or above this rate.
Water Table
Absorption tile will not work in a soil where the water table rises to the tile depth. The soil pores are filled with water and no room is left for septic effluent.