2012-01-23_APPLICATION CORRESPONDENCE - C2010088 (3)

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the acid sludge landfill was selected as a fourth monitoring well. This monitoring well, RW -2, is located northeast of the acid sludge landfill. See Map 8, Hydrologic Monitoring Location Map, in the PAP for the location of the monitoring wells. Two of the alluvial wells are located within the permit boundary, RW -1 and RW -2. RW -2 is located in the northeast corner of the permit area. RW -1 is located in the central portion of the permit area east of Reed Wash. RW -3 and RW -4 are both located south of the permit boundary and east of Reed Wash. RW -3 is near Reed Wash. RW -4 is located approximately 1,800 feet east of Reed Gulch. A typical completion diagram along with a summary table of specific completion information for each monitoring well is located in Volume I, Exhibit 3 of the PAP. The As -Built Drawings from 1981 when the wells were drilled and completed are provided in Volume I, Exhibit 14, Appendix B. The number designations for the monitoring wells now being utilized have changed somewhat since they were originally installed. The typical completion diagram in Exhibit 3 provides the most current and best available information for the four active monitoring wells RW -1 through RW -4. CAM collected baseline groundwater quality data during all four quarters of 2010. These data are also provided in Exhibit 3 of the PAP. Ground water was encountered by the four monitoring wells in the saturated alluvial material overlying the low permeability Mancos Shale. The depth to water in the four wells is currently either in the lowest portion of the silty clay layer or within the alluvium (ranging from about 11 to 20 feet). Ground water elevations, as measured in the four monitoring wells in June 2010, indicate the ground water flow direction is from northeast to southwest towards the Colorado River with a shallow gradient of approximately .003. The approximate elevation of the Colorado River is 4440 to 4441 feet above MSL, compared to ground water elevations of (RW -2) 4461 at the north end of the property to (RW -3) 4448 at the south end of the property. Given that the ground water flow direction is towards the river from the, upland areas to the north and the river is several feet lower in elevation than the June ground water elevations, it is unlikely that the ground water beneath the proposed loadout facility is directly related to the Colorado River. It is possible that ground water beneath the property may, in part, be the result of irrigation in the upland areas, using water from up river diversions. The water quality of the alluvial ground water beneath the property indicates that the alluvial ground water originated in the Mancos Shale or at least traveled through the Mancos Shale. The alluvial ground water quality is typical of ground water quality of marine shales in western Colorado. Total dissolved solids (TDS) range from 5,800 to 8,800 mg/L, with an average of 7,300 mg/L for the four monitoring wells. The water is predominantly a calcium- sodium sulfate water with elevated levels of dissolved manganese and iron. When compared to Regulation No. 41, The Basic Standards For Groundwater all four monitoring wells had exceedances of the Table 2 Domestic Water Supply Drinking Water Standards and Table 3 Agricultural Standards for dissolved manganese and two of the wells R2 and R4 had exceedances in the second quarter of the Domestic Water Supply Drinking Water Standards for dissolved iron. Samples from one well (R2) exceeded the Agricultural Standard for selenium all four quarters. For TDS comparison, the Colorado River upstream and downstream of the property had total dissolved solids of about 600 mg/L in June 2010 whereas the groundwater data from the monitoring wells show much higher levels averaging 7,300 mg/L. Detailed water quality information is presented in Volume I, Exhibit 3. 14