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This article in JEQ

  1. Vol. 2 No. 4, p. 475-480
    Received: Feb 15, 1973

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Nitrogen Transformations During Subsurface Disposal of Septic Tank Effluent in Sands: I. Soil Transformations1

  1. W. G. Walker,
  2. J. Bouma,
  3. D. R. Keeney and
  4. F. R. Magdoff2



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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