Vadose Zone Transport of Nitrate in the Sierra Pelona Groundwater Basin, Agua Dulce, California

摘要

Using data from previous studies about nitrate contamination in Agua Dulce, CA andthe numerical modeling program HYDRUS-1D, nitrate transport in the vadose zoneassociated with septic system discharges was evaluated. Thirty-six modelingscenarios were assessed and the results analyzed. With soil borings less than 6 mdeep, steady state nitrate transport within the system is reached within 200 days,while steady state is not reached with the deeper boring within 500 days. Themodeling results show that the nitrate concentration plume is less than the maximumcontaminant level (MCL) of 10 mg/L within 1.3 m below the septic leachfield in allscenarios. The analysis of the fully-mixed tank scenario clearly shows that nitrateconcentrations in groundwater are of greater concern during drought conditions.These findings help explain the pattern of nitrate concentrations observed in theaquifer system in this region.