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11. Seneca did not depict a drainage channel at the outlet of the Wadge Impoundment and the PeCOCO [mpoundment. The Wadge Impoundment collects all of the drainage from the northern portion of the Seneca II Mine. Please locate and design a channel diverting water from the Wadge and PeCOCO impoundments to Grassy Creek and Little Grassy Creek. 12. Culvert 2A directs the drainage from SI[PM-15 down a steep slope to the Wadge Impoundment. Seneca proposes leaving this 500-foot long culvert as part of the postmining drainage control system. The Division questions the use of a culvert as a diversion rather than an open channel for the postmining configuration. An open channel would be more appropriate for long term stability and maintenance. Please reevaluate the location and design for an open channel leading to the Wadge Impoundment. 13. Rule 4.05.4 requires that diversions draining a watershed of at least one square mile be designed for the 100-yeaz, 24-hour storm event. The watershed azea is greater than 640 acres where SIIPM-5 ties in with SIIPM-1. Please design the SIIPM-1 postmining channel to pass the flow from a 100-year, 24-hour storm event. 14. On Exhibit 7-19, Seneca located 23 postmining drainage channels. A majority of the channels located on the backfilled azeas have a straight configuration down the reclaimed slope rather than a meandering pattern. Channels with a meandering pattern more closely resemble the premising drainage configuration. Please reevaluate the proposed channel configurations along the backfilled slopes so that they more closely resemble the premising drainage channels. 15. Seneca deigned SIIPM-4 (mid) channel using a grade of 33%. Above the intersection of SIIPM-16, the slope of SIIPM-4 ranges from 44% to 50%. Seneca needs to design this steep section of channel using the actual grade on site. Seneca may want to consider avoiding this steep section by routing the diversion slightly north of the proposed location. The slopes are not as steep and could join SIIPM-16 at the inlet of T-23. Please reevaluate the design, location and cross section of diversion SIIPM-4, and make the appropriate changes. 16. Drainage channel SIIPM-8 and the temporary Wadge Diversion aze combined into one channel. It is difficult to determine where the Wadge Diversion stops and where SIIPM-8 begins. Please indicate on Exhibit 17-9 where the temporary Wadge Diversion stops, and where SIIPM-8 begins. 17. Seneca should include a description of the granular filter layer or geotextile filter fabric to be used in the reconstructed drainage channels prior to placement of the rip-rap material. 18. For each drainage channel, Seneca determined rip-rap size depending on the grade of the diversion. It would be helpful if the rip-rap size transition areas were identified on Exhibit 7-19.