Public Water Supply Quality in the Rock River Watershed, Southwest Minnesota

Abstract

Several municipal water supplies in the Rock River watershed in Southwestern Minnesota were tested on approximately a monthly basis for a little over two-years for the anions nitrate-nitrogen, sulfate, chloride, and bicarbonate alkalinity as calcium carbonate, and for total dissolved solids, conductivity, and pH. Anions were selected for analysis because it was felt that they were better descriptors of the effect of land use practices on ground water quality. The ratios of the various anions sulfate/nitrate-nitrogen, chloride/nitrate-nitrogen, sulfate/chloride, and bicarbonate alkalinity as calcium carbonate/sulfate served to identify changes in water quality not associated with dilution. Findings indicated seasonal changes in water quality not necessarily reflected in changes in the ratios, generally increasing concentrations of nitrate-nitrogen in many instances, exceeding permissible concentrations specified in the Interim Primary Drinking Water Standards, and high dissolved solids concentrations generally exceeding recommended levels specified in the Secondary Drinking Water Standards. Groundwater concentrations were compared with surface water samples from the several streams, springs, and lakes in the area. Some relations to land use practice on groundwater quality and precipitation were indicated. The data have been utilized to call attention to deficiencies in water quality to the consumers of the waters in the communities concerned.