Pennsylvania has an abundant supply of surface water of good quality. The average rainfall over the 45,300 square miles in the State is about 42 inches per year. Of this amount, about 50 percent appears in the streams as runoff. The combined mean annual runoff of the Delaware, Ohio, and Susquehanna Rivers, at their farthest downstream measuring points in the State, is in excess of 81,000 cubic feet per second. Variations in the chemical quality of the surface waters in Pennsylvania are caused by areal differences in geology, urban and industrial development, mining, quarrying, land use, and runoff. Waters having the least dissolved solids are found in the glaciated northeastern and northwestern parts of the State; waters having higher values of hardness are found in the limestone terranes in the southeastern and south-central parts. In the anthracite coal fields in the northeast and in the bituminous coal fields in the southwest, many streams receive acid mine drainage, which lowers the alkalinity and increases the sulfate content of the waters. The chemical quality of surface waters in Pennsylvania is discussed in general terms. Introductory sections of the report cover the main causative factors which influence chemical quality.
