Distribution of nitrate in ground water, Redlands, California

Abstract

The distribution of nitrate in ground water in the Redlands area is dependent primarily upon depth below the water table and areal location. Concentrations of nitrate as nitrogen exceeding 10 milligrams per liter are generally found within the upper 50 feet below the water table in the study area, with the exception of the areas in and adjacent to the Santa Ana River and Mill Creek channels. 1 Concentrations of nitrate as nitrogen less than 10 milligrams per liter are found throughout most of the area at depths below the water table of 300 feet or greater. This depth dependence suggests that the major source of nitrate is a generalized area-wide infiltration of high-nitrate water downward from the surface through the unsaturated zone. The largest point source of nitrate in the study area is from the Redlands sewage-treatment facility. The high-nitrate concentrations presently found along the Santa Ana River channel, downgradient from the Redlands sewagetreatment facility, probably came from the nearby previously used facility which was abandoned in 1963. The nitrate concentration in water from individual wells is dependent primarily upon depth and well construction—particularly aquifer seal and aquifer penetration—and secondarily upon well location. Nitrate concentrations of water in wells are increased by heavy pumping which causes localized depressions of the water table and which subsequently causes the high-nitrate water near the water table to be pulled deeper and to constitute an increasing fraction of water produced by the well. The results of this study and the data collected before and after the 1969 flood, which caused an abnormally large rise in the water table, suggest that increased nitrate concentrations in water from wells can result if a rising water table intercepts high-nitrate, downward-infiltrating water in the unsaturated zone. titrate concentrations are expressed in terms of an equivalent amount of nitrogen (U.S. Environmental Protection Agency, 1972). DISTRIBUTION OF NITRATE IN GROUND WATER, REDLANDS, CALIF,