The U.S. Bureau of Mines is conducting research in hydrochemical modeling and physical property analysis to determine the mechanisms causing differential attenuation of downgradient metal concentrations. An abandoned copper-gold tailings impoundment and an unconfined downgradient groundwater system were monitored for 2 yr. Water samples from the saturated zone of the tailings were analyzed for 12 constituents. Concentrations of the same constituents were determined in water samples up to 3 m (10 ft) beneath the tailings and in the shallow colluvium and deep bedrock at distances about 76 m (250 ft), 335 m (1,100 ft), and 550 m (1,800 ft) downgradient of the impoundment. Metal concentrations were also determined in shallow and deep zones upgradient of the impoundment (background). The results show that concentrations of almost all dissolved metals were substantially less in water samples taken from immediately beneath the tailings than in water samples taken within the tailings, and that concentrations of all constituents decreased with distance downgradient. However, levels of calcium, magnesium, manganese, and sulfur did not return to background levels at the well farthest downgradient, while levels of sodium actually increased.
Proc. Western Symp. on Mining & Mineral Processing Wastes, Berkeley; SME, 1990, PP. 133-142