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:~ • MEMORANDUM TO: FROM: DATE: RE: Christine Johnston, Kent Gorham, Jim Pendleton Colorado Division of Minerals and Geology R'right N'ater Engineers, Inc. for Mountain Coal September 18, 1995 • iiiiuiiiiuiiiiiii Basis for W WE's Bstimate of ] 5 to 20 Acre-reef of Average Annual Hydrologic Impacts Due to Proposed Mining in Apache Rocks Permit Revision Area In response to our meeting with you on September 11 regazding the Apache Rocks permit U Z revision azea for the West Elk Mine and the various questions posed by CDMG regazding probable hydrologic consequences, WWE has prepazed this memorandum to summarize ~ the basis for the estimate of 15 to 20 acre-feet of average annual hydrologic consequences W (see page 2.05-156) that could result from mining in the Apache Rocks permit revision Z area. From the outset, it is important to note that: (1) 95 percent of this water will V ultimately be returned to either the Dry Fork of Minnesota Creek or the North Fork iZ Gunnison River and (2) MCC has ample water rights on both the Dry Fork and North ~ Fork to cover its out-of-priority diversions, if relevant. As demonstrated with the W following calculations, the projected impact of 15 to 20 acre-feet annually is 3 conservative. H- There are four broad categories of hydrologic changes which could result: (1) springs, (2) _ V streams, (3) groundwater, and (4) stock ponds. Each of these is addressed in turn, as p~ follows: 3 IMPACTS TO SPRINGS 1. From page 2.04-79, there aze 69 springs in the permit area with flow rates ranging from 0 gpm to 120 gpm, with an average of 3 gpm. 2. Sixty-four of the 69 springs have at least 300 feet of overburden above the highest seam to be mined. This is important because the combined depth of the fracture zone and caved zone is, conservatively, 270 feet. 3. As per Table 12 on page 2.04-81, there are ]4 springs in the Apache Rocks permit revision area. The average springtime flow is 5 gpm while the average autumn flow