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. <br />~ iii iiiiiiiiiiiu iii <br />999 <br /> <br /> <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone. (303) 866-3567 <br />FA\: (303) 832-8106 <br />June 2,2000 <br />To: Tom Schreiner <br />From: Harry Posey ' <br />Subject: Review: Response to Comments, arge Corp., Tanabe Pit, M-2000-002 <br />[ have reviewed the Operator's Respons to Objector Comments and Response to DMG <br />Comments letters dated May 24, 2000, received May 25, 2000. <br />DIVISION OF <br />MINERALS <br />GEOLOGY <br />R E C L A M A T I O N <br />MINING•SAFETY <br />Bil I Owens <br />Governor <br />Greg E. Walther <br />Execwive Dveaor <br />Michael B. Lang <br />Division Dvecror <br />Please recall that my general comments indicated that the Operator should famish current <br />information on the location and chemical conditions of contaminant plumes in the alluvial <br />aquifer related to the Rocky Mountain Arsenal. The operation is proposed to occupy and remove <br />part of the alluvial aquifer that was apparently contaminated at least in part by RMA. My general <br />concerns were whether pumping of the alluvial groundwater would have the potential to redirect <br />groundwater from the treatment wells operated at the Arsenal and whether contaminants <br />potentially within the pumped water would be identified and handled adequately. <br />The response indicates that DIMP is the only non-native material with the potential to exceed <br />water quality standards. <br />The Operator's response demonstrates that the drawdown cone in the alluvial water, which will <br />be generated by pit de-watering, will cross into the two high DIMP areas adjacent to the <br />proposed pit. Concentrations of DIMP in these zones exceed water quality standards by several <br />times in some wells. Actual concentrations at each point within the high DIMP zones cannot be <br />known, but concentrations both above the highest value and below the lowest value within the <br />DIMP plume would not be unexpected. Considering the hydrology and DIMP concentrations, <br />there appears to be a chance, albeit small, that DIMP concentrations that might report to the <br />dewatering trench could exceed the standard. Once the trench water is pumped from the Tanabe <br />pit and mixed with existing pit water off site, concentrations would be extremely diluted. <br />Moreover, contact with sunlight would be expected to break down the DIMP. <br />• • <br />Whether DIMP is to be added to the list of monitoring parameters under the current CDPS <br />permit has not been decided, though the operator has been working through the issue with the <br />