2020-06-04_PERMIT FILE - C1981008A (2)

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GW-NIP1 and GW -N6. These wells have displayed a slight shallowing trend with time. There were no distinguishable effects from the mining operation at New Horizon 1 area or recharge from precipitation events on the underburden aquifer system. Spoil Water Levels Four wells (GW -N10, GW -N26, GW -N27 and GW -N28) were installed to monitor water levels in the spoil aquifer at the New Horizon 1 area. Map 2.04.7-1A shows the spoil well locations. Monthly water level data including hydrographs are contained in Attachment 2.04.7-6 (formerly Peabody Appendix 7-1). The spoils aquifer is dry or nearly dry except for the area in the vicinity of GW -N27. At this location the spoil aquifer has approximately 6.4 feet of saturation. This well was installed in August of 1987. In general, this well has shown seasonal fluctuation in the water level to correspond with the irrigation ditch flow. Multiple Completion Well Water Levels Five wells with multiple seam completions have been installed at the New Horizon 1 area (Map 2.04.7-1A). Monitor Wells GW -N8 and GW -N9 were installed in the overburden and the Dakota coal aquifers northwest of the New Horizon 1. Monitor Wells GW -N23, GW -N24 and GW -N25 were located in what had been referred to as the scraper area in the southeastern portion of the permit area. Those monitor wells were completed in early June, 1986 in the overburden, Dakota coal and underburden aquifers. Water level information indicates that the scraper area wells are dry. Water level information has been gathered for wells GW -N8 and GW -N9 on a monthly basis since September, 1979. Well GW -N8 is located up gradient and adjacent to the mine pit. As a result, a 13 foot drawdown in static water level occurred prior to 1983. Since mining ceased in late 1983, the static water level has begun to recover. Both wells GW -N8 and GW -N9 show seasonal fluctuations in water levels as a result of recharge from the ditch irrigation system. There is no evidence of any discernible responses to precipitation events at these wells. There are no single aquifer (overburden or Dakota coal) wells completed in the northwest portion of the New Horizon 1 permit area. Consequently, wells GW -N8 and GW -N9 have been incorporated and used in both the overburden and Dakota coal potentiometric surface maps (Maps 2.04.7-2 and 2.04.7-3). Potentiometric Surfaces Potentiometric surface maps for the overburden, Dakota coal and underburden aquifers are presented in Maps 2.04.7-2 and 2.04.7-3, respectively. Overburden The potentiometric surface map of the overburden is presented on Map 2.04.7-2. The water level contours were constructed based on the static water level measurements made in September, 1987 from five overburden wells and two multiple completion (overburden and Dakota coal) wells. It was necessary to include the two multiple completion wells (GW -N8 and GW -N9) in the overburden potentiometric map because they are the only monitor wells located in the northwest portion of the permit area. The overburden generally has the shallowest static water level of the bedrock aquifers that are monitored within the study area, so the multiple completion wells should be representative of the overburden aquifer water levels. Ground water in the overburden aquifer is generally unconfining to only slightly confining. The flow in the overburden is generally from the northeast to the southwest and is topographically controlled. Potentiometric contours indicate that there is discharge of ground water along Tuttle and Calamity Draws. The ridge that separates the two draws is a ground water divide, causing the ground water to flow from the Page 2.04.7-6 March 2017 (TR -77)