Laserfiche WebLink
IMPACTS ON GROUND WATER <br />The Mesa Verde formation is a very poor regional aquifer, and consequently, <br />vertical permeability results in greater water flows than horizontal <br />transmissivity. Therefore, discussion of ground water impacts will be <br />focussed on natural and induced fractures. The six underground mines and one <br />loadout along the North Fork of the Gunnison may impact ground water quantity <br />by one or more of the following: <br />o Inflows into the mines through faults and fractures which provide <br />communication between the mine and overlying and underlying aquifers and <br />surface waters. These types of inflow have been experienced at Somerset, <br />Hawk's Nest, Blue Ribbon, Orchard Valley, and Mt. Gunnison No. 1 mines. <br />o Subsidence-induced flows into the mines. Subsidence-caused fracturing <br />could disrupt surface and near surface drainage and storage. However, <br />extensive studies of subsidence fractures in the North Fork by Dunrud <br />(1976) have not shown a direct relationship. The Bureau of Land <br />Management has limited the Orchard Valley Mine to partial extraction <br />beneath colluvial/alluvial deposits in order to minimize any potential <br />subsidence impacts. <br />o Dewatering of the coal, roof and floor with the advance of mining. Minor <br />amounts of water have been noted as discharging in newly-mined areas at <br />the Somerset, Orchard Yalley, Hawk's Nest, Blue Ribbon, and Mt. Gunnison <br />No. 1 mines. The minor amounts indicate that the coal and <br />under-and-overlying strata store and transmit very little water. This <br />also indicates that depletion of ground water sources, as a result of <br />mining, will not occur. <br />DESCRIPTION OF THE SURFACE WATER STUDY AREA <br />The North Fork of the Gunnison River is the major drainage for the general <br />area. 9na11er streams in or adjacent to the life-of {nine areas are all <br />tributary to the North Fork. <br />The North Fork has an average annual streamflow at Somerset of approximately <br />313,500 acre-feet per year (1962-1979). The flow is regulated by the Paonia <br />Reservoir on Muddy Creek five (5) miles upstream of the town of Somerset, <br />which became operational in 1962. River yields during that period have ranged <br />from a high of 601,800 acre-feet per year in water year 1984 to a low of <br />82,270 acre-feet in water year 1977. Waters in the North Fork are a calcium <br />bicarbonate type. There are moderate levels of sulfate. Salinity averages <br />less than 100 mg/1. <br />Just below Paonia Reservoir, Muddy Creek and Anthracite Creek join to form the <br />North Fork of the Gunnison River. Anthracite Creek contributes about <br />two-thirds of the flow to the North Fork. Anthracite Creek is a perennial <br />stream with an average annual yield of 157,313 acre-feet for the period of <br />record between July, 1977 to October, 1980 (U.S.D.I., U.S.G.S., 1980). This <br />corresponds to an average flow rate of 217 cfs. The highest discharge <br />recorded was 4,200 cfs on May 27, 1979. Low flows of 12 cfs have been <br />recorded several times during the period of record. <br />-9- <br />