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TECHNICAL MEMORANDUM <br />To: Bill Lyle <br />Date: January 3, 2004 <br />Page 12 <br />~ east side of the pit), and from seeps and springs that were controlled by the local <br /> geologic structural features. Currently, the discharge of ground water from the <br /> bedrock aquifer is localized, again, due to the hydrogeologic relationships and <br /> engineering controls that have been implemented. <br />' • Current backfill ground water concentrations are equal or less than the pre-mining, <br /> shallow ground water chemistry in the bedrock aquifer. The concentration of TDS, <br /> sulfate, iron, and manganese in the West Pit backfill are statistically less than the <br />' average pre-mining concentrations in the shallow bedrock aquifer. Current fluoride <br /> concentration in the West Pit backfill is statistically indistinguishable fpre-mining <br /> conditions. <br /> REFERENCES <br /> Benson, R.G. 1997. Detachment fault-related mineralization in a rift setting at the San <br /> Luis gold deposit and Sangre de Cristo Mountain, Alamosa, Costilla, and Saguache <br />' Counties, Colorado. Unpubl. Ph.D. dissertation. Colorado School of Mines. <br /> Miller, W.R., J.B. McHugh, and A.L. Meier. 1995. Calculations of pre-mining <br /> geochemical baselines at three stream junctions for Wightman Fork and Cropsy Creek <br />' neaz Summitville, Colorado. Posey, H.H, Pendleton, J.A., and Van Zyl, D. (editors}; <br /> Preceedings: Summitville Forum'95; Colorado Geological Survey Special Publication <br /> 38, Denver, Colorado, p. 58. <br /> Technical Revision 15 -Response Plan. 1998. Supplemental Monitoring at West Pit, <br /> BMRI's San Luis Project, Permit No. M-88-1 ]2. November. <br /> <br /> Technical Revision 26. 1999. Water Management in the West Pit Area, San Luis Project, <br /> Costilla County, Colorado. Report submitted to the Colorado Division of Minerals and <br />' Geology. March. <br /> Runnells, D.D., Shepherd, T.A„ and Angino, E.E. 1992. Metals in water: Determining <br /> natural background concentrations in mineralized areas. Environmental Science <br /> Technology, v. 26, p. 2316-2323. <br /> Wallace, A.R. and S.J. Soulliere. 1996. Geologic Map of the Ojito Peak Quadrangle, <br /> Costilla County, Colorado. U.S. Geol. Surv. Misc. Field Studies Map, MF-2312-B. <br /> <br /> <br /> <br />O~Nrolec«X212-rrexmrmr(+m-,luis)Uunluis4r-IBnrrgln'ynemirte nearpirdoc <br /> <br />