GENERAL39876 - Laserfiche WebLink

Home Browse Search

-16- presented in Exhibits 2.7.2.D. - 2.7.2.F. The structure on top of the F-seam is presented on Exhibit 2.7.5.A and geologic maps are presented in Exhibits 2.7.1.A.A and 2.7.2.D.1. Coal is to be produced from the Mesa Verde Formation, a 2,500-foot-thick sequence of beds overlain by the Ohio Creek Conglomerate and underlain by the Mancos Shale. The Mesa Verde Formation is composed of four members, the Rollins Sandstone, the Upper and Lower Coal members, and the "Barren" Member. See generalized stratigraphic column, Figure 2.7.2.A, and description on pages 2-219 through 2-227d of the permit application. The lowermost member of the Mesa Verde Formation, the Rollins Sandstone, is a white to buff-colored, well-sorted, medium-grained sandstone, ranging from 150 feet to 300 feet thick in the permit area. The Lower Coal Member overlies the Rollins Sandstone and consists of interbedded sandstones, siltstones, coals, and shale. The unit averages 270 feet thick in the permit area and bears three significant coal seams--the A, B, and C seams. A massive sandstone, 25 feet in thickness which lies at the top of the Lower Coal Member and separates it from the Upper Coal Member. The Upper Coal Member is approximately 220 feet thick, containing shales, siltstones, sandstones, and the D, E, and F coal seams. The Mt. Gunnison No. 1 Mine will be located in the upper most seam, the F seam. At the mine site, the coal is immediately overlain and underlain by shale. Overlying the Upper Coal Member is the Barren Member of the Mesa Verda Group. This unit consists of interbedded sandstones, siltstones, shales, and coals. The unit is not thought to be of marine origin and, as a result, the sandstones and the coals are highly lenticular, discontinuous, and of limited lateral extent in outcrop. This unit ranges up to 1,500 feet thick and outcrops throughout most of the 5-year permit area. Ground water occurs in both the sandstones and the coal seams of the Mesa Verda Formation. Regional ground water movement is northeasterly, down the dip of continuous stratigraphic units. Local ground water movement is controlled by topography, faults, fractures, and discontinuous lenticular sandstones. 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 Mesa Verda 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. Coal seams within the Mesa Verda Formation also act as continuous aquifers. The Barren Member of the Mesa Verda Formation contains lenticular channel sandstones, some of which may have sufficent length and thickness to transmit ground water flows regionally. Regional ground water aquifers will be recharged along