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-19- those proposed coal mines for which permit applications have been submitted to the Division. This study has been prepared using information and analyses contained in the Orchard Valley Mine permit application, information and analyses contained in other permit applications for mines located in the general area and other available information including site visitation by members of the Division staff. Coal mining operations in the study area include: 1. West Elk Coal Company (WECC) - Mt. Gunnison No. 1 Mine, CMLRD File No. C-007-80 2. Bear Coal Company, Inc. - Bear No. 1, 2, and 3 Mines, CMLRD File No. C-033-81 3. Colorado Westmoreland Inc. (CWI) - Orchard Valley Mine, CMLRD File No. C-038-81 4. U.S. Steel - Somerset Mines, CMLRD File No. C-022-81 5. Blue Ribbon Coal Company - Blue Ribbon Mine, CMLRD File No. C-047-81 6. Western Slope Carbon - Hawk's Nest Mines, CMLRD File No. C-016-81 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 River drainage basin (Figure 1), and have been considered as the mines in the general area for this study. All mining operations in the general area are underground operations. The life-of-mine areas of these 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 5-year permit period and the area to be undermined during the life-of-mine are tabulated in Table 1. This assessment is divided into the three major subsections: Description of the Hydrologic Environment, Probable Hydrologic Consequences of the Orchard Valley Mine, and Cumulative Hydrologic Impact Assessment. DESCRIPTION OF THE HYDROLOGIC ENVIRONMENT The first part of this assessment describes the hydrology of the drainagA basin of the North Fork of the Gunnison River and the mining activity occurring in the basin. This includes: 1) a description of the regional geology; 2) a description of the ground water regime; 3) a description of the surface water regime; and 4) a discussion of precipitation and runoff in the basin. Regional Geology The Somerset Coal Field lies on the southeast margin of the Piceance Basin, and just south of Grand Mesa. The sedimentary strata exposed in the Somerset Coal Field dip at 3 to 5 degrees to the north and northeast.