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Probable Hydrologic Consequences New Elk Mine 11 <br />3.2.2 Raton Aquifer <br />Based on completion reports from 126 CBM wells in Las Animas County, Watts (2006a) estimates that the <br />thickness of the Raton Formation ranges from about 1,100 to 1,900 ft where it is not eroded. Net coal <br />thickness is about 100 ft, and the Raton Formation may contain as many as 40 coal beds that are lenticular, <br />1 to 10 ft thick, and have limited lateral continuity of about 500 to 1,000 ft. (Clarke and Turner, 2002). <br />The following description of the Raton Aquifer is from Watts, 2006a. <br />The Raton Formation includes upper, middle, and lower members (Wood and others, 1951). The three <br />members of the Raton Formation are not distinguishable, except by stratigraphic position, and recognition of <br />them was based primarily on the lateral persistence of sandstone zones at outcrop. The lower member differs <br />from the middle and upper members, because it contains a basal conglomerate, which thins eastward and <br />becomes finer grained (Wood and others, 1956). Generally, the lower contact of the Raton Formation with the <br />Vermejo Formation, as indicated by the basal conglomerate, is erosional, but locally, the contact may be <br />conformable. Coal, conglomerate, and sandstone in the Raton Formation are capable of transmitting substantial <br />quantities of water to wells. Because of the interbedded and lenticular nature of its strata, the Raton aquifer is a <br />highly heterogeneous and anisotropic aquifer. <br />Water levels in the Raton Formation are highly variable depending on a number of factors including <br />location, well completion depth, lithology, and pumping activities related to CBM production. <br />Groundwater may be confined or unconfined depending on stratigraphic conditions and location. The <br />formation is highly heterogeneous and groundwater elevations can vary significantly over short lateral and <br />vertical distances. Well records from CDWR indicate that there are 19 permitted wells in the Raton <br />Formation within a one mile radius of the permit boundary (Table 6 and Plate 3). The wells vary in depth <br />from 30 to 750 feet, and have completion water levels ranging from 5 to 598 feet bgs. Well yields from the <br />Raton Formation near the mine range from 0.5 to 112 gpm, with most wells reporting yields of 5 to 15 <br />gpm. <br />Pumping for CBM production impacts water levels in Raton Formation coal seams. Currently 129 CBM <br />wells are located within a one -mile radius of the permit boundary (Plate 4). The well field operator, XTO, <br />indicates that it is standard practice to perforate production wells across all coal seams with thicknesses <br />greater than one foot. Watts (2006b) evaluated the potential for CBM production in Las Animas county to <br />impact water levels in wells that are used for water supply. He noted that "[b]ecause the permeability of <br />stratified sedimentary rocks generally is greaterparallel to bedding than across bedding, it is assumed that <br />CBM production likely would have the greatest potential for interfering with nearby water - supply wells, in <br />areas in which there is no or little vertical separation between their respective production intervals ". The <br />analysis assumed that a vertical separation of 100 feet between CBM and water supply wells would be <br />protective of water supplies, but it was careful to note that the required separation would depend on local <br />geologic conditions. <br />The Raton Formation generally has low permeability and most groundwater flow occurs in fractures, joints, <br />and along bedding planes. Sandstone, siltstone, and mudstone beds have low primary permeability and <br />contain clay in the matrix or are cemented by silica or calcite. Coal seams generally have higher <br />permeability than the clastic rocks, and groundwater flow is transmitted through secondary features (i.e. <br />cleats). The Colorado Geological Survey (CGS) estimates that transmissivities in the Raton - Vermejo <br />Aquifer range from about 0.02 to 79 W /day. Single well pumping tests in the Maxwell seam at the Golden <br />Eagle Mine returned hydraulic conductivity values ranging from 0.06 to 0.22 ft/day (WWL, 1980). Coal <br />transmissivities from the same pumping tests returned values ranging from 0.56 to 127 W /day. One test in <br />a two -foot thick fractured sandstone interval returned a hydraulic conductivity value of 45.4 ft /day. The <br />tramsmissivity of the interval is calculated to be 91 W /day. The average porosity of Raton Formation <br />sandstones based on 21 laboratory tests of core from the Maxwell Mine is 9.6 percent (WWL, 1980). <br />WWL estimated Raton Formation storativity to be about 0.005. <br />4164A.110421 Whetstone Associates <br />TA GA Q(Al D­ 1 21 A IM 1 1 <br />