Laserfiche WebLink
<br />-18- <br />B. Ground Water - Bedrock Aquifers <br /> <br />The Trinidad Sandstone is a significant regional aquifer given its 250 feet <br />thickness and regional extent. This sandstone is the first major aquifer <br />below the lowest coal seam to be mined and is separated from the coal seam by <br />up to 900 feet of interbedded and lenticular shales, siltstones, and <br />sandstones. The Trinidad Sandstone will not be impacted by mining in the New <br />Elk and Golden Eagle Mines. <br />The coal seams and most of the overburden in the permit area are part of the <br />Raton Formation. Sandstones in the formation are interbedded and lenticular. <br />These characteristics of the formation inhibit the vertical and horizontal <br />flow of ground water through it. <br />Little or no ground water has been encountered during the exploration phases <br />at the New Elk and Golden Eagle mines. Small amounts of water are encountered <br />in the coal seams during mining. Minor amounts of water were encountered <br />within minor coal beds that were intersected during mine development. Small <br />amounts of ground water may be found in the sandstone units and fractures <br />occurring in the formation. <br />The applicant has conducted laboratory permeability and porosity tests on <br />twenty-three samples of selected sandstone intervals collected from cores. <br />Because of the lack of correlation, core samples were selected from those <br />intervals that appeared to be the most permeable. Measured values of the <br />vertical intrinsic permeabilities of the sandstones of the Raton Formation <br />fell within a narrow range of 0.12 - 1.65 millidarcies. Horizontal intrinsic <br />permeabilities were determined far 5 samples. Their values ranged from 0.08 <br />to 2.4 millidarcies. The test results indicate that the channel sandstones in <br />the Raton Formation in the vicinity of the New Elk and Golden Eagle mines are <br />quite uniform with respect to permeability, even though these sandstones are <br />vertically and horizontally discontinuous. <br />The applicant has also provided the results of three pump tests conducted at <br />the Golden Eagle Mine. In two wells (LA 221A and LA 218A) the open-interval <br />available for water entry included the Maxwell seam, and various thicknesses <br />of shale, siltstone, and sandstone immediately above and below the coal seam. <br />No significant water was encountered in either hole until the Maxwell Coal <br />Seam was penetrated. Therefore, the permeability values determined are for <br />the coal. The tests found permeabilities of 0.02 and 0.04 ft/day, <br />transmissivities of 0.56 and 1.98 ft2/d, and storage coefficients of 1 x <br />10-5 and 8 x 10-5. The permeability and transmissivity values are low and <br />the storage coefficients are indicative of confined aquifers. <br />The third well (LA 264) was designed to provide an assessment of the water <br />bearing capacity of the overburden in addition to that provided by the core <br />permeability tests. The open interval in this well began at a depth of 62 ft. <br />and ended at a depth of 276 ft. During drilling, water inflow was encountered <br />at about 72 ft. The inflow was estimated to be about 15 gpm and no <br />significant increase in discharge was observed over the remainder of the <br />hole. It is probable that a thin fracture zone at the 72 ft. level accounts <br />for most all of the water produced by this well. This well had a permeability <br />of 0.42 ft/d and a transmissivity of 90.1 ft2/d. <br />