2018-07-02_PERMIT FILE - C2010089A (19)

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level from October '08 through March of 2009 at which point they rapidly recover again. This demonstrates the effect that the seasonal surface irrigation has on the groundwater zones. The water levels decline in the fall and winter after the irrigation water is shut off in the 642nd Park Lateral" and rapidly recover in the spring when the irrigation flow resumes. The hydrograph for GW -N9 (contained in the New Horizon 1 Permit and in the Appendix 2.04.7-1 of this Section) demonstrates this annual cycle from September 1979 through December of 1987. Three (3) more groundwater monitoring wells were installed in the southwestern portion of the NHN permit area. The locations of these three wells are shown on Map 2.04.7-1. Groundwater monitoring 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. The completion diagrams for the three 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 groundwater monitoring wells. After review of additional data and consultation with DRMS, groundwater monitoring wells GW -N56, GW -N57, and GW -N58 have been designated as points of compliance. Alluvial Water Level 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 (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 lack of alluvium. Overburden Water Levels Water levels at the overburden monitoring wells GW -N52 and GW - N55 have been monitored monthly since October 2008. One of these wells (GW -N52) shows 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 overburden below the zone of weathering is low and (2) the lateral permeability is also low as the overburden is not reflecting up dip recharge from the 2nd Park Lateral. The amplitude of the seasonal 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 ft/ft. The difference in gradients from summer to winter further demonstrates the groundwater mounding effects of the recharge from irrigation. The hydrograph from monitoring well GW -N8 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). Section 2.04.7 Page 3 March 2018