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• NECKPIT SLIDE REMEDIATION PLAN SUMMARY <br />Seneca Coal Company (SCC) originally submitted the Slide Remediation Plan fox the Neckpit slide on <br />June 30, 2006 and subsequently revised the original plan to address issues raised by the Division of <br />Reclamation, Mining and Safety (DBMS). The following remediation plan is a cuhniuation of <br />discussions between SCC and DBMS. <br />BACKGROUND SUMMARY <br />A June 28, 20061etter (attached) from MWH to SCC sturunarized the initial investigations completed to <br />develop the slide remediation plan. One key component of the initial investigations was the slope <br />stability analysis. The stability analysis did not change as a result of the subsequent remediation plan <br />modifications presented in this Attachment 20-B. Consequently, the slope stability results summarized <br />in the June 28, 20061etter remain valid and are included as Appendix A, Slope Stability Analysis. <br />A second component of the initial investigations consisted of SEDGAD4 modeling of surface water <br />runoff and affiliated channel designs. The June 28, 2006 letter also summarizes the results of runoff <br />• modeling for Postmine Channels PM-4, PM-4A, PM-4B and PM-4C. These results have not changed; <br />consequently the summary in the letter regazding postmine channels PM-4, 4A, 4B, and 4C remain <br />valid. To maintain cohesiveness in the permit application package (PAP), the SEDCAD4 <br />demonstrations for these postmine channels have been moved to Attachment 20-1, Postmine Drainage <br />Channel Design. The June 2006 SEDCAD demonstration was recreated fox insertion into Attachment <br />20-1 with correct pagination. <br />DBMS indicated, in their October 17, 2006 comments, that the proposed half-round corrugated pipe <br />design for postmine channel is not allowable by regulation. Consequently SCC has removed the half- <br />round pipe design for permanent postmine channel PM-4D, however the half-round pipe will remain as <br />an interim measure until the designed PM-4D is vegetated. Therefore any reference to the permanent <br />half-round pipe in the June 20061etter is no longer valid. <br />REMEDIATION PLAN <br />SCC will grade, shape and configure the slide area and drainage channel PM-4D (see Figure 1, 2006 <br />• Neckpit Landslide Remediation Plan View). Once the area is configured, a turf reinforcement mat <br />(Enkamat 7020) will be placed and secured/anchored over the entire slide area according to technical <br />TR-55 20-B.1 12/06 <br />