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Mr. Roy Karo Seneca Coal Company June 28, 2005 Page 2 ponds from spoil springs appears to be under-estimated in the SEDCAD demonstrations. A base-flow, peak discharge of .07 cfs was used for spring flows into the ponds at both pond locations. Recent AHR information indicates that spoils springs discharge significantly larger flows to these ponds, particularly to Pond 004. Spoils Springs # 1 and # 2 flow to Pond 004 and Spoils Spring # 9 flows to Pond 008. In a wet year, Spoils Spring #1 has been documented to flow at nearly 650 gpm. Flow from Spoils Spring #1 in Apri12004 was .64 cfs. Ten years of data for Spoils Spring #9 shows an average flow of 41.1 gpm or .092 cfs. Furthermore, DMRs indicate that these ponds discharge throughout the yeaz. During the period of snowmelt in the second quarter 2004, both ponds had an average dischazge of .60 cfs, which is higher than the peak discharge exiting either pond generated by the 10-yeaz, 24-hour precipitation event. The initial permanent pools for the SEDCAD models for both ponds have been set at the principal spillway elevations. Both Pond 004 and 008 have the minimum required one- foot difference in elevation from the principal spillway to the invert of the emergency spillway. The models do not appeaz to adequately account for combined spoil spring inflow, snowmelt runoff, and the 10-yeaz, 24-hour storm event. To ensure that the principal spillway pipes are adequate to handle springtime base-flow and spoil springs inflow combined with the 10-year, 24-hour precipitation event, the Division recommends that the principal spillways be lowered or alternatively the emergency spillways be raised to allow for additional containmentitreatment capacity for the 10-year, 24-hour precipitation event. Please revise the SEDCAD demonstrations and Exhibits 7-21 and 7-17D accordingly. Please include 10-year, 24-hour and 25-year, 24- hour SEDCAD demonstrations for the spillway reconfigurations. The Division recognizes that the sedimentology could change from how the pond was originally designed for active mining disturbance. However, a slight lowering of the principal spillway elevation should not require a revised sedimentology demonstration, given the permanent pool vo]umes and the associated storm runoff estimates. 4. Upon completion of construction, please submit certified as-built reports for Sedimentation Ponds 004 and 008. If you have any questions please call me. Sincerely, 1~; P. ~5~t.~ Michael P. Boulay Environmental Protection Specialist C: Sandy Brown