2016-10-28_PERMIT FILE - C2010089A (27)

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highwall was reclaimed. The 2nd Park Lateral continued to flow during irrigation seasons during the period that GW -N8 and GW -N9 have been monitored and groundwater mounding (seasonal irrigation water infiltration) is apparent on the hydrographs. Maximum draw down occurred in 2.75 years; however, the pit along with backfilling and reclamation will migrate at about 550 ft per year or about 1510 ft in 2.75 years. The sense is that water levels in the adjacent bedrock zones will begin to recover before maximum draw down is realized. Modeling Transient simulations were performed for the New Horizon Mine (see New Horizon #2 Area permit) for a five-year period, using the maximum drawdown estimates for the overburden and coal. These drawdown results were expressed as a maximum at the pit and are expressed as a conical depression which results in decreased drawdown at further distance from the mine. For the overburden, the pit drawdown was 5 feet for years 1 and 2, 8 feet during year 3, 15 feet during year 4, and 30 feet during year 5. The drawdown for the coal simulation was 8 feet during year 1, 5.8 feet during year 2, 6 feet during year 3, 7.3 feet during year 4, and 8 feet during year 5. The simulations for New Horizon Mine indicated that the zero impact contour for the overburden and coal after five years of mining is approximately 4,000 feet. Further, the overburden and coal drawdown contours at New Horizon Mine did not intersect any of the model boundaries, therefore, no impact of the San Miguel River from drawdown in the deeper part of the overburden or coal were predicted. However, some of these predictions do not directly correlate with actual observations made at the old Peabody Nucla Mine (New Horizon #1 Area). For instance, draw down observed at ground water monitoring hole GW -N8 (see New horizon #1 area permit) was first detected (November 1980) when the coal face was only about 760 ft from the location of GW -N8. Suggesting that at NHN Mine the zero draw down contour is much closer to the pit face than 4000 feet and the cone of depression is much steeper. Further, during the same period another ground water monitoring hole GW -N9 located only about 854 ft north of the final highwall showed no response (and has not to date) to the drainage from the old Peabody highwall. Version v.2.8.2 of MODFLOW was used to make several simulations of the expected cone of depression. These simulations utilized the hydraulic conductivity value (2.1 ft/day) that was measured at GW -N9. The MODFLOW runs (Figure 2.05.6(3)-2d and Figure 2.05.6(3)-2e) are contained in Appendix 2.05.6(3)-2 and agree well with the interpretation presented on Figure 2.05.6(3)-2c which is also contained in the Appendix 2.05.6(3)-2. Calculated average daily pit inflow for the coal and overburden zones (K value 2. 1, gradient 0.055, pit length 2217 and saturated thickness of 15 ft) is about 3840 cubic ft/day or about 20 gpm in year 1 and declining in subsequent years as the bedrock zones dry out as the result of diverting the 2nd Park Lateral water through the HDPE pipeline. As a matter of clarification, the HDPE pipeline will be moved to the approximate location of the 2nd Park Lateral after mining, backfilling and replacement of top soil has progressed far enough north. This is expected to require about 3 to 4 years after mining begins. The HDPE pipeline will be retained to prevent the irrigation water from draining into the very permeable pit backfill. This will also prevent the direct loss of irrigation water along the course of 2nd Park Lateral as occurs now. The HDPE pipeline will Section 2.05.6(3) Page 13 April 2016 (PR -01)