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West Elk Mine <br />. Inactive groundwater flow regimes contain old groundwater (i.e., thousand of years), have very <br />limited hydraulic communication with the surface and active groundwater flow systems, and aze not <br />influenced by either annual rechazge events or short term climatic variability. Inactive groundwater <br />systems occur more than about 200 to 500 vertical feet from the surface and greater than about 500 <br />to 1,000 feet from cliff faces. Groundwater in these systems located above coal bearing horizons <br />tends to occur in sandstone channels. These sandstone channels aze vertically and horizontally <br />isolated from each other and when encountered in mine workings are usually drained quickly. <br />Swelling clays and impermeable shales in the rocks in the unsaturated zone between the neaz- <br />surface active systems and deeper inactive systems effectively prohibit downward vertical migration <br />of waters from the active systems. <br />In the study azea, the active zone includes alluvial, mantle cover and landslide materials, and neaz <br />surface exposures of the Barren Member and Upper and Lower Coal Members. The inacfive zone <br />includes deeper rocks of the Barren Member, Upper and Lower Coal Members and the Rollins <br />Sandstone. <br />Exhibit 18 contains Mayo and Associates' complete hydrogeologic analyses of the permit and <br />adjacent azeas. A 2004 Mayo and Associates report (Exhibit 18B) provides an assessment of <br />the hydrogeologic conditions associated with the E Seam in the South of Divide permit <br />revision area. Section 2.05.6 of this permit document addresses important fmdings from the <br />permit revision submittal and decision documents for the Jumbo Mountain (PR-05,10/21/94), <br />Apache Rocks (PR-06, 1/26/96), Box Canyon (PR-08, 1/25/00), and current MCC permit <br />document, regarding the lack of groundwater at the mine. Further reference should be made to <br />these exhibits and permit section for specific details. <br />In summary, azeally extensive groundwater systems and aquifers do not occur in the study azea. <br />This is due to: 1) the steep cliff-face exposures of many bedrock formations, and 2) the <br />heterogeneous lithologies of bedrock formations, which prevent significant vertical or horizontal <br />movement of the limited rechazge to bedrock groundwater systems. Groundwater encountered in <br />mine workings is associated with the inactive zone and not in hydraulic communication with <br />groundwater in the active zone represented by the near surface colluvium and alluvium. <br />These mine inflows are localized and do not form areally extensive systems having <br />hydrodynamic communication with each other. Therefore, neither the coal seams nor the <br />overburden units within the permit azea transmit groundwater in sufficient quantity to sustain <br />water supplies. <br />Site Hydropeolopy <br />The most significant hydrogeologic units present within the West Elk Mine property include (from <br />bottom to top) the Mancos Shale, Mesaverde Formation (including the Rollins Sandstone, Lower <br />Coal Member, Upper Coal Member, and the Barren Member), and the colluvium and alluvium <br />along the drainage side-slopes and valley bottoms, respectively (Map 9). Amore detailed <br />discussion of the stratigraphic units within the permit area can be found in Section 2.04.6, Geology <br />Description. The general significance of these stratigraphic units from a hydrogeological <br />perspective is discussed below. <br />2.04 -57 Revised November 2004 PRIO <br />