Two studies related to the regional environmental effects of coal mining in the Appalachian Plateau were conducted in 1998 as part of the National Water‐Quality Assessment program of the U.S. Geological Survey. The study area of about 20,000 square miles included parts of the Allegheny and Monongahela River basins in the north and the Kanawha River basin in the south. Water in domestic wells downgradient from fully reclaimed surface coal mines was compared to water in similar wells at unmined sites. As expected, pH was lower and the concentration of sulfate was greater at mined sites in both areas, although the pH difference was greater in the southern area. Median concentrations of iron and manganese exceeded federal drinking‐water standards at mined sites in both areas and at unmined sites in the southern area. Median concentrations of radon near reclaimed mines were about half those at unmined sites.

Surface water was sampled during summer base flow at about 180 sites that drain between 5 and 80 square miles; the sites also were sampled during 1979‐81. Median pH in 1998 was 7.9 in the north and 7.4 in the south, about 0.5 unit higher than in 1980 in both areas. Median concentrations of sulfate increased from 38 mg/L to 56 mg/L in the north and from 46 mg/L to 77 mg/L in the south, in apparent contradiction to the generally lower sulfur content of geologic units in the southern area. Among 52 basins where mining occurred both before and after 1980, the sulfate concentration more than doubled in 13 (25 percent), including greater than five‐fold increases in 5 (10 percent). For 16 mined basins where no mining has occurred since 1980, the median decrease in sulfate concentration was 18 percent, from which the half‐time for oxidation of mining‐related pyrite is estimated to be about 65 years.