2012-10-01_REVISION - M1977310 (10)

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JD -6 Mine Environmental Protection Plan 40 9.5 Groundwater Quality No monitoring wells exist on the JD -6 lease, and therefore no site - specific water quality information is available. Water quality in the vadose zone from the lysimeter is presented in Section 9.6. The following information applies to groundwater quality in the region. 9.5.1 Alluvial Groundwater Quality Alluvial groundwater, where it occurs, is a calcium sulfate or calcium bicarbonate type water, with sodium concentrations of 130 mg /L or less (Weir, et al., 1983). Total dissolved solids in the alluvium of the Paradox Basin range from 302 to 1,560 mg /L, with an average of 770 mg /L (Weir, et al., 1983). These concentrations exceed Secondary Maximum Contaminant Levels (SMCLs) established for drinking water. 9.5.2 Upper Aquifer (Mesozoic) Water Quality Weir, et al., (1983) reported that the upper Mesozoic aquifer is typically a calcium bicarbonate water containing varying concentrations of sulfate and that "water from units containing abundant shale, such as the Mesaverde Group, Mancos Shale, and Brushy Basin Member of the Morrison Formation is typically a sodium bicarbonate water containing sulfate or chloride." The range of dissolved solids reported by Weir, et al. (1983) for the Morrison Formation was 1,260 to 4,040 mg /L with sulfate ranging from 310 to 1,200 mg /L. These TDS and sulfate values naturally exceed SMCLs for drinking water. 9.6 Lysimeter Monitoring Results Lysimeter monitoring has been conducted at the JD -6 Mine since 2007. The suction lysimeter is located below the toe of the waste rock pile (Figure 10) and was installed to a depth of 22 feet below ground surface in January, 2007. The suction lysimeter is equipped with a Soilmoisture® pressure- vacuum Soil Water Sampler model 1920F1 /K1, which uses a porous water cup to obtain soil water samples from both saturated and unsaturated soils at depth. The sampler is designed to remove any available water from the soil by creating a vacuum inside the sampler that is greater than the soil suction, which creates a gradient which draws water into the ceramic cup. The purpose of lysimeter monitoring at the JD -6 Mine is to provide data on whether any localized water exists in the subsurface of the waste rock and the underlying soils, and to identify whether any potential flowpaths exist. The secondary use of the lysimeter is as an early detection system for any potential migration of constituents from the waste rock pile in the future. The lysimeter was sampled monthly from 2007 through 2010, with few exceptions, and quarterly beginning in 2011. The lysimeter was dry during 92% of the sampling events (46 of 50 events), indicating that groundwater seepage below the waste rock pile is limited. The lysimeter contained a small volume of water during three sampling events in the spring and summer of 2008, which was an exceptionally wet summer (Section 7.2) and again in December 2012 (Table 22). The limited seepage is consistent with the climactic data and hydrogeologic conceptual model of the site (Sections 7.2, 7.6, and 5.4.2) which indicate that evapotranspiration often exceeds infiltration in the area. The waste rock pile will be recontoured and revegetated during final reclamation, which will further reduce the potential for infiltration through the waste rock pile. 4148A.120927 Whetstone Associates