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To: Susan Burgmaier, DRMS December 9, 2011 <br />From: Jill Carlson, CGS <br />Subject: Review of TR -76, landslide repairs at Seneca II West, and notes from September 28; <br />2011 site visit <br />I have reviewed Attachment 20 -E, "Summary Report Identifying Unstable Areas within the 11 -W <br />Disturbance Boundary" of technical revision TR 76 (Seneca Coal Company, November 2011). SCC <br />states (page 20-E-1) "This proposed plan is based on a report prepared by Jill Carlson (CGS)." Our <br />Seneca II -W landslide work during this past summer involved three site visits to observe surface <br />conditions and discuss which of the landslides may- impact structures or areas outside permit boundaries <br />or have long -term impacts on final reclamation. <br />Our field observations and field discussions with the mine operator and geotechnical consultant Qulh 6 -7; <br />2011) were oriented toward improving drainage and revegetation, thereby- improving short term stability, <br />However, CGS did not perform any quantitative investigations or analyses and recommends that such <br />work is needed to ensure long-term stability. The technical revision did not include this information, <br />which includes: <br />• Characterization of slope geometiN and failure surface(s) <br />• Quantitative analysis of driving or shearing forces acting on the slide mass due to water and <br />gravity <br />• Quantitative determination of shear strength values (resisting forces due to cohesion and friction) <br />along the failure surface <br />• Analysis of various stabilization strategies to determine what measures; or combination of <br />measures, would be required to achieve the desired long - term factor of safety. <br />Based on the information submitted, I have the following comments: <br />Oil Well Access Road Slump. This slump should be monitored. Additional stabilization measures; <br />possible including a larger buttress /retaining wall, may be needed if additional movement is observed. <br />Pump House Slide. Monitor. <br />Pit Ramp Slide. Remediation plan outlined in TR -76 is consistent with field discussions <br />Pond 016 Slide Area. Work associated with TR -73 is in progress. Observations of high artesian <br />pressures in several of the wells at the base of the PM -2A drainage basin indicate that high pore water <br />pressures in some strata may be contributing to decreased stability. Monitor. <br />Pond 017 /Stock Tank T -25 Area. Remediation plan outlined in TR -76 is consistent with field <br />discussions. <br />Pond 006 Area Slumps. Monitor. <br />