2016-01-07_PERMIT FILE - C2010089A (3)

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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 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. Underburden Water Levels Two (GW -N47 and GW -N50) of the three under burden zone monitoring wells that have been monitored since October 10, 2008 clearly show the seasonal effects of surface irrigation (see Appendix 2.04.7-1 for hydrographs). Similar to the unweathered overburden at well GW -N55, GW -N53 shows very little if any response to surface irrigation. This well 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 overburden monitor well at this site the GW -N53 monitoring well shows that the rates of vertical and lateral recharge of the under burden 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 under burden 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 7 feet and 23 feet for wells GW -N47 and GW -N50, respectively. 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. The under burden zone at GW -N47 has an artesian head varying from 34 to 40 ft above the zone from Section 2.04.7 Page 4 Sept. 2015 (TR -11)