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-26- Two levels of alluvial terraces were identified adjacent to the Purgatoire River. These terraces are located 5 to 10 feet and 40 to 50 feet above the river in the study area and have been investigated by Powell, 1952. They are composed of relatively unweathered, gray to light tan alluvium overlain by medium to dark brown sandy overbank deposits. These terraces support typical hydrophytic vegetation characteristic of floodplains and contain ground water hydrologically connected to the river. Absolute dates on the alluvial deposits are not available; however, in analogous areas of the Rocky Mountain Region, the strath terraces are of Pleistocene age and the alluvial terraces of Holocene age. B. Ground Water - Bedrock Aquifers The Trinidad Sandstone is a significant regional aquifer given its 250 feet thickness and regional extent. This sandstone is the first major aquifer below the lowest coal seam to be mined and is separated from the coal seam by up to 900 feet of interbedded and lenticular shales, siltstones, and sandstones. The Trinidad Sandstone will not be impacted by mining in the A1]en and Maxwell Mines. The coal seams and most of the overburden in the permit area are part of the Raton Formation. Sandstones in the formation are interbedded and lenticular. These characteristics of the formation inhibit the vertical and horizontal flow of ground water through it. ~,/ Little or no ground water has been encountered during the exploration phases ~i at the Allen and Maxw ine Small amounts of water are encountered in the ,C. coal seams during mining. Minor amounts of water were encountered within „r~+ minor coal beds that were intersected during mine development. Small amounts U"I of ground water may be found in the sandstone units and fractures occurring in the formation. The applicant has conducted ]aboratory permeability and porosity tests on twenty-three samples of selected sandstone intervals collected from cores. Because of the lack of correlation, core samples were selected from those intervals that appeared to be the most permeable. Measured values of the vertical intrinsic permeabilities of the sandstones of the Raton Formation fell within a narrow range of 0.12 - 1.65 millidartiies. Horizontal intrinsic permeabilities were determined for 5 samples. Their values ranged from 0.08 to 2.4 millidarties. The test results indicate that the channel sandstones in the Raton Formation in the vicinity of the Allen and Maxwell mines are quite uniform with respect to permeability, even though these sandstones are / vertically and horizontally discontinuous. The applicant has also provided the results of three pump tests conducted at the Maxwell Mine. In two wells (LA 221A and LA 218A) the open-interval available for water entry included the Maxwell seam, and various thicknesses of shale, siltstone, and sandstone immediately above and below the coal seam. No significant water was encountered in either hole until the Maxwell Coal Seam was penetrated. Therefore, the permeability values determined are for the coal. The tests found permeabilities of 0.02 and 0.04 ft/day, transmissivities of 0.56 and 1.98 ft2/d, and storage coefficients of 1 x 10-5 and 8 x 10'5. The permeability and transmissivity values are low and the storage coefficients are indicative of confined aquifers.