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preparation for excavation and repair of the embankment. He also contacted me on the <br />afternoon of 11/18. The operator was able to pertorm the excavation and reconstruction of the <br />embankment during a period of extremely cold weather, during which frozen conditions precluded <br />runoff from disturbed mine areas into the pond. It appears that no actual environmental damage <br />occurred. <br />Fault <br />It is not entirely clear to me what factors caused the instability. It seems possible that leakage <br />from the buried spillway pipe may have contributed. The pond embankment had been in place <br />since the early 1980's, and was originally certified by P.E. William Anderson in July 1983. There <br />was a large flood event in 2001 that completely filled in the pond and caused some erosion of the <br />embankment, but there had been no indication to my knowledge that the flood compromised the <br />integrity of the embankment. The pond was excavated following the flood, and was certified by <br />P.E. Jim Stover in March 2002, April 2003, and March 2004. <br />I inspected the mine on October 13, 2004, and I did not observe any cracking or slumps on the <br />embankment. I noted in the report that "the sediment pond appeared to be properly maintained <br />and functional" and that "water level in the sediment pond appeared to be approximately 10 <br />inches below the primary spillway invert". Apparently, shortly after that inspection there was <br />significant inflow to the pond, and the primary spillway pipe inlet was submerged for some period <br />of time. The 8" PVC spillway pipe had a gated valve at the outlet, so there would have been <br />water in the buried pipe. At some point in late October, the operator noticed a very small area of <br />settling at the downstream toe of the embankment adjacent to the primary spillway pipe outlet <br />(based on what operator representative Rodney Head described to me). They excavated a <br />trench into the embankment in the immediate area of the settling and for a distance along the <br />buried spillway pipe, but based on what Rodney Head described to me on 11/19, there was no <br />observed seepage through the embankment or indication of piping erosion. I was not aware that <br />small holes had been detected in the spillway pipe until I saw Jim Stover's Oct. 28 pond <br />inspection report. Jim subsequently indicated in his email that the holes had been repaired, and <br />the pipe re-buried after his inspection. <br />It would appear that the small settling feature at the toe of the embankment that the operator <br />observed in late October may have been an indicator of the serious instability that became <br />apparent with the cracking and large scale settling in mid November. <br />