2011-03-14_REVISION - M1977493 (44)

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CM0001998 • Ground Water Quality Tenmile Creek valley Ground water quality in the Tenmile Creek valley is monitored by two ground water monitoring wells, GWM #1 and GWM #2, which were installed in 1987 below the Mayflower Tailings Dam. Figure 1 shows the monitoring well locations. Both wells were completed in the alluvial and glacial soils. Appendix A presents a drillers' and completion log for each well. Water quality sampling activities at GWM #1 and GWM #2, have been conducted on a quarterly basis since June 1987. In development of the Climax Ground Water Monitoring Plan, the last five ground water quarterly sampling events were statistically evaluated to determine current ground water conditions in the Tenmile Creek valley. Historical sampling for the two wells was also evaluated. A summary of the last five quarterly sampling events is presented in Table 2. Historical ground water quality data are presented in Appendix B and is part of public record as the data from these wells are part of the Climax CPDES permit. For comparison, the Colorado Basic Ground Water Standards have also been included in the Table 2. As indicated by the statistical evaluations, all primary constituents were within the Colorado Basic Ground Water Standards (CBGS) for the quarterly sampling activities at GWM #1 and GWM #2. Evaluation of the historical sampling results since 1987 (Appendix B) indicate elevated levels of cadmium and manganese in GWM #1. Manganese concentrations have not exceeded CBGS since 1988 and have not been detected during the past five quarterly sampling periods. In addition, cadmium concentrations have not exceeded the Colorado • standards since September of 1991. GWM #2, located downstream of GWM #1, has not exceeded CBGS since sampling began in June 1987. Arkansas River Valley The ground water quality in the Arkansas River Valley is monitored by well AMW (Figure 1). This well was installed in September of 1993. A drillers' and completion log for this well is presented in Appendix A. The AMW was completed in alluvium and is therefore representative of alluvial ground water conditions in the valley. The ground water in the Arkansas River Valley is forced to the surface and reports the Arkansas River downgradient of AMW. Water quality samples have been collected at AMW on a quarterly basis since late 1993. Samples from the AMW were also collected on a monthly basis beginning in June 1993 and ending October 1994. The analytical sampling results from the quarterly sampling at AMW are summarized and presented in Table 3. The water quality data are presented in Appendix B. As shown in Table 3, the water quality at the AMW demonstrates low to non-detectable concentrations of primary constituents, with the exception of manganese. The manganese concentrations, however, have decreased over the last five quarterly sampling events, from 1.32 mg/l to 0.43 mg/I. This trend is considered to be related to well location or completion.