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March 7997 EFC/ Sou/hReld Mine Adepuecy Responses • 1 <br />TECHNICAL REVISION NO. 11 <br />ADEQUACY RESPONSES TO STIPULATION NO. 19 <br />Stipulation No. 19: <br />Within 30 days ,EFCI will re-evaluate the engineered designs for Pond 3 to accommodate sediment <br />generation from the entire watershetL In addition, Map 11 will lx modified to reflect hydraulics <br />associated with the reduced watersheds <br />Response: <br />Annual sediment yield was re-evaluated for both Ponds 1 and 5 using SEDCAD+ which utilizes <br />the Revised Universal Soil Loss Equation (RUBLE). The methodology and assumptions used <br />to re-evaluate the ponds aze outlined on Revised pages 14Ra - 14Rd. <br />SEDCAD+ results indicate annual sediment yields for the Pond 1 drainage area (7.5 acres) of <br />0.52 ac-ft. The actual sediment capacity for pond 1 is 1.06 ac-ft. Consequently, Pond 1 provides <br />[wo years of sediment capacity. It should be noted that maximum sediment level corresponds <br />to elevation 6114.00, which is well below the invert of the inlet culvert. <br />The annual sediment yield for the Pond 5 drainage area (32 acres) is 0.46 ac-k. The actual <br />sediment capacity Eor Pond 5 is 0.78 ac-ft. Consequently, Pond 5 provides 1.7 years of sediment <br />apaci[y. <br />The sedimentation Pond No. 1 Design Map, (Map 21), Sedimentation Pond No. 5 Design Map, <br />(Map 24), and Exhibit 19, Drainage and Sediment Control Plan have been revised to reflett the <br />new sediment calculations. Revised permit materials are provided with these responses for <br />insertion replacement in the EFCI Permit Application document. <br />O[her Matters: <br />Page 10 of Exhibit 19, Drainage And Sediment Control Plan indica[es that the thickness of the <br />riprap layer will be 1.25 times the D„ size. In addition, EFCI will commit to placement of a <br />rock filter blanket below the riprap. The rock filter blanket will consist of uniformly graded <br />durable rock material with a [hickness of six to nine inches. Page lOR has been revised to <br />reflex the installation of a rock filter blanket for riprap installations. <br />~,.aw7rw.iiw~o <br />~~ <br />