2019-10-25_PERMIT FILE - C2010089

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Dakota Coal Water Levels All coal zone monitoring wells (GW -N51 and GW -N54), demonstrate 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 overburden. The response to the start of spring irrigation at well GW -N54 is about a month later than at well 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 (below the lowest coal seam to be mined) 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 19 feet and 9 feet for wells 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 lowest level (winter conditions, no irrigation flow) and highest level (summer conditions with full irrigation). The gradient of the potentiometric surface varies from about 0.029 ft/ft to about 0.047 ft/ft during the seasonal low levels and 0.033 ft/ft and 0.051 ft/ft during seasonal high levels. The area directly north of the old Peabody highwall has a low seasonal gradient of 0.028 ft/ft and a gradient during the irrigation season of 0.079 ft/ft. Underburden Water Levels One of the three underburden zone monitoring wells (GW -N50) that have been monitored since October 2008 clearly shows the seasonal effects of surface irrigation (see Appendix 2.04.7-1 for hydrographs). Similar to the overburden at well GW -N55, GW -N53 indicates very little if any response to surface irrigation. GW -N53 produced negligible water during drilling and the recovery from the first water level measurement to the second measurement attests to the low rate of water level recovery at this location. As with the GW -N55 well at this site, the GW -N53 monitoring well shows that the rates of vertical and lateral recharge of the underburden is low. Map 2.04.7-6 and Map 2.04.7-7, respectively shows the potentiometric surfaces and the direction of flow of the underburden zone at both the lowest level (winter conditions, no irrigation flow) and highest level (summer conditions with full irrigation). The amplitude of the seasonal fluctuation due to irrigation is about 23 feet for well GW -N50. The gradient of the potentiometric surface varies from about 0.029 ft/ft to about 0.046 ft/ft during the seasonal low levels and 0.0396 ft/ft and 0.055 ft/ft during seasonal high levels. The area directly north of the old Peabody highwall has a low seasonal gradient of 0.024 ft/ft and a gradient during the irrigation season of 0.08 ft/ft. The underburden zone artesian head at GW - N50 varies from about 15 feet to about 39 feet above the zone from winter to summer. Backfill Water Levels The NHN permit area encompasses part of the area of the old Peabody Nucla Mine, which ceased production in 1983. Overburden backfill material exists south of the old Peabody high -wall. Four wells (GW -N10, GW -N26, GW -N27 and GW -N28) monitored water levels in this backfill material through the end of 1987. All four of these wells were abandoned and reclaimed in November of 2001. Map 2.04.7-1 shows these backfill monitor well Section 2.04.7 Page 4 March 2018 (TR -16)