The quality of water in the principal aquifers of southwestern Washington

The quality of water in major aquifers in southwestern Washington was addressed in terms of inorganic-constituent, trace-metal, and fecal-coliform concentrations. Results of this assessment indicate that the groundwater in southwestern Washington can be characterized as soft to moderately hard with a low concentration of dissolved solids. Nitrate was the only constituent found at concentrations above maximum contaminant levels specified by the U.S. Environmental Protection Agency primary drinking water regulations. The most prevalent detriment to the otherwise good quality of groundwater in the region was concentrations of iron and manganese that exceeds limits recommended by the U.S. Environmental Protection Agency secondary standards. Although these limits were exceeded in less than one half of the samples, high concentrations of iron and manganese were common throughout the entire region.