A subsurface clay dike and hydraulic seals were constructed in 1979 by the Ohio Department of Natural Resources, Division of Reclamation, to reduce acid mine drainage from an abandoned drift mine into Big Four Hollow Creek; Big Four Hollow Creek flow into Sandy Run, the major tributary to Lake Hope. A monitoring program was established in 1979 by the U.S. Geological Survey, Water Resources Division to evaluate sealing effects on surface-water and ground-water systems fo the Big Four Hollow Creek and Sandy Run area just below the mine. Data were collected by private consultants in 1970-71 near the mouth of Big Four Hollow Creek (U.S. Geological Survey station (03201700). Results showed an average pH of 3.1 (calculated from mean hydrogen-ion concentration in moles per liter) and a pH range of 2.7 to 4.8. The estimated sulfate load was 1,000 pounds per day, and the estimated iron load wsa 100 pounds per day. Data collected in 1979, before dike construction at this site, showed a daily mean pH range of 3.4 to 5.4 with an average of 3.7, and a daily mean specific-conductance range of 160 to 600 micromhos per centimeter at 25 degrees Celsius (?mho/cm), averaging 400. Again, the estimated sulfate load was 1,000 pounds per day, but the estimated iron load had decreased to 50 pounds per day. The first 6 months of postconstruction data from the site in 1980 showd a daily mean pH range of 4.5 to 6.8 with an average of 4.9, and a daily mean conductance range of 175 to 405 ?mho/cm with an average of 300. The estimated sulfate load had decreased to 570 pounds per day and the iron load to 8.5 pounds per day. Data collected during the first 6 months after construction indicate moderate improvement in water quality. However, acidic water is still being impounded behind the dike and seals and has not yet been flushed ou by infiltrating rain and ground water. Because the system has not yet stabilized, no interpretation or conclusive statement can be made at this time.