2011-07-01_PERMIT FILE - C1982057A (3)

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n The soils excavated from the trenches were stockpiled along the edges of the trenches. The placement of the excavated materials above the edges of the trenches /pits significantly reduced the depth to which the trenches /pits could be excavated. It should be noted that in our May 2010 site visit, we observed that the northern ends of the trenches /pits had been backfrlled to allow access to the mine and private property to the east and south. It should be noted that a slight to moderate amount of seepage was observed in the east trench and the west trench was dry. NWCC also measured the groundwater levels in the piezometers /monitor wells on September 18, 2009 and May 26, 2010. It should be noted that the piezometers installed in test holes TH -2, TH-4 and TH -6 had been compromised during the construction of the trenches /pits. Therefore, the groundwater measurements could not be obtained from these wells. Groundwater measurements, taken on May 26, 2010 indicate that the groundwater levels on that date were generally 2 to 5 feet higher in elevation than when measured on September 18, 2009. A table summarizing the groundwater levels and dates measured is provided in Appendix A. Pond 016A Landslide - Site Observations and Subsurface Investigations: Based on our observations made in May and June 2010, it appears that the slope failure that was previously observed above the east - southeast edge of Pond 016A and directly downslope (northwest) of TH -11 had increased significantly in vertical and horizontal displacement. On June 23, 2009 the head scarp for the failure was on the order of 1 to 2 feet in height and approximately 50 to 100 feet in length. It is our understanding that Seneca did some minor regrading in this area last fall; however the length, vertical and horizontal displacement of the head scarp had increased substantially since September 2009 and propagated upslope and crosslope (east - northeast) towards the Shrub Plot Landslide. The head scarp, based on our last site visit in July 2010, appeared to range from 5 to 8 feet in height and was approximately 150 to 200 feet in length. We also observed water flowing from the southwestern and northeastern ends of the head scarp at the time of our site visits in 2010. It should be noted that test hole TH -11, which was located approximately 10 feet southeast and upslope of the head scarp, was drilled at the site in June 2009. To further evaluate the subsurface conditions in this failed area, four test pits (Test Pits 16A -1 to 16A -4) were advanced at the site with a rubber tired backhoe on June 17, 2010. In addition, three test holes (TH -12, TH -13 and TH -14) were advanced on July 1, 2010 with a track - mounted drill rig using 4 -inch diameter continuous flight augers. The test pit and hole locations are shown in Figure #I provided in Appendix B. The subsurface conditions encountered in the test pits and test holes were variable and generally consisted of a layer of topsoil fill materials or clay fill materials overlying natural clays, weathered claystone and claystone bedrock to the maximum depth investigated, 25 feet. Graphic logs of the test holes are shown in Figure #2- Apppendix B; whereas, the logs of the test pits are presented in Figure #3- Appendix B. The Legend and Notes associated with the test hole and pit logs are presented in Figure #4- Appendix B. The fill materials encountered beneath the topsoil fill materials consisted of clays with bedrock fragments and topsoil that were slightly sandy to sandy, fine to medium grained, low to moderately plastic, loose to stiff, moist to wet and dark brown to gray in color. Natural clays were encountered beneath the fill materials in all of the test pits excavated in the slide area and in the three test holes (TH -12, TH -13 and TH -14) advanced within the failure area. The natural clays were slightly sandy to sandy, moderately to highly plastic, fine grained, stiff to very stiff, moist to very moist and dark brown to light brown in color. Weathered claystone materials were encountered beneath the natural clays in TH- 0 12, TH -13 and TH -14, Test Pit 16A -1 and Test Pit 16A -4, and below the fill materials in TH -11, which was located Job Number: 09 -8099 NWCC, Inc. Page 2