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iii iiiiiiiiiiiiiiii <br />STATE OF COLORADO <br />DIVISION OF MINERALS ANO GEOLOGY <br />Depanmem ul Nanual Kesuurces <br />111 3 Sherman SL. Knrnn ' I i <br />Denver, CnlumAo H11'LO} <br />Vhune'. LJO SI 866-}567 <br />FA%:1]031 HJ2~810h <br />September 23, 1999 <br />Carla 1. Lenl:ey <br />Colorado Department of Public Health and Environment <br />WQCD-WQP-B2 <br />4300 Cherry Creek Drive South <br />Denver, CO 80246-1530 <br />Re: Information, Discharge Point O1 OA, Colowyo Coal Company L.P. <br />Deaz Ms. Lenkey: <br />DIVISION OF <br />MINERALS <br />GEOLOGY <br />RECLAMATION <br />MINING-SAFETT <br />Bill Owens <br />Governor <br />Greg E Walther <br />ESeculrvc Dneclor <br />Michael B Lung <br />Division Dnenor <br />This information is provided to you in response to your telephone call eazlier this month <br />concerning pond design information, and information in inspection reports azound April 12, 3999, <br />with regazd to Dischazge Point OlOA at the Colowyo Coal Company L.P. <br />Dischazge Point OlOA is associated with the East Taylor Pond (Pond). Design information is <br />contained in Appendix J, Exhibit 7, of Permit C-81-O19. The Sediment, Erosion, Dischazge by <br />Computer Aided Design (SEDCAD) program by Civil Software Design was used to model the <br />pond. A "worst-case" situation was selected to model the pond. This "worst case" represented <br />"closure" of the West Pit, a time when the watershed would consist of the maximum area of <br />disturbance and the greatest amount of area unprotected by vegetation. The demonstration <br />included a watershed of 918.6 acres, of which 126 consisted of baze topsoil that had been seeded <br />(initial reclamation) and the rest with some sort of vegetation cover. Storm events of l0-yeaz, 24- <br />hour (1.8 inches of rain) and 25-year, 24-hour (2.3 inches of rain) were used in the design. The <br />demonstration is for a pond that dewaters automatically. In automatic dewatering mode, the pond <br />is designed to dewater through weep holes down to an elevation of 6944.0 feet (static pool level}. <br />The design maximum level of collected sediment in the pond is up to 6939.78 feet. The elevation <br />of the invert of the primary spillway riser is at 6952.0 feet. The following table summarizes the <br />demonstration with regazd to Peak Sediment Concentrations (mg/l) and Peak Settleable <br />Concentrations (mUl). <br />l0-Yeaz, 24-Hour Event <br /> Peak Sediment Concentration (mg/l) Peak Settleable Concentration (ml/I) <br /> <br />[n: 314640 141.77 <br />Out: 78491 0.00 <br /> <br />25-Year. 24-Hour Event <br />[n: 319047 144.55 <br />Out: 93 ~ 76 0.01 <br /> <br />