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West Elk Mine <br />Effects of Subsidence <br />The effects of subsidence from mining of the B Seam in the Apache Rocks and Box Canyon <br />mining azeas and the E Seam in the SOD permit revision area are discussed in Section 2.05.6 <br />(6)(e)(i). Water quality impacts from subsidence could potentially result from: (1) increased <br />stream erosion rates due to alteration of channel slopes and geometry; or (2) cross-connection of <br />previously isolated formations and the surface hydrologic system. <br />The amount of subsidence predicted to result from the Apache Rocks, Box Canyon, and South <br />of Divide mining areas are discussed in Section 2.05.6 (6)(b)(i). As discussed previously in <br />this section, the amount and pattern of change in the channel slope due to subsidence is not of a <br />magnitude to cause significant channel degradation and erosion (see Exhibit 55 and SSA). Small <br />adjustments could occur which would stabilize in a relatively short period of time. <br />From the standpoint of groundwater quality effects resulting from subsidence, the key <br />consideration is that groundwater resources which could be disrupted by the proposed mining aze <br />very limited in extent and magnitude. There is no demonstrated formation groundwater use at <br />the mine or in the general area. There are no formations in the existing or proposed permit azea <br />that would qualify as "aquifers." As discussed in the Groundwater Quality Effects section, if <br />groundwater moves via asubsidence-caused fracture from a higher formation to a lower <br />formation or into the B or E Seams, the water quality change will not be significant. <br />Groundwater OuantitV Effects <br />This section of the application defines and evaluates the hydrologic consequences related to <br />groundwater quantity including impacts from construction of mine entries, the direct mining <br />impacts resulting from single-seam mining (F, B and E Seams) in the original permit area, multi- <br />seam mining (B and E Seam), and the storage of water in previously mined down-dip sealed <br />panels (lazge capacity sealed sumps). Groundwater quality effects aze discussed in the following <br />section. Readers aze encouraged to review Sections 2.05.6 (3)(a-c), West Elk Mine Experience <br />and Regional Mining Experience, of this permit document, because they contain important <br />findings regarding groundwater from the Box Canyon Decision Document the West Elk Mine <br />permit document, including revisions and renewals, other mines in the North Fork Valley, and <br />the CHIA. <br />Surface and groundwater occurrence have been studied extensively by MCC since 1976. Map <br />34 shows the existing hydrologic monitoring network. The groundwater network for the permit <br />azeas consists of groundwater monitoring wells which aze used to monitor and collect water level <br />and water quality data. <br />The nature of the groundwater resources at the mine is described in Section 2.04.7 and is not <br />repeated herein. However, from the standpoint of determining probable hydrologic <br />consequences, it is necessary to distinguish among the different groundwater regimes found at <br />the site. These include the active and inactive groundwater zones. The active groundwater <br />zone includes the near surface waters derived from rain and snowmelt stored in the near <br />surface alluvium, colluvium and near surface bedrock formations (generally less than 500 <br />• feet in depth). The inactive zone exists in the bedrock formations and contains ancient <br />2.05-144 Revised June 1005 PRIG; Rev. March 1006, Rev. May 1006 PRIG <br />