GENERAL52614 - Laserfiche WebLink

Home Browse Search

The Middle sandstone lies 61 to 267 feet above the "F" coal (See Figure•4), It is exposed in the valley walls of the Williams Fork and Yampa Rivers in i:he southern part of the permit area and may lie up to 1,700 feet below the surface at the northern end. It has an average thickness of 105 feet over the permit area. No water supply wells are completed in this aquifer either in the permit or adjacent area. Empire Energy has installed six monitoring wells in the Middle sandstone: TR-4; TR-7A; 81-01; 83-01; 83-02; and 83-03. Both ground water levels and water quality data are collected by means of these wells. The applicant's aquifer tests of this sandstone yielded an average permeability value of 0.5 gpd/ft.2 and storativity values ranging from - 0.00033 to 0.0015. The Twentymile sandstone is about 120 feet thick locally and lies approximately 200 feet above the Middle sandstone. The Twentymile Sandstone underlies much of the northern portion of the permit area. It crops out in the Williams Fork Mountains to the south as well as in the valley walls of the Yampa River. Pumping tests performed on the Twentymile sandstone for the Trapper Mine by Utah International Inc. yielded transmissivity values of 77 to 85 gpd/ft. Utah International Inc. felt that these values were low, given yields of 500 gpm from the Twentymile sandstone near the axis of the Big Bottom syncline. A transmissivity value of 5,000 gpd/ft and a permeability value of 50 gpd/ft2 are postulated for the Twentymile sandstone in that area. Empire Energy employs three wells to monitor water levels and quality in the Twentymile sandstone. These are wells 9,259 and 84-01. The White sandstone consists of three separate, massive, cross-bedded sandstone benches (See Figure 4). The individual sandstones are separated from one another by thin series of shales and coals which act as aquicludes and aquitards. Total thickness for the White sandstone is approximately 350 feet. The base of the White sandstone is about 130 feet above the "P" coal seam in which the Eagle No. 9 Mine was located prior to its closing in 1985. The uppermost coal seam mined at Trapper underlies the White sandstone by some 20 to 50 feet. Reportedly, the White sandstone will be in direct hydrologic communication with reclaimed spoils at the Trapper Mine, Three welts 81-03A, 81-04A, and 81-19, were used by Empire Energy Corporation to monitor the White sandstone in the permit area until shortly after closing the Eagle No. 9 Mine. Tests of wells 81-04 and 81-19 yielded permeability values for the aquifer ranging from 0.14 to 0.6 gpd/f t2 and a storativity estimate of 0.0015. Data from the Trapper Mine permit application shows limited ground water also occurs within the lenticular sandstones associated with coal seams and the coal seams themselves in the Mesa Verde Group. The permeabilities of these water hearing zones are normally quite low, generally an order o£ magnitude less than that of the major sandstone aquifers. Most coals are believed to have intrinsically low permeability except where the seams have been fractured by natural stresses or by stresses induced from mining operations. Testing of two wells completed in coal seams roughly equivalent to Empire Energy's "F" seam by Northern Coal Company near Meeker yielded permeabilities averaging 0.07 gpd/ft2. Testing by Northern Coal Company of five wells completed in coals approximately equivalent to the "P" seam provided permeability estimates averaging 8.6 gpd/ft2 and a storativity value of 0.00095. Empire Energy's modeling of the inflows into the No. 5 and -25-