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Veritas Construction, Inc. <br />October 6, 2015 <br />ES-4011 <br />Page 3 <br />Soil Type <br />Saturated Unit <br />Moist Unit <br />Friction <br />Cohesion <br />Weight <br />Weight <br />Angle <br />Intercept <br />(pcf) <br />(pcf) <br />(degrees) <br />(psf) <br />Structural Fill <br />135 <br />125 <br />34 <br />0 <br />Dense Till * <br />135 <br />125 <br />38 <br />200 <br />* The soil strength parameters assumed in the analysis are considered conservative with respect to the <br />underlying dense till deposits. <br />The Slope-W stability analysis provides a theoretical factor -of -safety with respect to stability of <br />the slope (and structure) evaluated. In general, a static factor -of -safety of at least 1.5 and a <br />seismic factor -of -safety of at least 1.2 are considered acceptable. With respect to seismic <br />loading, and based on review of local mapping of peak ground acceleration, a lateral seismic <br />coefficient of 0.25g was used for the seismic stability analysis. Based on the results of the <br />slope stability analysis, the following factors -of -safety for static and seismic stability were <br />calculated: <br />Cross Section <br />A -A' <br />B-B' <br />Static F.S. <br />2.28 <br />2.19 <br />Seismic F.S. <br />1.32 <br />1.30 <br />Based on our analysis, the factors -of -safety exceed 1.5 for static conditions and 1.2 for seismic <br />loading, indicating acceptable overall site stability. The results of the stability analysis and <br />accompanying computer output are provided as an attachment to this letter. <br />While the results of the slope stability analysis indicate an adequate factor -of -safety for deep- <br />seated rotational failure, the potential for relatively shallow debris flow type failures does exist. <br />Although no areas of historic debris flow activity were identified as part of our site investigation <br />and fieldwork, the potential does exist, and is common for most sloped topographic settings. <br />With respect to the existing slope areas of the site that will remain unaltered as part of the <br />proposed development, maintaining the current vegetative cover that currently exists on the <br />slopes will help mitigate the potential for shallow debris flow events. Areas of existing <br />vegetation disturbed as part of the development activities should be permanently stabilized with <br />hydroseed or mulch, and replanted with appropriate species of vegetation. <br />Earth Solutions NW, LLC <br />