Abstract: The Kidd Creek Cu-Zn sulphide mine is located near Timmins, Ontario. Mill tailings are thickened and deposited as a thickened slurry in a circular, conical-shaped pile with an area of approximately 1200 ha. Deposition of tailings as a thickened slurry results in a relatively uniform grain-size distribution and hydraulic conductivity, and a thick tension-saturated zone above the water table. The tailings are drained by numerous small, ephemeral stream channels, which have developed in a radial pattern. During storms, water from these streams collects in catchment ponds where it is held before treatment. The contribution of tailings pore water to the run off is of interest because of the potential for discharge of pore water containing high concentrations of Fe(II)-acidity, metals and SO4 to the stream. Hydraulic head measurements, measurements of water-table elevation and groundwater how modelling were conducted to determine the mechanisms responsible for tailings pore water entering the surface streams. Chemical hydrograph separation of storm run off in one of these streams, during three rainfall events, using Na and Cl as conservative tracers, indicates that the integrated tailings pore water fraction makes up between less than 1% and 20% of the total hydrograph. This range is less than the maximum fraction of tailings pore water of 22-65% reported for run off from a conventional tailings deposit. At this site, preferential flow through permeable fractures may be the dominant mechanism causing discharge of tailings pore water to storm run off. Estimates of the mass of Fe(II) that discharges to the surface run off from the pore water range up to 2800 mg s(-1) during a moderate intensity, long duration rainfall event. The greatest potential for discharge of significant masses of solutes derived from the pore water exists during long duration rainfall events, when the water table rises to the surface over large areas of the tailings impoundment.

Abstract: The Summitville Mine Superfund Site is located about 25 miles south of Del Norte, Colorado, in Rio Grande County. Occurring at an average elevation of 11,500 feet in the San Juan Mountain Range, the mine site is located two miles east of the Continental Divide. Mining at Summitville has occurred since 1870. The mine was most recently operated by Summitville Consolidated Mining Company, Inc. (SCMCI) as an open pit gold mine with extraction by means of a cyanide leaching process. In December of 1992, SCMCI declared bankruptcy and vacated the mine site. At that time, the US Environmental Protection Agency (EPA) took over operations of the water treatment facilities to prevent a catastrophic release of cyanide and metal-laden water from the mine site. Due to high operational costs of water treatment (approximately $50,000 per day), EPA established a goal to minimize active water treatment by reducing or eliminating acid mine drainage (AMD). All of the sources of AMD generation on the mine site were evaluated and prioritized. Of the twelve areas identified as sources of AMD, the Cropsy Waste Pile, the Summitville Dam Impoundment, the Beaver Mud Dump, the Reynolds and Chandler adits, and the Mine Pits were consider to be the most significant contributors to the generation of metal-laden acidic (low pH) water. A two part plan was developed to control AMD from the most significant sources. The first part was initiated immediately to control AMD being released from the Site. This part focused on improving the efficiency of the water treatment facilities and controlling the AMD discharges from the mine drainage adits. The discharges from the adits was accomplished by plugging the Reynolds and Chandler adits. The second part of the plan was aimed at reducing the AMD generated in groundwater and surface water runoff from the mine wastes. A lined and capped repository located in the mine pits for acid generating mining waste and water treatment plant sludge was found to be the most feasible alternative. Beginning in 1993, mining wastes which were the most significant sources of AMD were being excavated and placed in the Mine Pits. In November 1995, all of the waste from these sources had been excavated and placed in the the Mine Pits. This paper discusses EPA's overall approach to stabilize on-site sources sufficiently such that aquatic, agricultural, and drinking water uses in the Alamosa watershed are restored and/or maintained with minimal water treatment.