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

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safe working environment in the active mining area. An opening was cut into the "buckwall" at the location of the center pit ramp to allow access from the surface into the boxcut. This notch will allow for hydraulic flow between the NHN backfill and the old backfill through the boxcut as depicted on Figure 2.05.6(3)-1. Therefore, the Probable Hydrologic Consequences should not be affected by the presence of the "buckwall". Probable impacts and therefore probable hydrologic consequences have been identified (see Attachment 2.05.6(3)-2 of the New Horizon 1 Mine Permit). A summary of the hydrologic consequences is presented in Appendix 2.05.6(3)-2 of this section of the application as Table 2.05.6(3)-2a. This table incorporates new findings with the findings from both the New Horizon #1 and #2 mine permits. These probable impacts were either determined to have no short or long term significance, or a plan has been presented to mitigate those impacts determined to have significance. Potential impacts to the hydrologic balance and the likelihood that these impacts will occur are given below. 1) Interruption of Groundwater Flow and Drawdown. The bedrock zones, overburden and coal, will be exposed or daylighted by the NHN excavation. There are no users or beneficial uses for the relatively small amount of ground water that is currently moving through the bedrock zones toward the cropline to the southwest. Recharge from irrigation (the major source of recharge) will continue to the east, north and west of the NHN permit area as it currently does. Irrigation water that now infiltrates into the bedrock zones at NHN will be diverted around the mining area in a HDPE pipeline. Seepage out of the northward advancing high -wall will be diminished from what is currently being experienced from the old Peabody high -wall because the annual recharge from irrigation water flowing across the permit area will be eliminated. In order to develop the impact assessment for groundwater flow and drawdown, two different methodologies were utilized. First, the monitoring data from the old Peabody Nucla Mine were analyzed to determine the annual volume of flow into the pit from actual observations and to also determine the distance of drawdown (cone of depression) observed as the old Peabody Nucla Mine advanced to the north (see Map 2.04.7-1, "Old Peabody Nucla Mine Highwall"). The second method involved the determination of pit inflow rates and drawdown in the adjacent overburden and coal zones as a result of groundwater drainage from the bedrock zones into the pit utilizing a version of the groundwater flow model MODFLOW. A description of the modeling procedures and the assumptions used are provided in Appendix 2.05.6(3)-2. Observation and Analysis Flow from the old mine backfill (SS#l, #2, and #3, see New Horizon 1 Mine Permit) indicate that total seepage from that high -wall varied from a low of about 17 gpm (during periods of no irrigation) to a high of about 52 gpm during irrigation season. The high flow rates average about 42 gpm and the irrigation season is about 165 days Section 2.05.6(3) Page 12 Sept. 2015 (TR -11)