The streams in the 2,000-square-mile Erie-Niagara basin of western New York contain mainly a calcium bicarbonate type of water whose dissolved-solids content generally varies between 140 and 240 ppm (parts per mill ion). Water "hardness" (expressed as CaCO3 ) is usually between 100 and 200 ppm, sulfate concentrations are between 20 and 60 ppm, and chloride between 5 and 20 ppm. The higher concentrations of these constituents and properties are representative of the northern part of the area, which is underlain by the gypsum-bearing Camillus Shale. The northern part of the area contains a predominantly calcium sulfate type of water that usually has a dissolved-solids content of between 250 and 750 ppm, sulfate between 40 and 350 ppm, chloride between 20 and 70 ppm, and hardness between 200 and 500 ppm.