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<br />• <br />• <br />~~ <br />(1 <br />Doc Date:1211112001 III III IIIIIIIIII III <br />1J <br />2.04.7.0 Introduction <br />The surface and groundwater hydrology discussions presented in the following <br />sections are based on existing published information, maps and limited field <br />investigations. All field work was performed by Panorama Resources. Applied <br />Hydrology Associates, Inc. was responsible for analysis and interpretation of <br />the field data provided by Panorama Resource Services, Inc. <br />2.04.7.1 GROUND WATER HYDROIAGY <br />The Rimrock Strip Mine Site is located in the Raton ground water basin near <br />Trinidad, Colorado. The regional ground water flow direction is north- <br />northwest. Within a half mile radius of the mine site there are six wells <br />that are used for domestic purposes, livestock, pasture and lawn watering <br />and/or monitoring. These wells have been completed at depths ranging from <br />26.5 to 200 feet in both the Trinidad sandstone and the Vermejo formation. On <br />April 11-15, 1988 and again on May 20, 1988 the water levels in the wells and <br />field ground water quality parameters were determined (see Table 3). During <br />April of 1988 three area walls and the mine discharge (also ground water) were <br />sampled and analyzed for a full suite of chemical parameters (see Appendix 4). <br />The depths to water ranged from 9.1 feet below land surface at the Windmill <br />Well which is completed in the Vermejo formation to 81.4 feet below land <br />surface in Well 29-4 which is completed in both the Vermejo and the Trinidad <br />sandstone (see Table 2). Twelve (12) boreholes were drilled on the mine site <br />and adjacent area in order to assess the formation depths and thicknesses. <br />2.04.7.1.1 Aquifer Characteristics <br />The lowermost principal aquifer in the Raton basin 'is the Trinidad Sandstone <br />which is exposed immediately to the north of the site. It overlies the <br />impermeable Pierre Shale. The Trinidad Sandstone consisting primarily of <br />tightly-cemented sandstones. It has been reported to yield in the range from <br />0.5 to 5.0 gpm from wells in the Raton Basin. Overlying the Trinidad <br />Sandstone is the Vermejo formation which outcrops at the surface at the site <br />although it is sometimes concealed by the Raton formation. The Vermejo <br />formation consists mainly of sandstone and coal lenses interbedded with shale. <br />It has a reported yield of 0.5 to 20 gpm. Overlying the Vermejo formation is <br />the Raton formation. <br />The regional hydrologic study performed by the U.S. Geological Survey (USGS <br />WRI 83-132) treats the Trinidad Sandstone, the Vermejo, and the Raton <br />formations together as one bedrock aquifer. The Raton Formation, which <br />overlies the Vermejo Formation and the coal seam to be mined, is not a water- <br />bearing unit at the site. Because of their permeability and proximity to the <br />coal seam to be mined, the Trinidad and the Vermejo Formations are the water <br />bearing formations of concern with respect to mining and reclamation impacts. <br />Several other bedrock aquifers of regional significance including the Upper <br />Fort Hays Unit, the Dakota Sandstone and the Purgatorie Formation are located <br />stratigraphically below the Pierre Shale which hydrologically separates these <br />units from the overlying Trinidad Sandstone and Vermejo Formations. <br />-1- <br />