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Christy Woodward <br />September 17, 2008 <br />Page 4 <br />aquifer, which overlies deeper aquifers that are isolated from the Top Rim sandstone by the <br />Summerville Shale. <br />Development Rock Areas <br />Figure 3 presents an interpretive cross-section of Big Gypsum Valley showing the location of <br />the Development Rock Areas (DRAs) as well as a major salt unit in the area. The location of <br />the water table is uncertain and is projected based on the depth to groundwater observed <br />within the West Sunday underground workings. A groundwater diN,ide is interpreted to be <br />present between the underground workings and the DRAB. <br />Two features of the interpretative cross-section are important with respect to the potential for <br />development rock to affect groundwater quality. Firstly, the DRAs are underlain by the <br />Brushy Basin Member of the Morrison Formation, which consists of approximately 200 to 300 <br />feet of shale. This confining unit overlies the Salt Nash aquifer. Therefore, the shale of the <br />Brushy Basin Member would be expected to restrict downward migration of potential <br />constituents that could be dissolved from the development rock:, and the high clay content of <br />this rock unit may provide natural attenuation capacity for these constituents. Secondly, the <br />groundwater table is in close proximih, to the major salt unit within Big Gypsum Valley. <br />Therefore, it is possible that the quality of groundwater in this area is poor (e.g. high TDS <br />concentrations) as a result of natural conditions. The ambient water quality affects potential <br />future uses of the groundwater as well as the rcgulatory- requirements applicable to it <br />(Colorado Water Quality Control Commission [WQCC] Reg ilation §41.4). <br />Pertinent Groundwater-Related Issues <br />Observations of small quantities of groundwater within the underground workings and the <br />presence of DRAs with potential to affect grounds vater support evaluation of groundwater- <br />related issues that are pertinent to protection gf the environment and compliance with <br />requirements of the Hard [pock Metal Mining Rules (HRMMRs). These pertinent issues <br />include: <br />1. What is the ambient groundwater quality? <br />2. What is the direction and rate of groundwater flow? <br />3. What is the potential effect of underground mining operations on groundwater quality? <br />4. What is the persistence of any effects downgradient from underground mine workings? <br />s. What is the potential for DRAB to affect groundwater quality? <br />This work plan addresses issues 1 through 4. The 5th issue, the potenti al for DRAs to affect <br />groundwater quality, is addressed primarily by a second work plan, which focuses on <br />assessing the geochemical characteristics of rock stored within the DRAs. However, the