GENERAL37970 - Laserfiche WebLink

Home Browse Search

-39- CU~'(ULATIVE HYDROLOGIC IMPACT ASSESSMENT It~acts on Ground Water The six underground mines along the North Fork of the Gunnison may impact ground water quantity by one or more of the following: - induced inflows into the mines through faults and fractures which provide communication between the mine and overlying and underlying aquifers and surface waters; - dewaterinq of the coal, roof and floor with the advance of mining; and - subsidence-induced flows into the mines. Faults and Fractures Faults and fractures which cut the bedrock strata produce a localized increase in porosity within the strata. If the faults and fractures do not become sealed by clays, they may become conduits for the flow of ground and surface water. When encountered within the mine, faults and fractures will dewater. The amount of water flowing into the mine from these sources depends on porosity and permeability of faults or fractures, and on the open vertical connection within the faults and fractures between the coal seam and sources of ground or surface water. Fault and fracture controlled inflows have been noted and mapped in the U.S. Steel Corporation Somerset Mine application (Exhibit E8-3366), the Western Slope Carbon Har/k's Nest Mine permit application (Exhibit 2.04.7(1) or W-1006), and the AZ ue Ribbon Coal Co., Blue Ribbon Afine application (Exhibit T). Colorado Westmoreland, Inc. has not mapped inflows to date. However, then have noted in floras in faulted areas. No inflow mapping is available at present for the Bear mines. However, the company states that it is not presently experiencing any mine inflows. The Mt. Gunnison No. I l9ine has encountered only minor inflows from fractures in the number 1 portal. Dewatering of Coal, Roof, and Floor From field observations made by CMLRD hydrologists in the mines and from information contained in their respective permit applications, water was noted to seep from the coal, roof, and floor upon advance of mining in the "B" and "C" seams of the Somerset Mine, the "D" seam of the Orchard Valley Mine, the "E" seam of the Hawk's Nest Mine and Blue Ribbon Mine, and "F" seam of the Mt. Gunnison Mine. These sources of mine inflows dry up one to two weeks after mining an area. The minor amount of water resulting from derratering of the coal, roof, and floor indicates that the coals and the overlying and underlying strata in the Aesaverde Formation have very low permeabilities. Thus, these strata store and transmit very Iittle water and are not considered aquifers. Therefore, the impacts of dewaterinq the coals and the strata immediately above and below the coals within the Mesaverde Formation will have an insignificant impact on the hydrologic balance. Also, the very slow rates of inflora resulting from dewaterinq strata indicated that these strata will not transmit significant quantities of water which will result in depletion of surface water sources.