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• . iii iiiiiiiiniiiiii STATE OF COLORADO DIVISION OF WATER RESOURCES WATER DIVISION FOUR Officz of thz State Engineer Departmem of Natural Resources 1540 E. Niagara P.O. Box 456 Montrose, Colorado 81402 Phone (970)249-6622 Fax 1970)249-8728 http://water.state.co. us/defau It.htm Joseph J. Dudash Environmental Protection Specialist Division of Minerals and Geology Department of Natural Resources 1313 Sherman St., Room 215 Denver CO 80203 ~~~ ~.~iew ~~y0' RECEIVED ~' tal6 ~ DEC 21 2000 Bill Owens Governor Division of Minerals and GealogY Greg E. Walther Executive Director Hal D. Sintpsan, P.E. State Engineer December 21, 2000 Wayne 1. Schieldt Division Engineer Subject: Comments regazding Bowie No. 2 Mine (permit No. C-1996-083) Dear Mr. Dudash: Thank you for your letter of October 23, 2000 announcing the permit application by Bowie Resources for the expansion of their mine. The purpose of this letter is to provide comments pertaining to the subject coal mining permit relevant to issues surrounding the effect mining activity may pose on the safety of the Bruce Park dam (a.k.a. Tenor Creek Reservoir). As described in the application, activity associated with the coal mining process potentially creates two physical ground motions, subsidence or vertical displacement of the existing ground surface, and seismic waves as a result of the ground subsidence. If ground displacements or ground motion of sufficient magnitude occurs in proximity to the Bruce Pazk dam, integrity of~the structure may be jeopardized. The Bruce Park dam is categorized a Class I dam as defined by the Rules & Regulation for Dam Safety. The Class I designation indicates potential for loss of life is probable in [he event the dam fails. Bowie Resources claim in their application the "Terror Creek Reservoir is outside the angle of draw cf the mine workings." y~'hile the revised mine plan s::cws the theoretical projection of draw on the ground surface does not encompass the Bruce Pazk dam, the map shows the perimeter is within approximately 4000 feet of the main embankment. Even though experts agree the 4000-foot distance does not pose a serious added risk to the dam, some risk does still exist. Therefore, I concur with Bowie Resources' contention stated in the application that "the embankment could possibly be damaged by mining induced seismicity." The application also indicates, a detailed subsidence study will be completed prior to mining within a mile of the structure, but mentions nothing regarding instrumentation and monitoring of the dam. I feel strongly instrumentation be installed and a monitoring plan be in place before mining progresses inside a 1 mile radius ofthe reservoir in order to have baseline information available for comparison. The instruments shall measure physical responses of the dams and the foundations due to movements or seismic forces that may potentially exceed the available strength of materials comprising the manmade embankments or natural substrata. The monitoring plan must provide a