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West Elk Mine <br />2.04.7 Hydrology Description <br />The purpose of this section is to provide a broad overview of surface water and groundwater <br />hydrology for the permit area. Important subjects relative to hydrology are also addressed in other <br />sections including: Geology (2.04.6), Climatology (2.04.8), Soils (2.04.9), and Vegetation (2.04.10). <br />The reader is urged to review these sections. For information pertaining to alternate water supply, <br />refer to Section 2.05.6. <br />To complete specialized research and evaluation, and devote particular attention to hydrologic and <br />subsidence phenomena resulting from mining, including the probable hydrologic consequences of <br />mining for PR-10 and 11, MCC retained Wright Water Engineers, Inc. (WWE) of Denver, and <br />Glenwood Springs, Colorado. WWE has 40 years of experience on diverse water resource <br />assignments. MCC also retained HydroGeo, Inc. (HydroGeo) of Crested Butte, Colorado to review <br />the hydrology sections of the PR-12 application and complete Exhibit 71, Hydrologic <br />Characterization of the South of the Divide area and Monitoring Plan, West Elk Mine (WEM). <br />HydroGeo has completed the hydrologic monitoring and Annual Hydrology Reports for the WEM <br />since 2001. For this PR-12 assignment, MCC utilized the following experts or advisors: <br />Mr. Tom Grey, P.E., subsidence and hydrologic impacts from subsidence <br />Mr. Michael Egan, P.G., geology, hydrogeology, and natural hazards <br />Mr. Chris Hayes, Geologist, sediment transport and fluvial morphology <br />Mr. Joe Frank, M.S., Exhibit 71, South of Divide Hydrology Monitoring Plan <br />0 2.04.7(1) Groundwater Information <br />West Elk Mine has historically been considered a dry mime. Previous studies by MCC and its <br />consultants have shown that groundwater inflows encountered within the mine workings were <br />associated with perched conditions within the Upper and Lower Coal Members of the Mesaverde <br />Formation. These studies concluded that there was no stratigraphic unit above the Rollins <br />Sandstone that had the stratigraphic continuity or water-yielding capacity to be considered a <br />potential regional aquifer (see Figures 5A, 5B, 5C, 5D, 5E, and 5F in map pockets). See Section <br />2.04.6 (Geology Description) for a detailed discussion of the geologic units associated with, and in <br />close proximity to, the West Elk Mine workings. See also Exhibits 17A, 18, and 18B for additional <br />discussions relative to groundwater conditions and relationships. <br />Within West Elk Mine, groundwater inflows have manifest themselves as roof inflows from sandstone <br />channels located in the lower portion of the Mesaverde Formation, floor inflows associated with the <br />underlying sandstone unit, rib/roof inflows associated with fractures storing finite volumes of <br />groundwater, and, as manifest in early 1996, damage zones associated with fault systems. Conceptual <br />groundwater flow is shown on Figure 7F and the potentiometric surface of the groundwater in the E Seam <br />is presented on Map 1 of Exhibit 71. <br />In early March 1996, B Seam development mining of the B East Mains near the Northeast Panels <br />intersected a SE-NE trending fault system (B East Mains (BEM) Fault) which initially produced <br />about 500 gpm. This same fault was subsequently crossed by mining several times with <br />• observed groundwater inflows reaching as much as 2,500 gpm. Each progressive mining <br />intersect of the BEM Fault was generally down-dip from the previous one resulting in a <br />2.04-51 Revised June 2005 PR10, March 2006; Rev. April 2006 PR70, Sep. 2007PR12