Nitrogen Transformations During Subsurface Disposal of Septic Tank Effluent in Sands: II. Ground Water Quality
1973
Walker, W. G. | Bouma, J. | Keeney, D. R. | Olcott, P. G.
Ground water observation wells were installed in the immediate vicinity of four septic tank effluent soil disposal systems. Potentiometric maps were constructed from measurements of the groundwater level at each site to establish the direction of movement. Ground-water samples were pumped from each well to establish patterns of N enrichment in the ground water around the seepage beds and to evaluate the performance of these disposal systems in sands in terms of N removal. Soil disposal systems of septic tank effluent in sands were found to add significant quantities of nitrate (NO₃-N) , formed by nitrification of NH₄-N , the dominant N form in the effluent, to underlying ground water. The data obtained suggest that in sands, the only active mechanism of lowering the NO₃-N content is by dilution with uncontaminated ground water. Relatively large areas of 0.2 ha (0.5 acre) down gradient were needed the studied systems before concentrations in the top layer of the ground water were lower than 10 mg/liter. The average N-input per person was 8 kg (10 Ib) per year. Essentially complete nitrification in the soil results in addition of approximately 33 kg NO₃-N (73 lb) to the ground water per year for an average family of four.
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