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

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consequences of mining for the New Horizon Mine. Details of the computer modeling are available in Attachment 2.05.6(3)-2 of New Horizon 2 Mine permit. While some of the old Peabody Nucla Mine monitoring was suspended in 1987, some of the monitoring holes and surface water monitoring sites have been revisited (monitoring resumed in 1 st quarter of 2007) as part of the "2 year close out" for the New Horizon 1 permit area. Three "old" ground water monitoring holes of particular interest that have been monitored during 2008 and 2009 include GW -N3, GW -N8, and GW -N9. As indicated on Figure 2.05.6(3)-1, hydraulic flow south of Meehan Draw at the New Horizon North Mine will generally travel from north to south through the boxcut area and into the old backfill south of the Old Peabody Nucla Mine Highwall. During excavation of the initial boxcut, a buffer of unmined coal and overburden was left in place at the location of the old Peabody Highwall (see Map 2.05.4-2). The purpose of this "buckwall" is to maintain a buffer between the mine spoils from previous surface mining activities and the current active mining pit to provide a 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 Section 2.05.6(3) Page 11 April 2016 (PR -01)