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• Conclusions <br />It appears that the slope failure that has occurred to the northeast and east of Pond 16 at the <br />Seneca IIW Mine 'is the result of a combination of factors, the most important of which is the <br />presence of a relatively shallow groundwater table at the site that is generally seeping <br />through the fill materials placed at the site, as well as the underlying natural clays and <br />weathered claystone materials. The groundwater appears to have saturated and weakened <br />the fill materials, natural clays and weathered bedrock materials that overlay the more <br />competent claystone bedrock materials. The excavation/removal of the soils from the toe of <br />the natural slope, which were probably marginally stable prior to the construction of Pond <br />16, as well as the placement of the fill materials over the natural soils related to the haul road <br />that was previously located within the slide area further lowered the forces resisting slope <br />movement, thus resulting in the existing failure. <br />Based on the subsurface conditions encountered at the subject site, our understanding of the <br />history of the subject slope failure and development of the features at the site, and the results <br />of this investigation, we believe that there are a several alternatives for <br />stabilizing/reconstructing the subject slope failure. However, the type and degree of slope <br />i reconstruction/remediation will be highly dependent on the amount of site dewatering that <br />will be required. A number of test holes and piezometers have been installed across the <br />failed area, as well as above the failed area to evaluate the direction of the groundwater flow <br />and the potential groundwater sources. <br />Based on the information obtained as of this date, weAtrongly recommend that two test <br />trench/pits be excavated across the slide area so that the additional information regardingrthe <br />depth and condition of the bedrock materials and groundwater flows can be better evaluate4. <br />We also recommend that the, groundwater levels in the piezometers (wells) be monitored for <br />at least 6 months after the trench/pits are excavated The dewatering/underdrain system and ffi <br />site grading- details will be designed after the trench/pits are excavated and the groundwater <br />levels have been monitored for at least 6 months. <br />A discussion of the geologic and geotechnical considerations related to the existing slope <br />failure are outlined herein. <br />• <br />Job Number: 08-8099 NWCC, Inc. Page 1