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• <br />• <br /> <br />MEMOR4NDU1~1 <br />Tu: Christine Johnston. Itient Gorham. Tm Pendletor. ~~~ ~. <br /> Colorado Division of Minerals and Geoloey <br />- % <br />/// <br />Ci <br /> ~ ~_ <br />FRU~1: R~right Vl'ater Engineers, Inc. for Mountain Coal Comparr< ~ <br />( - <br />~~/ <br />~ <br /> ~. ~~ , <br />.~' <br />DATc: September 18, 199 ~ ' <br /> 1 ~~ <br /> <br />RE: <br />Basis for Vb~-E~s Estimate of 1~ to .0 Acre-Fe v <br />et of Average <br />Anna.=1 <br /> Hydrologic Impacts Due to Proposed 64inine in Apache Rocks Pe.;mit <br /> Revision .Area <br />In response to our meeting with you on September 11 regazdine the Apache Rocks permit <br />revision area for the West Elk Mine and the various questions posed by CDMG regazding <br />probable hydrologic consequences, WWE has prepazed this memorandum to summarize <br />the basis for the estimate of 15 to 20 acre-feet of average annual hydrologic consequences <br />(see page 2.05-156) that could result from mitring in the Apache Rocks permit revision <br />azea. From the outset, it is important to note that: (1) 95 percent of this water «ill <br />ultimately be returned to either the Dry Fork of Minnesota Creek or the North Fork <br />Gunnison River and (2) MCC has ample water tights on both the Dry Fork and North <br />Fork to cover its out-of-priority diversions, if relevant. As demonstrated with the <br />following calculations, the projected impact of 15 to 20 acre-feet annually is <br />conservative. <br />There aze four broad categories of hydrologic changes which could result: (1) springs. (~) <br />streams, (3) groundwater, and (4) stock ponds. Each of these is addressed in turn. as <br />follows: <br />IMPACTS TO SPRINGS <br />1. From page 2.04-79, there aze 69 springs in the pemrit azea with flow rates ranging <br />from 0 gpm to 120 gpm, with an average of 3 gpm. <br />2. Sixty-four of the 69 springs have at least 300 feet of overbtuden above the highest <br />seam to be mined. This is important because the combined depth of the fracture zone <br />and caved zone is, conservatively, 270 feet. <br />U <br />Z <br />H <br />[Y <br />W <br />W <br />Z_ <br />V <br />Z <br />W <br />W <br />H <br />Q <br />3 <br />H <br />2 <br />V <br />3 <br />. I 3. As per Table 12 on page 2.04-81, there aze 14 springs in the .apache Rocks permit <br />revision azea. The average springtime flow is 5 gpm while the average autumn ilo« <br />