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• <br />Conclusions <br />It appeazs that the slope failure that has occurred to the north and northeast of Pond 12 at <br />the Yoast Mine may be a result of a combination of factors, the most important of which <br />is the presence of a relatively shallow groundwater table at the site, especially during the <br />spring and eazly summer months when the runoff at the site is the greatest. The <br />groundwater/runoff appeazs to have saturated and weakened the natural clays and <br />weathered claystone materials that overlay the more competent claystone-shale bedrock <br />materials. The excavation/removal of the natural soils from the toe of the <br />originaUundisturbed natural slope, which were probably mazginally stable prior to the <br />construction of Pond 12, further lowered the forces resisting slope movement and the <br />placement of the fill materials over the natural soils increased the driving forces, thus <br />resulting in the existing failure. <br />Based on the subsurface conditions encountered at the subject site, our discussions with <br />Jay James of JEC, Inc. regarding the history of the subject slope failure and development <br />of the features at the site, and the results of this investigation, we believe that there aze a <br />• ~ several alternatives for stabilizing/reconstructing the subject slope failure. However, the <br />type and degree of slope reconstruction/remediation will be highly dependent on the <br />amount of site dewatering that will be required. A number of test holes and piezometers <br />were installed across the failed azea; however, these piezometers were installed in late <br />June and early July and after the seasonal runoff had occurred. We strongly recommend <br />that the groundwater levels be monitored until next summer so that the amount and <br />direction of the groundwater flow can be better evaluated and an effective dewatering <br />system can be designed. <br />A discussion of the geologic and geotechnical considerations related to the existing slope <br />failure are outlined herein. <br />Purpose and Scope of Study <br />This report presents the results of a geotechnical evaluation for the slope failure situated to the north and <br />northeast of Pond 12 at the Yoast Mine. The site is more specifically in Section 19, Township 5 North, <br />Range 87 West in Routt County Colorado. The approximate locations of the project site is shown in Figure <br />• #1. <br />Job Number: 07-7600 NWCC, [nc. Page 1 <br />