A 4,000 gpd reverse osmosis unit was tested on a severely polluted ferrous iron acid mine discharge near Morgantown, West Virginia. The water recovery rate was limited to fifty percent due to membrane fouling problems. The role of ferrous iron fouling could not be identified because of a predominance of calcium sulfate precipitation on the membranes. The feasibility of reverse osmosis treatment is doubtful for mine drainage having concentrations of acidity, iron, sulfate, and calcium as high as 5,000 mg/l, 2,300 mg/l, 10,000 mg/l and 525 mg/l, respectively, due to the membrane fouling problem, maximum recoveries of only 50 percent, and the non-potable quality of the product water. (Author)