2014-05-12_PERMIT FILE - C2010089 (3)

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wells are shown on Map 2.04.7 -1. New ground water monitor well GW -N56 will monitor the underburden (UB), well GW -N57 will monitor the coal zone (Coal) and well GW -N58 will monitor the overburden. GW -N56 was completed on August 8, 2012 while GW's N57 and N58 were completed on August 9, 2012. The completion diagrams for the three new monitor wells are shown on Figure 3 of Appendix 2.04.7 -1. These wells will be monitored and reported on the same cycle as the other ground water monitoring wells. It is anticipated that these wells will become the points of compliance after review of additional data and consultation with DRMS. Alluvial Water Level The drainages developed within the NHN permit area are developed on the weathered dip slope of the northeast limb of the Nucla Syncline. Map 2.04.6 -2 (the LDx Structure Contour Map) shows the structure of the NHN permit area. The primary drainage is Meehan Draw which is developed on bedrock. No alluvial wells were installed due to the lack of alluvium. Overburden Water Levels Water levels at the three overburden monitoring wells GW -N49, GW -N52 and GW -N55 (see completion diagrams, tabulated data and hydrographs in Appendix 2.04.7 -1) have been monitored monthly since October 10, 2008. Two of these wells (GW -N49 and GW -N52) show the seasonal fluctuation resulting from the seasonal irrigation. Monitoring well GW -N55 is essentially dry showing a slight increase in water level since completion but without even enough water to collect samples. This suggests that two conditions exist in the overburden zone: (1) vertical permeability of the unweathered overburden below the zone of weathering is low and (2) the lateral permeability is also low as the unweathered overburden is not reflecting up dip recharge from the 2nd Park Lateral. The amplitude of the seasonal fluctuation at GW -N49 is about 12 feet whereas the annual fluctuation at GW -N52 is over 19 feet. Map 2.04.7 -2 and Map 2.04.7 -3, respectively show the potentiometric surfaces and direction of flow of the overburden zone at both the lowest level (winter conditions, no irrigation flow) and highest level (summer conditions with full irrigation). The gradient of the potentiometric surface varies from about 0.023 ft/ft to about 0.044 ft/ft during the seasonal low levels and 0.033 ft/ft and 0.05 ft/ft during seasonal high levels. The area directly north of the old Peabody highwall has a low seasonal gradient of 0.022 ft/ft and a gradient during the irrigation season of 0.082. The difference in gradients from summer to winter further demonstrates the ground water mounding effects of the recharge from irrigation. The hydrograph from monitoring well GW -N8 (monitoring suspended) shows the response in 1983 to mining at Peabody's Nucla Mine (see GW -N8 hydrograph in the Appendix 2.04.7 -1 of this section.). Dakota Coal Water Levels All three of the coal zone monitoring wells (GW -N48, GW -N51, and GW -N54) demonstrate the seasonal fluctuations in water levels resulting from irrigation (see Appendix 2.04.7 -1 of this application). Comparing the coal zone hydrographs with the overburden zone hydrographs indicates that the lateral permeability of the coal zone is higher than that of the unweathered overburden. The response to the start of spring irrigation at well GW -N54 is about a month later than at wells GW -N48 and GW -N51 suggesting that rise in water level at that well is due to up dip recharge. This further suggests that the coal zone at this monitoring well is relatively well confined and isolated from the overburden zone and the underburden zone. Well GW -N54 has about 10 feet of artesian head during the summer months. The amplitude of the seasonal fluctuation due to irrigation is about 12 feet, 19 feet, and 9 feet for wells GW -N48, GW -N51 and GW -N54, respectively. Map 2.04.7 -4 and Map 2.04.7 -5, respectively shows the potentiometric surfaces and direction of flow of the coal zone at both the Section 2.04.7 Page 3 October 2013 (TR -05) N: \WFC \2013 \NHN \DRMS Permit Revisions \TR -05 \2.04.7 Hydrology Description_TR- 05.dou