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Mike Boulay <br />-2- May 3, 2012 <br />in its present alignment and configuration. To date there have been no other comments or <br />objections by any other state or federal agencies notified of the proposal. <br />With our proposed decision, the Division will need to update and revise the Findings document <br />with regard to Diversions and Conveyance of Overland Flow and Stream Channel Diversions. To <br />facilitate preparation of the Findings document please check and ensure that the design <br />information for Coal Canyon prepared in 1996 is accurate and reflects the configuration proposed <br />to be left as a permanent post- mining feature. The Coal Canyon Runoff and Drainage Design is <br />contained in Appendix 13 -2 of the PAP. From the design information it shows that the diversion <br />drains a watershed greater than one square mile and has been appropriately designed to pass <br />safely the peak runoff of a 100 -year, 24 -hour event. Please add this description and any other <br />distinguishing features of the Coal Canyon alignment to page 14 -13 where Appendix 13 -2 <br />is referenced. <br />SCC: Permit page 14 -13i was added in order to address the design of the current Coal Canyon <br />runoff and drainage. <br />4. DRMS: For the North Portal Reclamation Ditches SEDCAD demonstration beginning on page <br />14 -6 -118, the curve numbers for the Upland and Reclaimed Areas have been changed from the <br />previously approved curve numbers. Please provide the rationale for the change in curve <br />numbers. <br />SCC: The curve numbers were reverted back to previously approved curve numbers as shown <br />on page 14 -6 -118. <br />5. DRMS: For the North Portal Reclamation Ditches SEDCAD demonstration SCC provided a <br />Flow Summary Sheet. Please also provide the Structure Networking and Structure <br />Summary pages from the SEDCAD printout. <br />SCC: Please see revised SedCad demonstration beginning on 14 -6 -118 showing the Structure <br />Networking, and Structure Summary pages for both the West and East Flows. A SedCad error <br />was discovered while re- evaluating the network for the West Flow portion of the North Portal. <br />The old network lists a flow of 6.96 cfs coming from the CRDA2 -East Upper Diversion ditch. This <br />flow should be 17.5 cfs. Therefore, all of the ditches on the West Side were revised. SedCad is <br />not able to handle large flows and steep slopes. To be consistent, all ditches were designed <br />using Manning's Equation in Excel, and rip rap is also sized using excel. <br />One ditch was added to the West Flow network, ditch D13. Due to the low curve number (62) <br />there is minimal flow in the ditch, such a small flow in fact that neither SedCad or Excel was able <br />to provide a ditch size. Therefore, the ditch was assigned a generic ditch size that will be more <br />than adequate to carry the minimal flow. <br />As a note, ditch D10 was realigned to follow the in -place berm. The berm will remain in place as <br />a permanent feature. After a field visit on April 25th, it was evident that routing the flow to the <br />berm was a logical way to construct the ditch. This re -route increased the slope from 2.0% to <br />2.5 %, with pit run being specified for channel protection. <br />From the previously mentioned site visit, it was determined that another ditch, J3 -J3, shown on <br />Exhibits 9C and 60 flowing from reclaimed topsoil stockpile #9 into coal creek needed to be <br />designed. The design is included as page CRDA2 -7c. <br />Ditches H1, J1, J2, El were redesigned, the side slope changed from 2.0 H: 1V to 1.5H:1V. <br />Exhibit 53 was revised due to the change in side slope, and ditch J3 -J3 was added. <br />