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• Sediment ditches to capture surface runoff from the RPE East refuse pile <br />• Clear water diversion ditches to capture and divert surface runoff from area above the fill <br />• Sedimentation pond to capture and treat runoff from the sediment ditches <br />Sediment Ditches <br />In accordance with Rule 4.09.3 and 4.09.2(7), the sediment ditches have been designed to safely pass <br />runoff from the 100 -year, 24 -hour storm event. <br />Clear Water Diversion Ditches <br />In accordance with Rule 4.09.2(7), the clear water diversion ditches have been designed to safely <br />pass the runoff from a 100 -year, 24 -hour storm event. <br />Sedimentation Pond <br />The existing two - celled RPE sedimentation pond located northwest of the proposed RPE East will be <br />used to treat runoff from the RPE East and its sediment ditches. Per the Rules, the sedimentation <br />pond contains and treats runoff from the 10 -year, 24 -hour storm event and has an adequate sediment <br />storage volume with periodic sediment removal to effect compliance with water quality regulations <br />of the Colorado Discharge Permit System (CDPS) General Permit for Coal Mining Facilities <br />(CDPHE, 2008). <br />Adequate storage for runoff from both the existing RPE and the RPE East is provided by raising the <br />top of the existing spillway headwall in the manhole located at the head of the discharge standpipe <br />serving the pond. The headwall will be raised six inches to an elevation of 6106.0 to store the runoff <br />from the 10 -year, 24 -hour storm. Larger storms will overtop the headwall and discharge through the <br />existing primary and spillway outlet pipe. The pond area has sufficient capacity to store runoff from <br />the probable maximum precipitation (PMP) event (5 inch rainfall) without overtopping its <br />embankments. <br />Revised April 19, 2010 <br />Revised April 19, 2010 <br />P \Mp1s106 CO \26\06261003 RPE E Permit Mod Support \WorkFilesTermlt Application \Text \E.hibn 82 RPEE design 2011 -07 -21 TR 127.doc 16 <br />