2008-03-21_PERMIT FILE - C1980007A (4)

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West Elk Mine prevents active groundwater flow. Monitoring well hydrographs suggest that the vertical movement of active zone groundwater is less than 100 feet below the ground surface; however, it is likely that the active zone may locally extend for 200 to 500 feet below ground surface. hactive groundwater flow regimes contain old groundwater (i.e., thousand of years), have very limited hydraulic communication with the surface and active groundwater flow systems, and are not influenced by either annual recharge events or short tern climatic variability. Inactive groundwater systems occur more than about 200 to 500 vertical feet from the surface and greater than about 500 to 1,000 feet from cliff faces. Groundwater in these systems located above coal bearing horizons tends to occur in sandstone channels. These sandstone channels are vertically and horizontally isolated from each other and when encountered in mine workings are usually drained quickly. Swelling clays and impermeable shales in the rocks in the unsaturated zone between the near- surface active systems and deeper inactive systems effectively prohibit downward vertical migration of waters fiom the active systems. In the study area, the active zone includes alluvial, mantle cover and landslide materials, and near surface exposures of the Barren Member and Upper and Lower Coal Members. The inactive zone includes deeper rocks of the Barren Member, Upper and Lower Coal Members and the Rollins Sandstone. Exhibit 18 contains Mayo and Associates' complete hydrogeologic analyses of the pen-nit and adjacent areas. A 2004 Mayo and Associates report (Exhibit 18B) provides an assessment of • the hydrogeologic conditions associated with the E Seam in the South of Divide permit revision area. Section 2.05.6 of this permit document addresses important findings from the permit revision submittal and decision documents for the Jumbo Mountain (PR-05, 10/21/94), Apache Rocks (PR-06, 1/26/96), Box Canyon (PR-08, 1/25/00), and current MCC permit document, regarding the lack of groundwater at the mine. Further reference should be made to these exhibits and pen-nit section for specific details. In summary, areally extensive groundwater systems and aquifers do not occur in the study area. This is due to: 1) the steep cliff-face exposures of many bedrock formations, and 2) the heterogeneous lithologies of bedrock formations, which prevent significant vertical or horizontal movement of the limited recharge to bedrock groundwater systems. Groundwater encountered in mine workings is associated with the inactive zone and not in hydraulic communication with groundwater in the active zone represented by the near surface colluvium and alluvium. These mine inflows are localized and do not form areally extensive systems having hydrodynamic communication with each other. Therefore, neither the coal seams nor the overburden units within the permit area transmit groundwater in sufficient quantity to sustain water supplies. 2.04-57 Revised June 2005 PRIO, March 2006; Rev. Apri12006 PRIO, Sep. 2007PR12