CHANGES IN CONCENTRATIONS OF SELECTED CHEMICAL POLLUTANTS IN WET, TILE-DRAINED SOIL SYSTEMS AS INFLUENCED BY DISPOSAL OF SEPTIC TANK EFFLUENTS

Changes in P, MBAS, NH//4, NO//3, NO//2, Cl, pH, and Eh from septic effluent disposal were monitored in shallow ground waters between septic effluent disposal fields and an agricultural tile drainage system in an area composed of Typic and Aeric Ocraquults. As effluent moved through the soil system toward the agricultural tile, P and MBAS decreased logarithmically with distance. Phosphorus and MBAS in ground waters intercepted by the tile drainage system at two of the sites had been reduced to acceptable levels. The concentrations of inorganic nitrogeneous components in relation to the disposal area were similar at all three locations. The NH//4-N concentration was highest adjacent to the drainfield (20-30 mu g/ml) and decreased logarithmically with distance. The NO//3 concentration increased to a maximum at approximately 5 m and then decreased with increased distance. The NO//3 accumulation was seasonal with the highest concentrations present during periods of rising water tables.