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• Getty Mining Company <br />March 26, 1985 <br />Page 5 <br />to be at elevation 100.0 feet with the water surface in <br />Sedimentation Pond F at the crest of the emergency spillway <br />and the decant system not operational. Runoff Erom the <br />25-year, 24-hour precipitation event of 2.2 inches was calcu- <br />lated using the same runoff criteria as Eor the 10-year storm. <br />The inflow hydrograph for the 25-year, 24-hour rainfall is <br />shown in Appendix 2. Routing of the hydrograph (Appendix 3) <br />indicated that the maximum water surface elevation in <br />Sedimentation Pond F during the 25-year, 24-hour inflow <br />hydrograph would be about 100.5 feet, with a maximum storage <br />of 3.4 acre feet and a maximum discharge of 4.2 cfs through <br />the emergency spillway. Therefore, we conclude that the <br />existing emergency spillway for Sedimentation Pond F will pass <br />the runoff from the 25-year, 24-hour precipitation event <br />without overtopping the pond embankment crest (elevation <br />101.3 feet). This analysis used the extrapolated elevation- <br />capacity curve and, therefore, may be somewhat in error. Our <br />judgment is that this error would not result in overtopping <br />the dam during the runoff Erom the 25-year, 24-hour storm. <br />• SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS <br />Based upon the results of our analyses of existing Sedimenta- <br />tion Pond F, we drew the following conclusions and make these <br />recommendations: <br />(1) The drainage area contributing to Sedimentation Pond F <br />will increase from about 38 acres to about 60 acres <br />upon completion of the proposed Facilities consisting <br />of a new coal stockpile area, screening and crushing <br />building, conveyers, and a loadout. <br />(2) Existing Sedimentation Pond F can completely store <br />runoff (0.95 acre-feet) from the 10-year, 24-hour <br />storm as well as three years of sediment discharge <br />(1.2 acre-feet) from the 60-acre drainage area. <br />(3) eased upon the existing decant and dewatering hole <br />configuration, 90 percent of the 10-year, 24-hour <br />flood inflow hydrograph would be evacuated in approxi- <br />mately 11 days. The detention time for this storm <br />event is about 75 hours. <br />(4) The existing emergency spillway for Sedimentation <br />Pond F would pass the runoff from the 25-year, 24-hour <br /> <br />