2018-11-05_GENERAL DOCUMENTS - C1981044

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Williams Fork Mines Prepared by: R. Reilley M.S. GISP C1981044 5 November 2018 24 of the E coal seam is above the current water level in the No. 5 Mine well. Monitoring of the well was suspended in 2001 through 2005 as part of the temporary cessation monitoring plan. Since monitoring was resumed in 2006 to July of 2013, the water level has remained relatively stable. As indicated above, the No. 5 Mine pump was turned off in July of 2013; no further pumping at this site is anticipated in the near future. Historical field conductivity data for the Trout Creek Sandstone wells indicate no adverse water quality impacts related to mining. The conductivity levels appear elevated to the levels observed in the 80’s. This may be related to consistent pumping at the site. MCM must continue to monitor this trend at the No. 5 mine well. Middle Sandstone - Outlying Wells The most significant hydrologic impact caused by Mines 5 and 6 may be an approximate 60-foot drawdown of ground water in the Middle Sandstone as observed in wells TR-4, TR-7a, 81-01 and 83-03. Water elevation in wells 83-01 and 83-02 are above baseline water levels. This drawdown persisted as recently as 2013, which is the most recent reporting year, although the water levels have stabilized. This drawdown is comparable to the worst-case drawdown projected for the overlying Twentymile Sandstone at a one-mile radius. The water level in the Middle Sandstone well farthest from the mine workings, 83-03, dropped 50 ft. from 1985 to 1997 and then began a gradual recovery until 2001 when the mine went into temporary cessation. Since 2006, the water level at this well dropped by about 25 feet and began to recover in 2011 and has since been rising. Section 2.04.7 of the permit describes the pre-mine characteristics of the bedrock aquifers and indicated that the Middle Sandstone aquifer often exceeds the primary and secondary EPA drinking water standards for boron, chromium, dissolved solids, fluoride, iron lead, manganese, sulfate and selenium. The 2013 water quality data indicated elevated conductivity levels of this aquifer and will continue to be monitored by MCM. Overall, the trends in water levels and the water quality indicate mining has not adversely impacted the Middle Sandstone aquifer outside the permit boundary. Twentymile Sandstone Water level monitoring data reported through the 2013 annual hydrology report had shown no substantial change in the piezometric levels in the Twentymile Sandstone that could be attributable to mining activities. The water quality data for the two Twentymile Sandstone wells, No. 9 Mine Well and Well 259, showed no adverse impact has likely occurred. Williams Fork Alluvium Ground water levels in the alluvium have remained fairly regular, with normal seasonal fluctuations apparently related to changes in river levels. Ground water levels in the alluvium are plotted in Figure 22 in Section 2.04.7 of the permit application package. Annual hydrology reports through 2017 indicate no depletion has occurred and suggest that mining appears to not have affected Williams Fork River alluvial water quality.