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Page 3 P-6803 2. 1'he absence of a regional of detailed site geologic map with appropriate scales makes it difficult to interpret and review the provided subsurface data in geologic context. As presented, the location map (Figure 1), boring location map (Figure 2) and aenal view of the project site (Figure 7) are all shown `not to scale'. The absence of a scale makes interpretation of these maps difficult. Of the maps, the aerial view of the project site is closest to a gcolog~ic map of the property. However, Figure 7 lacks a legend, is not to scale, and does not provide any information on the geologic deposits present on the property. Based on our reconnaissance-level review of the available geologic mapping and field reconnaissance, the site is underlain by deeply weathered Pho-Pleistocene deposits of the Livermore Gravel Formation, locally overlain by clay-rich colluvial deposits (e.g. Dibblee, 1980; Majmundar, 1991; fIelley and Graymer, 1997). 3. Our reconnaissance-level mapping of man-made fill on the site suggests that it is more extensive than shown on Figure 7, including minor road fill along the access road. More importantly, our mapping suggests that the existing fill extends entirely beneath the proposed footprint of the Lot 3 residence shown on Figure 7. In addition, our comparison of available vintage topographic maps (1953 USGS 1:24,000 Livermore Quadrangle) with the provided site topographic plan, combined with our field reconnaissance, suggests that the maximum fill thickness is at least 10 feet and may reach up to 12 feet on northwest corner of the property. This estimate is greater than the estimate of up to 8 feet of till provided in Section 3.2 (page 3). "Phis grreater depth is further contirmed by subsurface exploration by Engeo immediately west of the property line on the Hatsushi parcel. 4. Based on our examination of regional landslide hazard mapping by Nilsen et al. (1973) and Majmundar (1991), no mapped landslides are present on the property. In addition, Majmundar (1991) shows the property in the least susceptible area for landsliding. Neither maps are cited in the KE report although both cover the site and provide additional geologic information on site conditions and potential hazards. Our review of historic aerial photographs (1949 black and white, USDA series GS-JL aerial photographs 2-58 and 2-59) and field reconnaissance contirms the apparent absence of active landslides. 5. During our field reconnaissance, we noted that the margin of the till on the northern portion of the property locally has two failures toward the drainage, including an apparent slump. Localized erosion appears to have cut a Swale into the fill near an old abandoned farm structure. Based on our reconnaissance-level mapping, the existing fill prism extends beneath the entire footprint of the proposed Lot 3 residence. 6. "fo evaluate the expansion potential of on-site soils, one Atterberg Limits test was performed by KE and the results indicated the materials were moderately expansive. However, the sample tested may not be representative of the most expansive near-surface materials at the site, particularly because the USGS symbol for the material was "SC" (indicating there was more sand present than clay). Expansion potential results m the geotechnical reports we reviewed for the Hatsushi parcel to the west and the Clara Lane subdivision to the north reported much higher expansion potentials. Due to the high expansion potential m these adjacent areas, the geotechmcal consultants recommended new homes on those properties be supported on either drilled piers or mat-slab foundations. Should highly expansive materials be present on the Vineyard Pass property, the use of footing foundations as recommended by KF, may result in building damage. In addition, any slabs-on-grade placed on highly expansive soils may need a layer of imported, non-expansive materials placed below the slab to yield acceptable performance; no such recommendation exists in the KE report.