GENERAL42468 - Laserfiche WebLink

Home Browse Search

_17_ All of these coal mines have life-of-mine areas within a 247 square mile subwatershed of the 978 square mile North Fork of the Gunnison drainage basin. All mining operations in the general area are underground operations, with the exception of Terror Creek Loadout which is strictly a loading facility. The,life-of-mine areas of the underground mines are plotted on Figure 2. In addition, the coal seams to be mined, the area of surface disturbance, the area to be undermined during the first five year permit period and the area to be undermined during the life-of-mine are tabulated in Table 1. s This assessment is Description of the Consequences of the Impact Assessment. GENERAL BACKGROUND divided into the three major subsections: General Hydrologic Environment, Probable Hydrologic Mt. Gunnison No.l Mine and Cumulative Hydrologic The Mt. Gunnison No. 1 Mine lies on the southeast margin of the Piceance Basin. Sediments ranging from late Cretaceous to early Tertiary age, and dipping 3-5 degrees north to northeasterly, are exposed in the mine areas. Structural-Strat.igraphic cross sections are 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, 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.