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-zz- 5. Western Associated Coal - Blue Ribbon Mine, CMLRD File No. C-047-81 b. Western Slope Carbon - Hawk's Nest Mines, CMLRD File No. L'-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 drainage basin (Figure 1), and have been considered as the mines in the general area for this study. The Mid Continent Resources, Coal Basin Mines will extend into the upper tributaries of Muddy Creek, a tributary to the North Fork of the Gunnison (figure 1). These mines were excluded from this CHIS for the following reasons: 1) The Coal Basin Mine workings will be over 2,000 feet deep in this area and subsidence effects will not impact surface and ground waters tributary to the North fork; 2) A substantial distance separates the Coal Basin 19ines from the mines in the Somerset Coal Field; 3) Geological characteristics of the rock strata differ considerably between the two coal fields; and 4) The Coal Basin Mines will not have any surface facilities (disturbances) in the North Fork drainage. All mining operations in the yeneral area are underyround 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 duriny the life-of-mine are tabulated in Table 1. This assessment is divided into the three major subsections: Description of the Hyorologic Environment, Probable Hydrologic Consequences of the Hawk's Nest Mine and Cumulative Hydrologic Impact Assessment. DESCRIPTION OF THE HYDROLOGIC EIVVIRONMENT The first part of this assessment describes the hydrology of the drainage oasin 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. kegional Geology The Somerset Coal Field lies on the southeast margin of the Piceance Basin, antl 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.