2014-07-11_REPORT - C1980007 - Laserfiche WebLink

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West Elk Mine 2013 Annual Hydrology Report 55 The monitoring wells with one or more parameters elevated 10 percent or more above comparable baseline maximums are discussed below. Several wells had elevated laboratory electrical conductivities (EC) in WY 2013: Upper Dry Fork Alluvial Well (632 µmhos /cm compared to the maximum baseline value of 509 µmhos /cm), SOM -80 (1,100 µmhos /cm compared to the maximum baseline value of 897 µmhos /cm), SOM -45- H2 (1,570 µmhos /cm compared to the maximum baseline value of 1,390 µmhos /cm), and 03 -11 -1 (3,210 µmhos /cm compared to the maximum baseline value of 2,730 µmhos /cm). Total iron concentrations in Well 01 -11 -1 were 1.28 mg /L compared to the baseline maximum value of 0.99 mg /L. 5.4.2 Impacts to Groundwater Quantity Routine (post- baseline) monitoring of groundwater levels in the monitoring wells is conducted three times per year, corresponding with rising limb, peak flow, and low flow periods. Groundwater level and elevation data for the monitoring wells are summarized in Appendices F and G. Mining operations appear to have impacted the groundwater levels in several wells, but levels may also have been impacted by recent drought conditions. The water level drop in the following wells may be mining related due to the up- gradient diversion of surface water runoff in the area. Wells GP -3, RPE -7, and GP -4 have been dry for multiple years and have remained dry to nearly dry through WY 2013. Wells RPE -1 and RPE -7 did not have enough water to collect a sample in WY 2013. As noted in Section 5.4, the casing in numerous wells has collapsed due to mining related subsidence. In WY 2013, the daily average water level in the Upper Dry Fork Alluvial well, measured by a data logger, ranged from a minimum of 15.50 feet btoc to a maximum of 18.48 feet btoc, compared to 14.21, and 16.67 feet btoc, respectively, in WY 2012. The water level changes in the Upper Dry Fork Alluvial Well are likely due to seasonal changes to the alluvial groundwater associated with the Dry Fork stream flows. Water levels at the Upper Dry Fork Alluvial Well are expected to again be variable in WY 2014. In WY 2013, the daily average water level in the Lower Dry Fork Alluvial well, measured by a data logger, ranged from a minimum of 8.70 feet btoc to a maximum of 14.55 feet btoc, compared to 10.13 and 16.71 feet btoc, respectively, in WY 2012. Water levels have been slowly recovering in WYs 2012 and 2013, as mining activities move away from the Dry Fork drainage. Well SOM- 45 -H -2 has been affected by the underlying longwall mining in Panel 13. This well is completed in the barren member of the Mesaverde Formation above the F Seam. The interburden between this horizon and the mined interval is about 800 feet thick. Water levels in well SOM- 45 -H -2 have recovered slowly from WY 2006 to WY 2012, but were down about 4 feet in WY 2013 from WY 2012 (Appendix F). Well SOM -76 has been dry since WY 2010 and remained dry in WY 2013, most likely as a result of mining activities. The well is expected to remain dry in WY 2014, but may recover at some point in the future, after mining has moved away from the Dry Fork drainage area. June 2014 HydroGeo, Inc.