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ENVIRONMENTAL PROTECTION AGENC Y !-lEGION VIII SUITE <)00. 18€on L INCULN STREET OENVER. COLORADO A0203 October 29, 1971 Mr. R. G. Burnett Chief, Engineering Division Department of the Army Omaha District, Corps of Engineers 7410 U.S. Post Office and Court House Omaha, Nebraska 68102 Dear Mr. Burnett: In accordance with your request of September 8, 1971, the Environ- mental Protection Agency has reviewed the draft environmental state- ment for Bear Creek Dam and Lake, Colorado. The following comments are offered for your consideration in prepar- ing the final statement: 1. The extent of the potential acid mine drainage should be further defined. There are apparently many abandoned coal mines in the vicinity of the proposed reservoir, but only several mines within the project boundaries. Measures that would be taken, if any, in regard to prevention of pollution from mines outside the project boundaries should be described. Preventing water from entering the mine and the rapid removal of that water which does enter the mine have been demonstrated as sound methods of reducing acid pollution. Permanent flooding of deep mines has also been found to prevent acid formation. Air sealing of mines to prevent acid mine drainage pollution has been practiced since the 1930's. It is based on the theory that if oxygen is excluded from the mine, the oxida- tion of pyrite and ferrous iron cannot occur or will be reduced. This method has not generally been successful largely because of the difficulty in preventing the entrance of air to the mine. For example, a significant amount of air can enter a mine through the overburden because of baro- metric changes (breathing of mine). Adequate controls should be placed on all mining in the reservoir drainage area to assure that reservoir water quality will be suitable for its intended uses.