2004-05-03_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project April 29, 2004 2003 Annual Reclamation Report Page 5 The displacements indicated at two monitoring points, P-07 and MP-63, are questionable, based on observations at surrounding monitoring points. The monitoring point P-07 is located on the South Wall of the North Pit. The displacement indicated at P-07 for the 2003 yearly interval is 0.40 ft. Surrounding monitoring points within about 100 ft of P-07 indicate approximately an order of magnitude less displacement. The surrounding monitoring points generally indicate a dip direction of about 300°, while the dip direction at P-07 is 349°. These discrepancies are likely due to survey error. A less likely explanation is that displacement at P-07 is the result of very localized slope movement. Monitoring point P-07 is included on Figure A, pending the results of ground-truthing, which will be conducted in early summer 2004. Monitoring point MP-63 is located on the East Wall of the South Pit. The displacement indicated at MP-63 for the 2003 yearly interval is 0.24 ft. Significant displacement has not been observed in this area since the 1996 re-grade. Other monitoring points on the East Wall of the North Pit, indicate approximately an order of magnitude less displacement than MP-63. This discrepancy is likely the result of survey error, but may be attributable to localized slope displacement. Monitoring point MP-63 is included on Figure A, with this area to be ground truthed in early summer 2004. All of the total displacement values for 2003 are less than or equal to 0.24 ft/year, with the exception of P-07 as noted above. The lack of measurable slope displacement data, at a number of monitoring points, suggests that the North Pit slopes have stabilized to less than 0.5 ft/year. As was noted last year, as the number of monitoring points that exhibit slope displacement decrease with time, the remaining points tend to cluster in the northeast corner of the North Pit, and at the south wall of the North Pit. The northeast corner of the North Pit is the location where the two rapid, large-scale slope displacements took place in 1983. The south wall of the North Pit has historically been the second most active part of the North Pit, with the northeast corner being the most active. The south wall of the North Pit also had a rapid, large- scale slope displacement event in 1983. The clustering of slope movement in these two areas, and the lack of slope displacement anywhere else in the North Pit, suggests that the North Pit slopes are becoming more stable. The increased degree of stability is likely related to the pit regrading work done in 1996, and decreased groundwater levels in response to several years of relative) I~ow precipitation at the site It is possible that in future years with above average precipitation, some increase in displacement may occur due to saturation of the slopes. however, it is anticipated that any increase in displacement would be in the range of 0.5 ft. per year. Overall, the potential for catastrophic failure remains extremely low.