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a~~ <br />1~~. <br />October 17, 1996 <br />Ms. E. Cosby <br />Page 6 <br />TABLES <br />SEDIMENT POND DATA SUMMARY <br /> Gulch A Pood Gulch A Pood <br /> (E:fisting Cooditions) (Post- Mine Conditioty) <br />Peek Flow Conditions (cfs): <br />Pond Inflow 11.41 3 f.25 <br />Pond Outflow 3.10 4.78 <br />Peak Settleable Concentration (mg/I): <br />Pond Inflow 457.14 148.07 <br />Pond Outflow 0.00 0.00 <br />Peak Sta a (H) 6619.0 6619.8 <br />4.0 CONCLUSIONS <br />It is suggested that the post-mine condition be evaluated as the worst case scenario for each of the Colowyo <br />ponds. As shown in Table 5, the run-off volume from the post-mine condition is nearly twice the existing <br />condition, yet both conditions yield no sealable solids from the pond discharge during the 10-year, 24-hour storm <br />event. Designing for the post-mine condition would result in a more conservative and economical design <br />eliminating the need for modifications as future conditions change. <br />Please contact the undersigned should you have any questions or comments about the analyses performed. <br />Sincerely, <br />TertaMatrix [nc. <br />~~ ~/ice~rw~ <br />Kevin Kammerzell <br />,P r/~/oj ect~Engine)er <br />-t'~JThomas~E. ' h, P.E. <br />Senior Engineer <br />cc: Juan Garcia, Colowyo Coal Company <br />File <br />