Eighteen sources of drainage related to past coal-mining activity were identified in the Claybank Creek, Missouri, study area, and eight of thew were considered large enough to have detectable effects on receiving streams. However, only three sources, coal wastes at Keota and Binkley, and drainage from underground coal mines near Keota, significantly affected the chemistry of water in receiving streams.

Coal wastes in the Claybank Creek basin contributed large quantities of acid drainage to receiving streams during storm runoff; pH of coal-waste runoff ranged from 2.1 to 2.8. At these small pH values, concentrations of some dissolved metals and dissolved sulfate were a few to several hundred times larger than Federal and State water-quality standards established for these constituents. Effects of acid storm runoff were detected near the mouth of North Fork Claybank Creek where the pH during a small storm was 3.9.

Coal wastes in the streambeds and seepage from coal wastes also had significant effects on receiving streams during base flows. The receiving waters had pH values between 2.8 and 3.5 and concentrations of some dissolved metals and dissolved sulfate were a few to several hundred times larger than Federal and State water-quality standards.

Most underground mines in the North Fork Claybank Creek basin are hydraulically connected and about 80 percent of their discharge surfaced at one site. Drainage from the underground mines contributed most of the dissolved constituents in North Fork Claybank Creek during dry weather. Underground-mine water always had a pH near 5.9, was well-buffered, had a dissolved-sulfate concentration of about 2,400 milligrams per liter, dissolved-manganese concentrations ranging from 4.0 to 5.3 milligrams per liter, and large concentrations of ferrous iron. Iron was in the ferrous state due to reducing conditions in the mines. When underground-mine drainage reached the ground surface, the ferrous iron was oxidized and precipitated to form large, orange deposits of ferric hydroxide around the site and in streambeds.

Generally, drainage from strip mines had dissolved-sulfate concentrations several times larger than drainage from unmined areas. However, effects of drainage from strip mines on receiving streams were minimal when compared to the drainage from coal wastes and underground mines.

No appreciable effects of mine-related drainage were detected in the water of the Claybank Creek arm of Thomas Hill Reservoir at the time of sampling because beaver bogs upstream had trapped suspended coal wastes and moderated the effects. However, the concentration of coal in the bottom material was 60 percent of the coal concentration in coal wastes at Keota, indicating that the reservoir had received these wastes during the past.