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:_ <br />': blue <br />ribbon <br />coal <br />company <br />blue ribbon coal company <br />p.o. box 58 <br />delta, Colorado 8141G <br />13031 874-7561 <br />January 11, 1984 <br />Robert G. Liddle ~~~~A~A~`~ <br />Reclamation Specialist i_~I ry p <br />Colorado Mined Land Reclamation <br />1313 Sherman Street, Room 423 JAid 1 r`; I~~~ <br />Denver, CO 80203-2273 <br />fdINED I_RN9 REC! "V",TIGN f" "' ~„I <br />Re % File ~k C-047-81, Portal bench drainage GCIo. G~pt. of t1~:ul,:i F25o,,..,,, <br />Dear Bob <br />In response to your November 29, 1983, inspection report( part IV, Problems, <br />Recommendations, and Compliance Dates ;k047-83-16), the as built design for <br />the portal bench is being submitted. <br />As observed during Spring and Sucmner 1983, inspections, the portal bench <br />drainage was nearly distroyed by the movement of the edge of the bench. <br />The utility berm down off of the bench was stretched causing leakage of <br />the bench drain, the water line and the sewer line. The middle of the <br />bench dropped lower than the north end where the leaky drain was located. <br />To avoid adding too much weight to the top of the slide and due to the <br />work needed on the north drain the decision was made to drain from the <br />center of the bench. The flexibility, light weight and the long Soint <br />lengths of ADS Corrigated Polyethylene pipe seemed well suited to the job. <br />Sizing was done using the Manning Formula' <br />Q= (Ax 1.486 x R1/3) x S1/2 <br />n <br />Q= flow in CFS, the Peak Flow of 0.92 CFS in areas 2 and 7 was calculated <br />on page 4 of 10 in Appendix C of Blue Ribbon's Permit. <br />A= area of pipe <br />R= hydraulic radios, = A/ wetted perimeter <br />n= coefficient of roughness, (assumed to be similar to steel) n= 0.024 <br />for annular steel culvert, Handbook of steel Drainage and Highway <br />Construction Products, second ed., 1971. <br />S= slope = 0.63% <br />Solving for Q possible in 4 and 6 inch pipes the values of Q4 = 0.82 and <br />Q6 = 2.41 CES were calculated. The 6" ADS plastic pipe was installed in <br />October, 1983. <br />To divert water into the drain inlet a berm was constructed to the south <br />of the drain and part of the drainage protection berm to the north was used. <br />The north corner of the bench is projected to drain to the center but the <br />fill and installation of a ditch was not done during the fall 1983. The <br />• iiiiiiiiiiiii <br />