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<br /> ~ ii iiiiiiiiiiiiiiiii <br />STATE OF COLORADO RIC Ia PRD D. ~4MM, Gavem nr 999 <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Director <br />MINED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (30$) 866-3567 <br />David C. Shelton <br />Director <br />September 15, 1982 <br />TO: Jim Herron and Brian Munson <br />FROM; Jerry Zimpfer -Sr <br />RE: Powderhorn Coal Company, Discussion of Probable Hydrologic Consequences <br />It is my understanding that Powderhorn Coal Company has some concern with <br />regard to the methods that can be used to estimate the effects of undermining <br />Cottonwood and Rapid Creeks, and the effect of leachate from the coal refuse <br />pile upon flow in the Colorado River. Attached to this memo, you will find <br />an example of these analyses provided by another underground mine in Colorado. <br />Page 29 shows estimation of vertical hydraulic conductivity at the mine, and <br />pages 58 and 59 show the calculation of stream flow depletion using that <br />estimate of vertical hydraulic conductivity. This analysis is based upon <br />assumptions of no subsidence and no natural fractures connecting surface <br />flows to the underground workings. <br />A prediction of the effect of a coal refuse pile upon an adjacent perennial <br />stream is contained on pages 44 to 54. The majority of these pages consist <br />of a water balance used to estimate the amount of deep percolation through <br />the coal refuse pile. This in turn is used to estimate water quality effects <br />on the river (pages 50-54). This particular analysis considers several <br />parameters, but in most cases it is only necessary to consider total dissolved <br />solids (TDS). <br />A copy of those analysis should be forwarded to the applicant. If you or the <br />applicant have any additional questions feel free to ask. <br />JZ:ys <br />cc: Jim Pendleton <br />Fred Banta <br />Attachment <br />