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TO: FROM DATE: RE: MEMORANDUM Dave Berry and Susan McCannon Colorado Division of Minerals and Geology Wright Water Engineers, Inc. Jon Jones, Gary Witt, and Jonathan Kelly February 18, 1998 iiiiiiiiiiiiiiiiiu RECEIVED f ~- ._ _ IJ~(1 Division of Minerals & Geology Key Points Relative to Bear No. 3 Mine Observed Inflows The purpose of this memorandum is to outline key points relative to Bear No. 3 Mine observed inflows and Mountain Coal Company's (MCC) concurrent water management activities. This memorandum is designed to supplement the geological and geotechnical analyses presented to the Colorado Division of Minerals and Geology (CDMG) on December 18, 1997 and the water quality and isotope analyses presented to CDMG on January 21, 1998. To aid this memorandum, the attached tables and graph have been prepazed based on information from Bear Coal Company's 1995 and 1996 Annual Hydrology Reports (AHRs). 1. The Beaz No. 3 Mine inflows were first noticed in June 1995, one-and-a-half years before MCC began to store ]azge volumes of water m the Northwest (NW) Panels sealed sump on November 11, 1996. 2. Prior to November ] 1, 1996, the only water that accumulated at the north end of longwall panels 1NW through SNW was ambient groundwater inflows, estimated at less than 10 gallons per minute (gpm), and mine process water. Mine process water was allowed to drain downgradient to an operational sump at this location where the water was then pumped out of the mine. After longwall panels 1NW through SNW were sealed in May 1995, the only water that contributed to this location was the ambient groundwater inflows of less than 10 gpm. 3. Seepage out of the NW Panels prior to November 1996, if any, would have been insigniScant due to the small volume of water, hydraulic head, and flow-through azea within MCC's NW Panels. Even if there were substantial secondary porosity in the nnm~ned coal block between the mines, there was an insufficient supply of water in the NW Panels to be the source of the observed, continuous 18 gpm, reported by Beaz in their 1996 AHR. Furthermore, MCC's water management practices of cycled pumping of accumulated water in the operating sections updip of Beaz, would not yield constant inflows such as those observed in the Beaz No. 3 Mine during 1995. 4. The reported inflows for the period from June 1995, when inflows were first observed in the Bear No. 3 Mine, through December 1995 were I S gpm. Based on Bear's responses to MCC's questions dated December 19, 1997, this inflow rate was based on only one or two measurements (response #12). Beaz's 1995 AHR indicates that these inflows were consumed by mining operations and no water was dischazged to the North Fork. Average flows during 1996 were approximately 30 gpm and the mine water was dischazged to North Fork. The discharge values shown in Table 1 are a conservative representation of mine inflows since part of the mine inflows was consumed by mining operations prior to dischazge. Thus, Beaz No. 3 U Z W W _Z C7 Z W W Q 3 H 2 C7