Geotechnical/Geologic Investigation Addendum <br />Capital Hill PUD <br />Eugene, Oregon <br />Ron Derrick Professional Geotechnical Engineer. Mr. Sandstrom also traversed the Capital PUD <br />site and accessible surrounding areas on foot to map the geologic surface features. Our <br />conclusions are that the proposed site development will not increase the risk of gross land <br />movement in the area. Due to the relatively flat topography (<25%) for most of the area proposed <br />for development, mass movement of earth materials is not expected, the majority of the proposed <br />streets improvements are in areas of existing paved roads or former cleared and graded access <br />ways. The majority of the building pads will also be in areas with less than 25% slopes with the <br />exception of those along the east side of the site where slopes increase to >40%. The ground <br />surface of these lots will not be disturbed as part of site development and will be addressed <br />individually for site specific home designs that are expected to be stepped or pier style foundation <br />systems founded into the competent volcanic rock material to minimize impacts. <br />To assess the impact of the site development on the stability existing slopes in the area of <br />development and the surrounding areas, three main components of slope stability were assessed: <br />1) changes to mass at the base of slopes, 2) changes to mass at the top of slopes, and 3) infiltration <br />of water into the slope soils. The proposed development is on the top of the ridgeline and will not <br />the stabilizing mass at the base of slopes. Site earthwork has been designed to generally conform <br />to the existing ground contours and no additional soil mass will be placed at the top of slopes. <br />The development will capture stormwater runoff from impervious surface areas and convey that <br />water to a suitable point of disposal, thereby potentially reducing the amount of water that could <br />infiltrate into the soil on the slopes. <br />Finally, numerous landslide forms are mapped on both the east and west side of the ridgeline in <br />areas of existing residential development. The primary area proposed for development in the <br />Capital Hill PUD is the only area on this hill that is outside of mapped landslide hazard areas. See <br />attached plan showing the limits of the proposed development, mapped landslide areas, and the <br />surrounding residential development that has been constructed on steeper slopes in mapped <br />landslide areas. <br />Sincerely, <br />Branch Engineering Inc., <br />~6l <br />r PN <br />#16,1OREGON <br />15, <br />J. D <br />EXPIRES: 12131/2017 <br />Ronald J. Derrick, P.E., G.E. <br />Principal Geotechnical Engineer <br />Branch Engineering, Inc. <br />Gary Sandstrom, C.E.G. <br />Certified Engineering Geologist <br />2 <br />