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';`~f~ ,'.' FIOV-15-19?1 1a~29 FP.01I <br />:.,' <br />,~,, ~ . <br />November 14, 1991 <br />Ms. Kathleen G. Welt <br />' Mountain Coal Company <br />P.O. Box 591 <br />Somerset, Colorado 81434 <br />GEubIEST GnLpEhl <br />CEOWEST <br />Golden, Inc. <br />TO 03039295595--1527 <br />RE: HYDROLOGY CALCULATIONS FOR PROPOSED COA1. STORAGE PAD <br />Dear Kathy: <br />P.ea; ii ~;~i',; <br />~„ ~ , , ,~ <br />r„i ~ <br />t.i, i <br />!,. <br />`~. <br />_.~ _ <br />I <br />d <br /> <br />y,~ <br />A <br />The purpose of this letter is to respond to your request for an analysis of the surface water hydrolvyy~ <br />at the West Elk Mine with respect to the construction of•.a proposed coal storage pad. We hc~va <br />calculated the changes in peak disrharge and runoff volume routed to the existing sedimentation pond <br />and determined the effect that these changes will have on the pond's storage capacity. The followirg <br />,.. <br />Is a report of our findings, includi, ly all assumptions and calculations that were used. <br />SUMMARY OF RESULTS <br />ii <br />An analysis of the additional storm water runoff due to constrtction of the proposed coal storage pac, , <br />~•, <br />.shows that there fs sufficient storage capacity in the existing sedimentation pond to contain all runoff <br />routed to the pond as tha result of a 10-year, 24-hour pre~ipitatlon event. Construction of the pad will . <br />~. <br />increase the peak d'+scharge of storm water runoff to the sedimentation pond,by approximately, 2.9 <br />cubic feet per second (ufs) and increase the volume of Inflow to the pond by 0.16 acre-foot. `MTh? <br />resulting water surface elevation in the sedimentation pond would be 6,093.8, which is 0.03 foot below <br />r <br />the elevation of the emergency spillway crest. i <br />ASSUMPTIONS <br />Values for hydr~to~ic data pertaining to the existing sedimentation pond such as peak Inflow, total <br />water inflow and total sediment volume inflow during the i 0-year, 24-hour precipitation event were taken <br />from Hydrologic Data, Runoff Fond #2 by Merrick and Company, 1980. This reference was also used <br />to determine total pond capacity and elevations for [he emergency spillway crest, sediment cleanout <br />and water level versus capacity comparisons. <br />9ns.Onc /,~0 ~~Stt~+cn <br />'nvt orn,nerce Censer, Snile 2006 • 175 \Vact 200 Somh Salt Lake City, Utah 84llt • (8011 359-3059 <br />rnro, e n ~ <br />