Soil physical and chemical studies of five subsurface septic tank seepage beds were conducted to determine the biochemical transformations of N and thereby its potential for ground‐water pollution. Effluent was found to be ponded in all the seepage beds examined due to the presence of an impeding layer, a “crust”, at the boundary between the gravel bed and adjacent soil. The crust reduced infiltration rates approximately from 500 to 8 cm/day. Soil atmospheric composition 5 cm below the crust averaged 19.6% O2 and 0.66% CO2. Nitrogen in the septic tank effluent occurred as NH4‐N (80%) and organic N (20%) with virtually no NO3‐N. Organic‐N was largely concentrated in the crust zone. Nitrification of NH4‐N to NO3‐N was essentially complete and commenced in the unsaturated subcrust soil within about 2 cm of the crust. Nitrification did not occur and NH4‐N was absorbed by the soil below a seepage bed that was submerged in the ground water.
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Walker et al. (1973) studied this question.