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Mountain Coa! Company 2000 Annual Hydrology Report West Elk Mine C~ Groundwater Impacts The groundwater monitoring system at the West Elk Mine is shown on Map 2 and summarized in Table 4. Table 5 shows the completion information for the eighteen wells that aze currently monitored at the West Elk Mine by the formation in which they were completed. These formations include: the alluvium and colluvium (unconsolidated materials), the Barren Member of the Mesa Verde, the F-Seam, the E-Seam, and the B-Seam. Graphical representations of the historic water levels observed at these monitoring wells are showm in Appendix F. Water level and quality data obtained in WY00 for each of the monitoring wells can be found in tabular form in Appendix G. GP-3 and GP-4, the two colluvial wells in the mine facilities area, showed water level drops of up to four feet. The decrease in the water surface elevation may have been related to decreased seepage as a result of the lining of ponds MB-1 and MB-2R. Mining in longwall panel 10 during WY98 appears to have had a minor effect on well SOM-80, completed in the Barren Member. In WY00, water levels dropped an additional three feet below the historic elevation. Wells SOM-45-H-1 and SOM-45-H-2 appear to have been affected by longwall mining in panel 13-A during WY00. Although the wells are completed in the Barren Member, the overburden thickness is only about 800 feet. Continued monitoring may indicate whether the water levels will stabilize. • The casing for well SOM-2-H, completed in the F-Seam, appears to have been damaged. Field monitoring encountered a pinched casing approximately 540 feet below the surface. While the water level had been decreasing over the past view years, the well no longer appears to be providing useful information. Well SOM-16-H also appears to have experienced damage to the well casing, and water samples are no longer able to be retrieved from this well. As discussed in the last AHR, mining activities in WY99 appear to have affected the water level in well RAV-4b, which is completed in the B-Seam near the Box Canyon Mains, by encountering the Oliver No. 2 fault zone. Encountering the fault zone inflows in the Box Canyon Mains likely reduced the water pressure in the fractures and the water level in RAV-46 is likely equilibrating near the elevation where the fault was encountered. The water level in RAV-4b continued to drop before rebounding slightly in WY00. However, there is no practical significance to the impact since the B-Seam is not used as a water source and the extent of the impact is likely confined to the vicinity of the mining. Also, well RAV-4b is completed within one of the planned longwall panels and will likely be destroyed by longwall mining. None of the other wells in the monitoring program showed indications of impacts that could be related to mining during WY00. In addition, the water quality data collected during WY00 did not show any anomalous values that would indicate mining impacts. 83l -03?.550 Page 25 Wright Water Engineers