2010-12-17_REVISION - C1981019 (153)

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Groundwater 47 The bedrock monitoring wells were installed in September and November 2004 in five locations. Groups of monitoring wells were located upgradient (MWC -04 -29 cluster), downgradient (MWC -04 -1 and MWC -04 -13 clusters) and on the edges of the proposed Collom Mine (MWC -04 -05 and MWC -03 -33 clusters). Wells at the periphery of the proposed mine were located so they could be used before, during, and after mining. Bedrock monitoring wells were screened across specific coal and sandstone units of the Williams Fork Formation that were deemed most likely to contribute to groundwater flow to the pit. These included the F sandstone, F/G coals, and the H and I sandstones. Although the H and I sandstones are discontinuous and below the planned bottom of the proposed pit, groundwater conditions were evaluated because the H and I sandstones may need to be dewatered to reduce excessive pore pressure beneath the pit floor. The screened intervals of the wells were determined from the geologic information collected during the exploration program (described in Section 2.2.1) and additional geophysical logs run on the well boreholes. These data were reviewed by the on -site geologist with assistance of the Collom Geologic Team to identify the targeted hydrogeologic zones and appropriate screened intervals. To collect depth - specific data at each location, wells were installed in clusters of two or three. All wells were installed according to the protocols described in the Work Plan (WMC, 2004) (Appendix 1.A). All bedrock monitoring wells were installed in 7.875 -inch diameter holes drilled using standard rotary methods with air /foam or water as the circulation fluid. The wells were completed with Certa -IokTM SDR -17, 4.5 -inch diameter, PVC casing and screen. Wells were developed with a submersible pump in accordance with the WMC SAP (Appendix 13). Details of the well completions are provided in Table 5.2. Well completion logs are provided in Appendix 5.A. Table 5.2 also includes well UL- 95 -01, which is a historic well completed in the Fab seam that was to be used for baseline monitoring. A comparison of the screened intervals of the bedrock monitoring wells to the final "down- the - hole" logs (Appendix 5.A) indicates that two of the wells were screened above their target intervals. These include MWC -04 -01 H and MWC- 04 -33H, which were targeted for the H sandstone, but were screened in sandstones within the lower part of the G sequence, above the Gc coal seam. This resulted from the re- interpretation of the logs by KEC. Five shallow monitoring wells (MC- 04 -01, MC- 04 -02, MS- 04 -01, MS- 04 -02, and MI-C-04-01) were installed in Collom, Straight, and Little Collom Gulches in August 2004 to complement the three existing valley fill monitoring wells (MJ- 95 -01, MJ -95 -02 and MJ- 95 -03). Locations of all valley fill wells are shown on Figure 5.6 and Plan 5.1. • 2572 -R2 Colowyo Coal Company Water Management Consultants