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iii iiiiiiiiniii iii 999 STATE OF COLORP~DO DIVISION OF MINERALS AND GEOLOGY Department o(Natural Resources 1313 Sherman St., Room 215 Denver, Colorario 8020] Phone: 1]031 866 3 567 FA%: I]031 8]2 5106 DATE: January 5, 1995 TO: Harry Ranney FROM: Jce Dudash C~ RE: West Pond and Fast Pond, Hydrology and Sedimentology, National King Coal, Permit No. C-81-035 ~~ ~~~~~ DEPARTMEIYI' OF NATURAL RESOURCES Roy Romer Governor lames S Lochhead Execmrve Director Michael B. Long Division Direcror This memo is to update or clarify the memo of October 10, 1994. In a discussion with you in late December of 1994, you told me that the 10 year - 24 hour event is 2.2. inches and the 25 year - 24 hour event is 2.6 inches, Lather than the 2.3 inches and 2.9 inches, respectively, that I had used. Therefore, I reran Sedcad and the following are the differences. For the west pond, the peak settleable solids from the 10 year - 24 hour discharge is .31 mUl, rather than 2.03 mUl. So the discharge is in compliance. Also, the maximum elevation of the pond water fora 25 year - 24 hour event is 7390.04 feet, rather than 7390.3; as previously stated. This is, for all practical purposes, 1 foot below the embaLilmLent top, which would put it barely incompliance. Finally, the 10 year - 24 hour event maximum elevation is right at the emergency spillway, similar to the previous analysis, so my comments in the October 20, 1994 memo still apply. In the memo, I want to elaborate on the hydrologic performance of the east pond. There is discharge out of the primary fora 10 year - 24 hour event. However the peak settleable solids is 0 mUl, so the discharge is in compliance. There is no discharge out of the emergency spillway for either the 10 year - 24 hour event or the 25 year - 24 hour event. Finally, the maximum elevation of the pond water from a 25 year - 24 hour event is 2:5 feet below the embankment top, well in compliance. M:\OSSVmmlRinnry.jjd