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STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />D O L O <br />R N OO <br />Denver, Colorado 80203 I <br />F <br />Phone: (303) 866-3567 RECLAMATION <br />FAX: (303) 832-8106 MINING <br /> <br /> SAFETY <br /> Bill Ritter, Jr. <br /> Governor <br /> James B. Martin <br /> Executive Director <br />INTEROFFICE Loretta E. Pineda <br /> Director <br />MEMORANDUM <br />TO: Janet Binns <br />FROM: Kent Gorha4? <br />SUBJECT: DP-1 Pond Riser Revision, # C-81-018 <br />DATE: April 13, 2010 <br />I reviewed the SEDCAD modeling for the proposed change to the DP-1 <br />pond riser to include a 2" weep hole, a 24 inch riser and a 17.5 inch slipline <br />through the barrel. The operator has included design runs for the 10-year, <br />the 25-year, and the 100-year storm events. The modeling runs appear <br />complete and representative for the site. Modeling estimates that the 10- <br />year storm event will be treated to be equal to of less than the effluent <br />limitation for sediment. The 25-year storm and the 100-year storm both <br />pass safely through the pond without overtopping the embankment or <br />overwhelming the emergency spillway. <br />In accordance with Rule 2.05.3(4)(a)(ii)(c), please have the operator <br />describe in the permit text how the gate on the weep hole will be <br />operated, under what conditions will it be closed, if any, and a <br />commitment to sample all manual discharges in accordance with the <br />approved CDPS permit. This permit text can be added to existing page <br />IV-39. <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines