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5~A~TE OF COLORADO DIVISION OF MINERALS AND L~OLOLY Depanmem of Natural Resources 1313 Sherman St., Room ?15 Denver, Colorado 80?03 Phone: (3031 ft66-35L7 rA?:: (3031 83'_-8106 DATE: March 4, 1999 TO: Steve Shuey DIVISION OF MINERALS S GEOLOGY RECLAMATION MINING•SAFETY Bill Owens Governor Greg E Wakher Executive Director Michael B. LOng FROM: Allen Sorenson Drv~swn Drtector .~r.~ RE: 9360 Adit Plug, Homestake Mining Company, Bulldog Mine, Permit No. M-77-215 Reference is made to my memorandum to Harry Posey dated 3/1/99, Harry's memo to you dated 3/3/99 and the telephone discussion you and I had on 3/1/99. Through these memoranda and discussions, the Division has determined that approval may be issued to Homestake to close the valve on the 9360 adit plug to evaluate the integrity of the plug and complete any remedial grouting. Once it is observed that the plug is performing adequately, the tracer and monitoring program detailed in technical revision TR-07 would be initiated. The basis of the Division's determination that the adit may now be plugged, is that the information provided by Homestake through the installation and monitoring of the Creede formation well demonstrates that the ambient ground water condition on the area of the adit plug is contaminated. Thus forcing infiltration of contaminated water by closing the valve on the plug will not cause material damage to the potential uses of the ground water. The purpose of [his memo if to provide a discussion of the ambient ground water condition in the area of the 9360 adit. The preponderance of evidence indicates that the ambient ground water condition in the vicinity of the adit includes contamination by dissolved metals typical of acid rock drainage. The ground water contamination is likely caused by mineralization within the Creede formation. There is a slight possibility that the contamination results from flow through the Campbell Mountain rhyolite of contaminated water present in the flooded mine workings of the Bulldog Mine. However, this possibility is discounted because: It is unlikely that the workings are flooded to an elevation that would create a gradient from the mine pool to the Creede formation well. It is discussed in detail in the reclamation permit file that the likely static mine pool elevation is approximately 9200 feet. The rhyolite is relatively impermeable compared to the contact zone between the rhyolite and the Creede formation. This is demonstrated in the original driving report for the 9360 adit, which states that the made considerable water at the contact, and by the log and yield of the monitoring well, which shows that water was encountered in the well at the geologic contact. It is unlikely that flow through the rhyolite could provide. the yields that the well is producing.