Nitrogen Isotope Monitoring at Unsewered Subdivisions

Introduction: On-site septic-tank, soil absorption systems which serve unsewered subdivisions may cause nitrate-nitrogen levels in ground water to exceed the national drinking water standard of 10 mg/L of nitrate-nitrogen. Tinker, Jr. (1991 and 1990) analyzed water samples for nitrate-nitrogen from private water-supply wells in six subdivisions in Wisconsin. The nitrate-nitrogen values were analyzed for their distribution within the subdivision and for their relationship to the location of upgradient septic systems. In addition, Tinker, Jr. (1991) describes the application of a combined nitrogen mass balance model of Wehrmann (1984) and the BURBS nitrogen mass balance model of the Center of Environmental Research, Cornell University (1985) to the six subdivisions. The results of this investigation concluded that nitrogen from lawn fertilizer and septic-tank, soil absorption systems cause nitrate-nitrogen values to increase in the ground water beneath and on the downgradient side of the six subdivisions.