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WM1h coal elw%sc <br />o <br />mppany Seneca Coal Company <br /> ? ED <br />August 3, 2010 <br /> 5 <br />puc o 200 <br />Mr. Daniel Mathews <br />n, <br />? <br />Division of Reclamation Mining and Safety a'd <br />" <br />, <br />101 South P, Suite 301 <br />Grand Junction, CO 81501 <br />(970) 242-5025 <br />RE: Seneca II-W Mine (Permit C-1982-057) <br />Technical Revision (TR-73), Pond 016 Area Slide Remediation Plan <br />Mr. Mathews, <br />Seneca Coal Company (SCC) is submitting this Technical Revision (TR-73) to present proposed <br />remediation plans for stabilizing the Pond 016 area. The unstable areas around Pond 016/016A have been <br />observed, studied and monitored since early 2008. The attached remediation plan has been prepared <br />using the recommendations from NWCC, who conducted the geotechnical analysis and evaluation. The <br />plan consists of- <br />• Removing portions of permanent roads J/K <br />• Stabilizing Pond 016 slide <br />• Stabilizing the Shrub Plot slump <br />• Removing and backfilling Pond 016A, and <br />• Relocating permanent channel PM-2. <br />In order to justify removing Sediment Pond 016A, SEDCAD 4 analysis was conducted to verify that Pond <br />016 has sufficient existing capacity to retain/handle runoff from futurel Oyr/24hr storm events. SCC took <br />a conservative approach when developing the networking for the SEDCAD analysis to determine the <br />future capacity requirements for Pond 016. <br />1. Six (6) structures/watersheds were assumed (3 null structures, 2 stock ponds and Pond 016), <br />2. No credit taken for routing between structures, <br />3. No credit taken for the six (6) runoff control structures existing within the sub-watersheds, and <br />4. Curve numbers were area weighted using the approved values for land type and hydrologic soil <br />groups. <br />Seneca Coal Company . P.O. Box 670 • Hayden, Colorado 81639 <br />Telephone (970) 276-5217 • FAX (970) 276-5222