2010-08-02_REVISION - M1977300 (27)

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Environmental Protection Plan, Schwartzwalder Mine 9-1 • 9. GROUNDWATER QUALITY (a) Existing and Potential Future Groundwater Uses One domestic water supply well exists at the mine site. The domestic well is completed in alluvium, on the northern side of Ralston Creek, and was pumped for water supply during mine operations and reclamation. When the mine is fully closed, the well will be property abandoned in accordance with state regulations, if no future uses of groundwater at the mine site after closure are anticipated. No downgradient water supply wells are completed in Ralston Creek alluvium between the project boundary and Ralston Reservoir. Because the land is owned by Jefferson County and is held as Open Space, no future uses of groundwater in the Ralston Creek alluvium are anticipated. The nearest well that accesses groundwater in weathered bedrock, shallow alluvium, and colluvium for domestic water supply is located in excess of 3,700 feet (0.7 miles) from the mine. Numerous others are located within a two-mile radius of the mine. It is anticipated that domestic use of groundwater from these wells will continue in the future. Significant increases in the number of domestic wells are not expected. (b) Groundwater Quality Data (i) Colorado Groundwater Quality Standards and Point of Compliance Colorado has developed numeric standards that apply to classified groundwater. The majority of the numeric standards are set at the maximum contaminant levels (MCLs) for public drinking water supplies, as established by the National Primary Drinking Water Regulations. The remainder are derived from the Colorado Basic Water Standards for Ground Water (5CCR 1002-41, amended October 13, 2009, effective • November 30, 2009). These human health levels are set to protect the public from acute poisoning and from long-term "chronic" effects. The classification system consists of five (5) categories based on existing and potential future uses and actual water quality data. Groundwater may be assigned more than one class because it may have more than one existing or potential use. The classes are: 1. Domestic Use - Quality 2. Agricultural Use - Quality 3. Surface Water Quality Protection 4. Potentially Usable Quality 5. Limited Use and Quality A compliance well was originally drilled at the property boundary for the alluvial groundwater. However, downgradient well MW8 is always dry and has never yielded a sample. The alluvium pinches out, and groundwater in the alluvium is forced into Ralston Creek. For nearly two decades, the creek was the point of compliance for groundwater in the alluvium, and was monitored routinely at station SW-BPL (below the property line). A new monitoring well (MW12, located approximately 450 feet upgradient of the property boundary) was drilled in November 2008, and a replacement well (located closer to the property boundary) is under consideration. • 4109C.100731 Whetstone Associates