Nitrogen transformation in the subsurface during effluent recharge

Abstract

The transformation of nitrogen in treated effluent during recharge at the Sweetwater Underground Storage and Recovery Facility was examined. The procedure consisted of obtaining samples of percolating water and groundwater below a 3.3 acre infiltration basin, carried out over the recharge season October 29, 1991 - May 23, 1992 and during an entire 4 day wetting/6 day drying cycle. Nitrate concentrations decreased in the profile and in groundwater throughout the season. During the wetting/drying cycle the nitrate level decreased from a maximum of over 20 mg/L NO₃⁻-N at a depth of 5 feet to about 10 mg/L NO₃⁻-N at 17 feet. Below 17 feet, the nitrate level remained approximately constant. A 36% reduction in total nitrogen concentration was observed between source water and groundwater. Results suggest that soil aquifer treatment (SAT) may be useful in reducing the total nitrogen concentration of effluent.