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West Elk Mine <br />2.04 -57 Rev. 06/05- PR10, 03/06- PR10, 04/06- PR10, 09/07- PR12; 05/22- MR462 <br /> <br /> <br />by short-term climatic variability. Groundwater in these systems circulates shallowly and has short <br />flow paths. The active regime includes alluvial groundwater and near-surface exposures of all <br />bedrock formations except, perhaps, the Mancos Shale. The “near surface” extends about 500 to <br />1,000 feet into cliff faces or exposed ridgelines where flow is controlled by fractures and channel <br />sands. Further into the cliff faces and ridgelines the discontinuous character of channel sands <br />prevents active groundwater flow. Monitoring well hydrographs suggest that the vertical movement <br />of active zone groundwater is less than 100 feet below the ground surface; however, it is likely that <br />the active zone may locally extend for 200 to 500 feet below ground surface. <br /> <br />Inactive groundwater flow regimes contain old groundwater (i.e., thousands of years), have very <br />limited hydraulic communication with the surface and active groundwater flow systems, and are not <br />influenced by either annual recharge 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 are 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 near- <br />surface active systems and deeper inactive systems effectively prohibit downward vertical migration <br />of waters from the active systems. <br /> <br />In the study area, the active zone includes alluvial, mantle cover and landslide materials, and near <br />surface exposures of the Barren Member and Upper and Lower Coal Members. The inactive zone <br />includes deeper rocks of the Barren Member, Upper and Lower Coal Members and the Rollins <br />Sandstone. <br /> <br />Exhibit 18 contains Mayo and Associates’ complete hydrogeologic analyses of the permit and <br />adjacent areas. A 2004 Mayo and Associates report (Exhibit 18B) provided an assessment of the <br />hydrogeologic conditions associated with the E Seam in the South of Divide permit area. Section <br />2.05.6 of this permit document addresses important findings from permit revision submittals and <br />decision documents regarding the general lack of groundwater at the mine. Reference these exhibits <br />and permit sections for specific details. <br /> <br />In summary, areally extensive groundwater systems and aquifers do not occur in the study area. <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 recharge 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. These <br />mine inflows are localized and do not form areally extensive systems having hydrodynamic <br />communication with each other. Therefore, neither the coal seams nor the overburden units <br />within the permit area transmit groundwater in sufficient quantity to sustain water supplies.