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

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Conclusion DRMS concluded in its Decision and Findings of Compliance Document (1983) for Peabody's New Horizon Mine that no alluvial valley floors exist in either the New Horizon permit area or the potentially affected area (Tuttle Draw) associated with the New Horizon Mine. The tributaries of Tuttle Draw and Coal Creek Canyon are developed on and have incised a dip slope. The water in the drainages runs on top of weathered bedrock strata. The incised channels, with perennial flow, make it infeasible to construct a gravity flow flood irrigation system. WFC therefore concludes that no alluvial valley floors exist along the potentially affected area of Tuttle Draw and Coal Creek Canyon and their tributaries. This conclusion is substantiated by the results of an EPA alluvial valley floor study (EPA 1977) which addresses most coal mining areas of the west and the fact that flood irrigation from drainages is not being practiced. Hydrology Monitoring Plan WFC has developed a baseline hydrological monitoring program for the NHN Permit area with the advice and consent of DRMS. This monitoring program will continue for the foreseeable future and is proposed to be used with possible minor modifications during the mining and reclamation operations. The monitoring program is described in Appendix 2.05.6(3)-3 of this section 2.05.6(3). B) PROBABLE HYDROLOGIC CONSEQUENCES Previous mining by WFC at the New Horizon Mine and Peabody's experience while mining at the old Nucla mine have provided the experience upon which the determinations of "Probable Hydrologic Consequences" are founded. This experience is documented in the New Horizon 1 and New Horizon 2 permit documents and the "Annual Hydrology" reports. The knowledge provided by the long term hydrologic monitoring in relation to the earlier baseline data allows more accurate prediction of consequences than would otherwise occur. Peabody Coal Company performed extensive and detailed computer modeling to determine probable hydrologic 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 1St 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 Section 2.05.6(3) Page 11 Sept. 2015 (TR -11)