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the inlet of Ditch NHN -002 North located approximately 160 feet from the principle spillway, still a <br />sufficient distance to prevent short circuiting. This assertion is reinforced in the approved permit <br />in Appendix 2.05.3(4), as stated on page 6, "gated principle spillways, as designed for all three <br />ponds, prevent short circuiting ". <br />5. Please include design information for the emergency spillway channel to indicate the <br />flow depth and demonstrate adequate embankment height to ensure l' of freeboard, as <br />required by Rule 4.05.9(7)(d). <br />WFC Response: The four SEDCAD runs for the as -built pond show no discharge through the <br />emergency spillway, therefore no emergency spillway flow is indicated for use in calculating <br />freeboard. The minimum freeboard resulting from these four SEDCAD runs occurs during the <br />25yr -24hr weep holes closed case, where the peak pool stage elevation is 5,676.62 ft. This <br />provides for 2.88 feet of freeboard to the top of the dam at 5,679.5 ft. The emergency spillway has <br />been built to the elevation of 5,677.5, two feet lower than the top of the dam embankment. The <br />approved Pond NHN -001 design done by Arcadis included a 25yr -24hr SEDCAD run assuming no <br />flow through the primary spillway, resulting in a flow depth through the designed 10 ft. wide, 2:1 <br />side slope emergency spillway of 0.18 ft. The resulting freeboard in such a scenario is 1.82 ft. In <br />this worst case situation, where the primary spillway would become blocked, the emergency <br />spillway as built would still have greater than the required 1.0 ft. of freeboard. The emergency <br />spillway channel as -built is a rip- rapped trapezoidal channel, 10ft. wide with 2h:1v or flatter side <br />slopes. <br />6. The SEDCAD run provided for pond NHN -001 is based on one 114.9 acre watershed. <br />The run also includes Muskingum routing information. The SEDCAD User's Manual <br />indicates that this routing function is used when there are multiple subwatersheds and a <br />given subwatershed does not flow directly to the design structure but rather is routed (via <br />ditch, culvert, etc.) to the structure. This does not appear to be the case with the NHN -001 <br />watershed. Please revise the design to omit this routing or break the watershed into the <br />subwatersheds indicated on Map 2.05.3(4) -1 and include appropriate routing for each <br />subwatershed and structure. <br />WFC Response: The four SEDCAD runs included with this submittal were done with Structure <br />Networking Muskingum K & X values equal to zero, and used a single watershed, land flow <br />condition 8 for the 114.9 acres watershed, as was done in the approved permit SEDCAD runs. <br />7. The sedimentology portion of the SEDCAD run provided for pond NHN -001 utilizes a control <br />practice factor (C) of 0.45. The curve number used for the watershed (91) indicates that the area is <br />bare. Therefore, the "C" value should be 0.9. Please revise the design accordingly. <br />WFC Response: The four SEDCAD runs included with this submittal have been revised using a <br />control factor "C" of 0.9. <br />Engineering I Geotechnical <br />The approved design for Pond NHN -001, prepared by Arcadis U.S., Inc., is provided in Appendix <br />2.05.3(4) -1 of the permit. DRMS requirements for pond embankment construction are prescribed in <br />Section 4.05.9 of the Coal Regulations. A List of the applicable sections, with comments, is provided <br />below. [The NHN -001 embankment height is less than 10 feet from the bottom of the channel to the <br />bottom of the spillway, and this pond does not meet the USDA SCS TR60 criteria for a Class B or C <br />impoundment; therefore, many of the requirements of 4.05.9 are not applicable.] <br />3 <br />