Concentrations of chloride were greater than the Secondary Maximum Contaminant Level (250 mg/L) in 2.3 percent of the samples from 869 monitoring wells, and 1.8 percent of the samples collected from 532 drinking water supply wells. Sodium concentrations were greater than the Drinking Water Advisory of 20 mg/L in samples from 56.7 percent of monitoring wells in urban areas, 16.9 percent of samples from monitoring wells in agricultural areas, and 7.3 percent of the monitoring wells in forested areas.  Sodium concentrations were greater than the Drinking Water Advisory in 47.5 percent of samples from public drinking water wells and 34.4 percent of private drinking-water wells.

An analysis of chloride-bromide ratios and chloride concentrations in samples from monitoring wells and drinking water wells indicated mixed sources of chloride (including halite dissolution and sewage or animal waste) in many of the samples, but higher concentrations were dominated by halite dissolution.

Surface-water quality data were analyzed from 31 urban and 20 forested basins.  Eleven of the urban basins contained major wastewater discharges. Twelve of the 51 sites had chloride concentrations greater than the U.S. Environmental Protection Agency recommended chronic aquatic criteria concentration of 230 mg/L. Concentrations of chloride exceeding the chronic criteria typically occurred during the winter months, indicating a possible relation with road deicing.  Base-flow chloride concentrations greater than 75 mg/L were indicative of sites with maximum measured chloride concentrations greater than 230 mg/L.  The median yield of chloride was 86 tons per square mile per year from the urban basins and 7 tons per square mile per year from the forested basins.