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-14- VIII, probable Hydrologic Consequences of Mining and Cumulative Hydrologic Impact Study - Rules 2.05.6(3) anc 2.07.6(2)(c) This Cumulative Hydrologic Impact Study (CHIS) for the drainage basin of the North Fork of the Gunnison River has been prepared by the Colorado Mined Land Reclamation Division (Ct4LRD) pursuant to Rule 2.07.6 (2)(c). This CHIS assesses the probable cumulative hydrologic impacts of all anticipated coal mining operations upon the general area of the North Fork of the Gunnison River Valley. Included in this assessment are all existing coal rrunes and those proposed coal mines for which permit applications have been submitted to the Division. This study has been prepared using information and analysis contained in the Blue Ribbon Mine permit application, information and analysis contained in other permit applications of 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. ARCO Coal - Mt. Gunnison No. 1 Mine, CPILRD File No. C-007-80 2. Bear Coal Company, Inc. - Bear No. 1, 2, and 3 Mines, CMLRD File No. C-033-8' 3. Colorado Westmoreland - Orchard valley Mine, CMLRD File No. C-038-81 4. U.S. Steel - Somerset Mines, CMLRD File No. C-022-81 5. Western Associated Coal - Blue Ribbon twine, CMLRD File No. C-047-8I 6. western Slope Carbon - Hawk's Nest Mines, CMLRD File No. C-016-8I All of these coal mines have life-of-mine areas within a 247 square mile sub- watershed of the 978 square mile North Fork of the Gunnison drainage basin (Figure 1). 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 I. This assessment is divided into the three major subsections: Description of the Hydrologic Environment, Probable Hydrologic Consequences of the Blue Ribbon Mine and Cumulative Hydrologic Impact Assessment. DESCRIPTION OF THE HYDROLOGIC ENVIRONMENT The first part of this assessment describes the hydrology of the drainage 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; 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 Crand Mesa. The sedimentary strata exposed in the Somerset Coal Field dip at 3 to 5 degrees to the north and northeast.