1996-01-26_GENERAL DOCUMENTS - C1980007

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K. Probable Hydrologic Consequences Under Rule 2.07.6(2)(c), the Division is required to make an assessment of the probable cumulative impacts of all anticipated coal mining in the general area, on the hydrologic balance and to make a finding (as discussed in Section A of this document) that the operations proposed in the permit application have been designed to prevent material damage to the hydrologic balance outside of the proposed permit area. This section of the findings document is divided into the following subsections: Description of the Hydrologic Environment, Probable Hydrologic Consequences of the West Elk Mine, and Summary and Findings. A separate Cumulative Hydrologic Impact Study (CHIS) is available for review at the Division of Minerals and Geology. The Cumulative Hydrologic Impact Study (CHIS) filed at the DMG office assesses the projected cumulative hydrologic impacts of all anticipated mining operations in the general area of the West Elk Mine on the North Fork of the Gunnison River Valley. 1. Description of the Hydrologic Environment a. Regional Geology For information regarding regional geology, see Section A, Description of the Environment, Geology in this Findings Document. b. Ground Water Six categories of potential aquifers occur in the Somerset Coal Field. These are: 1) the alluvial and terrace deposits associated with the North Fork of the Gunnison River; 2) the localized, shallow alluvium along creeks tributary to the North Fork; 3) the discontinuous, lenticular and laminar sandstones of the Mesaverde Formation; 4) the Rollins Sandstone; 5) the coal seam; 6) shallow colluvial surficial deposits; and 7) fracture zones in bedrock. The most continuous sandstone aquifers of any significance in the region are the Rollins Sandstone and the massive sandstone separating the Upper and Lower Coal members of the Mesaverde Formation. However, the latter massive sandstone produces very little water, as evidenced by the dryness of the Bear Mine and the lack of springs associated with this unit. Also, the Rollins Sandstone has been found to have insufficient yield to sustain ground water supply wells (Orchard Valley Mine MRP). This unit lies 270 feet below the F coal seam which has been mined. In the Jumbo Mountain area, the Rollins Sandstone appears to be hydraulically isolated. To the south and west, the Rollins Sandstone outcrops in the form of cliffs; and to the north and northeast, it discharges into the North Fork of the Gunnison River. In the Jumbo Mountain area, the average interburden thickness between the B Seam and the Rollins Sandstone is 150 feet. 23