Laserfiche WebLink
_17_ <br />1) The Coal Basin Mine workings will be over [,UUU feet deep in <br />this area and subsidence effects will not impact surface and <br />yround waters tributary to the North Fork; <br />2) A substantial distance separates the Coal Basin f4ines from the <br />mines in the Somerset Coal Field; <br />3) Geological characteristics of the rock strata differ <br />considerably between the two coal fields; and <br />4) The Coal Basin Mines will not have any surface facilities <br />(disturoances) in the North Fork drainage. <br />All mining operations in the general area are underyround operations. <br />The life-of-mine areas of these mines are illustrated on Fiyure 2. In <br />addition, the coal seams to be mined, the area of surface disturbance, <br />the area to be undermined during the first 5-year permit period and the <br />area to be undermined during the life-of-mine are taoulated in Taole 1. <br />This asses sinent is divided into the three major subsections: Description <br />of the Hydrologic Environment, Probable Hydrologic Consequences of the <br />Somerset P1ine and Cumulative Hydroloyic Impact Assessment. <br />UtSCR1PTIUN OF THE HYDROLOGIC ENVIRONMENT <br />The first part of this assessment descrioes the hydrology of the drainage <br />basin of the North Fork of the Gunnison River and the mining activity <br />occurring in the oasin. This includes 1) a description of the regional <br />geology; t) a description of the ground water regime; 3) a description of <br />tyre surface water reyi~ne; and 4) a discussion of precipitation and runoff <br />in the basin. <br />Regional Geology <br />The Somerset Cu al Field lies on the southeast ~nargiri of the Piceance <br />Basin, and just south of Grand Mesa. The sedimentary strata exposed in <br />the Somerset Coal Field dip at 3 to 5 degrees to the north - northeast. <br />Only minor faulting of limited vertical displacement has been observed in <br />the existing Blue Ribbon, Bear and Hawk's Nest Mines. However, in tt~e <br />Orchard Valley Mine, a fault with a displacement of 50 feet was <br />encountered during mining and drill hole data indicates the presence of <br />other faults in the life-of-mine area with similar displacements. One <br />major fault has been encountered in the Somerset t4ine. The faults which <br />have been encountered in existing mines tend to be high angle normal <br />faults. <br />The steep slopes of the strea;n valleys and the instability of the rock <br />strata in the North Fork Drainage Basin has contributed to numerous <br />landslides, loud flows and ruck falls. These in ass wasting features leave <br />been mapped by W.R. Junge of the Colorado Geological Survey and published <br />as an open file report, entitled "Geologic Hazards, North Fork Gunnison <br />River Valley, Delta and Gunnison Counties, Colorado". <br />