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~ S • ~ III III III IIIIIII III STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Depanmern oS Natural Resources I J 1 J Sherman SL, Roam 215 Denver, Colorado 80203 Phone: IJOJI 866-7567 FA%~ (3071 832-8106 DATE: April 15, 1997 T0: Bruce Humphries, Harry Posey and Berhan Keffelew FROM: Jim Stevens JG~ ~~~ DEPARTMENT OF NATURAL RESOURCES Roy Romer Govemur tames 5. Lochhead Execulrve DueUOr Michael B. Lang D rvision Direuor RE: Review of the 1993 and 1994 HCI reports provided to and by CC&V As Bruce requested, I reviewed the above referenced reports. Much data was introduced in the reports that I did not attempt to verify, given the limited time available. The intent of the HCI effort was to demonstrate that the mine would have no significant effect on the quality and quantity of water discharging from the underlying Carlton Tunnel. While I don't have any serious quarrel with the approach taken by HCI to do this, the reports do not entirely satisfy the Division's concern as to the potential impacts of acid drainage from the Cresson Pit and waste dumps on the ground and surface water in the area of the mine. The HCI reports provide the basis for CC&V's argument that all drainage from the pit and the waste dumps at the Cresson Mine either is neutralized by contact with the native rock in the caldera as that drainage, along with all the ground water draining to the Carlton Tunnel, is forced to make its way down to the level of the tunnel or is neutralized by the Carlton Tunnel discharge itself . The HCI reports do not attempt to argue that acid rock drainage will not result from the exposure of sulfide rich materials in the pit, and presumably the waste dumps. The reports simply focus on the neutralization capability of the wall rock and Carlton Tunnel discharge on that drainage and the apparent result, ie. the lack of acid character of the Carlton Tunnel discharge. One is left with the impression that the quality of the Carlton Tunnel discharge is the only groundwater concern in the area of the mine. This is not necessarily true. There is ground water found in the caldera at levels above the Carlton Tunnel, groundwater associated with perched aquifers or to be found in areas isolated from the drainage effects of the Carlton Tunnel. If the groundwater in such circumstances should also have a quality allowing present or future beneficial use, an effort to require that the operator protect such water from the adverse impacts of acid drainage from the Cresson Pit and waste dumps would be appropriate. So far as I can determine from the limited information available to me, however, the shallow ground water in