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West Elk Mine 2006 Annual Hydrology Report 39 <br />4.7 Underground Thermal Event <br />1'he West Elk Mine was evacuated. on October 27, 2005 after elevated. levels of carbon monoxide, <br />hydrogen, and ethylene were detected. The source of the elevated gas levels was from a. <br />spontaneous combustion thermal event (Thermal Event) in the lon~rw~all 24 panel area. MSHA was <br />notified of the 'Thermal Event and issued a 103K order that required MCC to secure SSl_lA <br />approval of all. underground and other related activities related to the thermal event area (MCC, <br />2007). T'he "Thermal Event was controlled. in early 2006 and normal mining operations of the E <br />Seam began. late January 2006 and B Seam. mining started in early March 2006. <br />In November through December 2005 MCC pumped water directly out of the North Fork of the <br />Gunnison to the Thermal F..,vent. The pumping rate was approximately 3,000 gpm until the water <br />pipeline froze in late December (MCC, 2007). The total volume pumped during the Thermal Event. <br />was estimated to be 404.35 ac-ft (MCC, 2007). <br />4.8 Biomonitoring Testing for Toxicity <br />During WY 2006, MCC conducted Biomonitoring tests as required by the CPDS permit (MCC, <br />2007). Biomonitoring samples were collected quarterly from the West Fork of the Sylvester Gulch <br />effluent discharge (outfall 017). Testing included whole effluent toxicity or "WET" tests. Static <br />toxicity tests for acute (48-hour) and chronic (96 hour) were completed in WY 2006. The test <br />organisms included the daphnid (Daphnia magna) and the fathead minnow (Pimephales promelas). <br />The test results indicated that the effluent from outfall 017 was acutely toxic to daphnid in the 15`, <br />and 2"d quarters of 2006 as detailed in the quarterly Discharge Monitoring Report (DMR) <br />submittals. MCC established that high alkalinity is the cause of the daphnid mortality. <br />5.0 ASSESSMENT OF MINE-INDUCED HYDROLOGIC IMPACTS AND -. <br />ANTICIPATED IMPACTS IN WY 2006 <br />5.1 Surface Water <br />MCC maintains a network of 23 stream flow gauging stations throughout the permit and lease areas <br />(Table 2). The locations of the surface water monitoring stations are shown on Map 2. Daily mean <br />flow summary tables are presented in Appendix A. Surface water flow hydrographs are presented <br />in Appendix B and the field and laboratory surface water quality data are presented in Appendix C. <br />December 2007 HydroGeo, Inc. <br />