Shallowly placed, low pressure distribution system to treat domestic wastewater in soils with fluctuating high water tables
1988
Stewart, L.W. | Reneau, R.B. Jr
Soils with seasonal fluctuating high water tables are common in the Atlantic Coastal Plain and are considered to be unsuited for conventional on-site wastewater disposal systems (OSWDS). This study was conducted to monitor the performance of a shallowly placed, low pressure OSWDS in a Typic Ochraquult. Low pressure distribution and shallow placement were used to achieve uniform distribution and maintain an unsaturated zone in the more biologically active upper soil horizons. This combination was used to reduce movement of bacteria and P while utilizing water table fluctuations to enhance denitrification. Changes in water table levels, effluent distribution, and movement of fecal coliforms and selected chemical contaminants in ground-waters were monitored in situ from December 1980 through May 1982. An unsaturated zone was present beneath the OSWDS during the entire study except for the period from January through May of 1982. During this period the water table intersected the OSWDS, for some time interval (less than 24 h), on 36 d primarily following large rainfall events. Movement of fecal coliforms and P were restricted both horizontally and vertically. Nitrate concentrations were highest beneath the OSWDS during periods of rising water tables following prolonged periods of time when the water table was deeper than 1.5 m. Following the accumulation of NO3(-)-N in the upper portion of the water table, NO3(-)-N concentrations decreased rapidly. The observed decrease in NO3(-)-N was attributed to denitrification and was supported by NO3(-)-N/Cl- ratios. Based on NO3(-)-N/Cl- ratios, approximately 90% of the NO3(-)-N could not be accounted for with increased distance from the OSWDS.
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