2016-01-07_PERMIT FILE - C2010089A (11)

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long. The low flow rates average about 17 gpm and represent no irrigation for about 200 days per year. The average annual flow rate is therefore on the order of about 28 gpm or about 5390 ft3/day. This flow rate compares well with the flow rate of about 27 gpm calculated by subtracting the flow in Nygren Draw (SW -N6) from the flow rate at NPDES 001, (see Table 2.04.7-5 in Section 2.04.7). This further suggests that once the irrigation water is diverted into the HDPE pipeline that highwall seepage should be more on the order of about 17gpm (< 3300 ft'/day) and then decrease as the bedrock zones dry out. The bedrock zones are tight, with low transmissivity (measured OB and Coal Zone transmissivity and hydraulic conductivity at 58 ft2/day and 2.1 ft/day respectively at GW -N9) which results in limited but steep cones of depression. The old Peabody Nucla Mine (New Horizon #1 Area) is again instructive as the hydrograph of GW -N8 (see pg. 7-1-75 of New Horizon 1 Mine Area Permit) shows the water level was first affected by the mining in November 1980. At that time the coal face was about 760 ft from hole GW -N8. Total draw down at GW -N8 after 2 years and 9 months was 12.24 ft. Monitor hole GW -N9 at a distance of 854 ft from the final high -wall has never been affected, (see GW -N8 and GW -N9 hydrographs in Appendix 2.05.6(3)-2; Figures 2.05.6(3)-2a and 2.05.6(3)-2b). Based on the evaluation of these observations, water level drawdown in the bedrock zones is expected to only extend about 590 feet beyond the permit boundary. WFC's hydrologic consultant, Bishop -Brogden Associates, Inc. (BBA), prepared Figures 2.05.6(3)-2f and 2.05.6(3)-2g in order to illustrate the observations at GW's N8 and N9. These two figures are contained in Appendix 2.05.6(3)-2. Figure 2.05.6(3)- 2c in Appendix 2.05.6(3)-2, is an illustration of the projected draw down from an ideal pit in a stationary position based on the evaluation of the GW -8 and GW -9 hydrographs. Water level measurements were suspended at GW's-N8 and N9 from 1987 through 2007 and the "old" highwall was reclaimed in 1992. Water level monitoring at these two holes was resumed during 2008 and 2009 as part of the 2 year "close out" monitoring for New Horizon #1 Area Permit. Water levels in GW -N8 have recovered about 80% of the maximum draw down since the 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, Section 2.05.6(3) Page 13 Sept. 2015 (TR -11)