15 ATTACHMENT 9 - Laserfiche WebLink

Page 2 1696-16 PROPOSED CONSTRUCTION The Site Development Plan by Ruggeri, Jensen, Azar and Associates indicates the 20.2-acre site will be subdivided to create 6 typical residential lots, an estate lot with a large house at the crest of the ridge, and a smaller residential hillside lot downhill of the estate property. Moderate grading operations are proposed to create the new home lots, a new cul-de-sac street and a long private driveway to serve the two hillside lots. The grading will consist of cuts and fills up to 15 feet thick for the lower 6 lots, and a large excavation of the hillcrest to create the estate lot. A large cut slope about 40 feet high will be created along the southern property line to lower grades for the relatively flat building pad for the estate home. A 30-foot high cut slope will be graded along the southwestern edge of the lower lots while many of these lots will have 5- to 10-foot high fill slopes created. It is estimated about 52,000 cubic yards of cut will result and about 26,000 cubic yards of the excavated materials will be used as fill; the remaining materials will be off-hauled. SITE CONDITIONS The site conditions as described by the Ten asearch report, generally consist primarily of north-facing slopes of a small mountain ridge feature. In addition, smaller west-facing slopes are present in the southwest corner of the parcel. Many of the slopes have Swale features. Elevations range from about 450 feet along Vineyard Avenue to approximately 670 feet at the top of the hill where the estate lot will be created. Terrasearch indicates the site is underlain by a geologic unit known as Livermore Gravels, based on the published map by Majmundar (1991). They note this map indicates the presence of a large, questionable landslide feature along the northeast property. However, Terrasearch indicates the presence of this feature was not confirmed by their site reconnaissance and review of two sets of aerial photographs. They noted their study identified a number of small dormant landslides and areas of colluvium on the site; the locations of these features were shown on their Site Plan, Figure 2. Terrasearch concluded no active faults passed through the site, but noted the proximity of the site to the numerous active faults in the Bay Area. Table 1, Earthquake Fault Zone Data, presents their summary of this fault information. EVALUATION AND CONCLUSIONS It is our opinion that the geotechnical investigation performed by Terrasearch for this parcel generally conforms to accepted geotechnical standards of practice and the Vineyard Avenue Corridor Specific Plan. However, a number of omissions exist which we believe will require the submittal of a supplemental letter. These items are discussed individually below. Existing landslide evaluation -Based on our examination of regional mapping by Majmundar (1991), the geologic mapping shown is derived in part from original mapping by Nilsen et al. (1975) and Dibblee (1980). Neither maps are cited in the report although both cover the site and provide additional geologic information on site conditions. More importantly, Nilsen shows a large landslide on the southeastern margin of the site. This landslide is larger than the questionable landslide, identified by Majmundar, discussed in the report. This landslide is also shown on the Vineyard Avenue Corridor Specific Plan geologic map. In addition, Nilsen also indicates the presence of another, smaller landslide in the southwest corner of the property. ~1_,4ti K;~~P~ .x ,.a E~i r~ui-fAI ~h~-'. ENC.