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Rimrock Mine Well Analysis General Information Greg Lewicki and Associates vvas asked by Mark Kerr of Landmark Reclamation, Inc. to review all historical well data and groundwater information to see if groundwater monitoring could be terminated at the Rimrock Mine near Trinidad, Colorado. Considerable data is available for the three wells currently sampled: 1) the Montoya dug well, located downstream of the permit area, 2) well 29-4 located upstream from the permit area and 3) [he USGS well, located immediately downstream of the permit area. Also, the Engleville Mine Discharge, called EMD, has also been sampled on an ongoing basis. The initial sampling vas done as part of the small operator's assistance program administered by the Division to help small operators with collecting baseline permit information. Please refer to the groundwater well map in the approved permit for the locations of all wells. Data is available for depth from ground surface, pH, specific conductance, total dissolved solids; total hardness and all ions required by the Division in its groundwater • testing suite. The Colorado Analytical Laboratory in Brighton, Colorado has conducted all testing since baseline data was gathered in the summer of 1988. They have used EPA approved testing methodology in all of the analyses since testing began. All lab analysis used in this report is included in Appendix 1. Data is available from the summer of 1988 to the end of 1994, although it should be noted that there is a gap in testing from 1990 to 1992 when the process of permitting the mine vas taking place. After a short time in operation, the mine was reclaimed in 1993 and final topsoil replacement and revegetation was done in 1994. The mine only disturbed the permit area west of Engleville Gulch; the eastern part of the permit area was never mined. Data Analysis All wells are located in the Vermejo Formation immediately above the Trinidad Sandstone. The Vermejo is composed of thin bedded shales, sands and siltstones interbedded with many split seams of coal. The Formation is approximately 200 to 250 feet thick in the area and dips approximately 1 ° to the west. The Rimrock Mine attempted to mine the same Starkville seam that was extensively mined in the very large underground mine called the Engleville Mine, whose shallow workings were encountered while opening the Rimrock pit. These workings surround the Rimrock pit on all sides except to the north, where the Starkville seams outcrop in the northern half • ?.07(1) Page9 1/12/95 `Z