2012-09-28_REVISION - M1977307 (28)

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The following sections of this report provide a site description of the mining activities and the associated hydrologic conditions, a description of the numerical model used to simulated groundwater and contaminant transport, and a discussion of the results and environmental impacts of mining operations on the groundwater and surface water systems. All work was conducted under the direction of the Cotter Corporation. 2.0 Site Description 3 SM -18 Mine Report GeoScience Services The SM -18 mine is located east of the former town of Uravan on the valley walls approximately 400 feet above the San Miguel River. The waste rock area adjacent to the mine is approximately 1800 feet from the river. According to the geologic map (McKay, 1955), the waste rock is located approximately at the contact between the Brushy Basin and Salt Wash Members of the Morrison Formation (Figure 1). Approximately 270 feet of Salt Wash interbedded sands and mudstones underlie the site with another120 feet of Summerville mudstones and 120 feet of Entrada Sandstone. In the San Miguel River valley, the upper portion of the Entrada Sandstone has been eroded and replaced by river alluvium. The geologic structure shows that the rock layers in the vicinity of the mine dip to the northeast or away from the river. For modeling simulations, however, it was assumed that the larger structural feature of the southwest dip from the Uncompahgre uplift has generated sufficient regional elevation that hydraulic pressures in the Entrada aquifer result in groundwater flow toward the San Miguel River. Consequently, modeling simulations discussed in subsequent sections assume downward movement of constituents of concern from the waste rock through the unsaturated Salt Wash Member and the Summerville Formation with horizontal movement via groundwater flow in the Entrada Sandstone and river alluvium that eventually discharge into the San Miguel River.