Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 11 4.7 FLOODING Based on our internet search of the Federal Emergency Management Agency (FEMA) flood map public database, the site is located within Zone X, determined to be outside the 0.2 percent annual chance floodplain. We recommend the project civil engineer be retained to confirm this information and verify the base flood elevation, if appropriate. The Association of Bay Area Governments has compiled a database of Dam Failure Inundation Hazard Maps (ABAG, 1995). The generalized hazard maps were prepared by dam owners as required by the State Office of Emergency Services; they are intended for planning purposes only. Based on our review of these maps, the site is not located within a dam failure inundation area. SECTION 5: CONCLUSIONS 5.1 SUMMARY From a geotechnical and geologic viewpoint, the project is feasible provided the concerns listed below are addressed in the project design. The preliminary recommendations that follow are intended for conceptual planning and preliminary design. A design-level geotechnical investigation should be performed once site development plans are prepared indicating where proposed structures, retaining walls and cut slopes are planned. The design-level investigation findings will be used to confirm the preliminary recommendations and develop detailed recommendations for design and construction. Descriptions of each geotechnical concern with brief outlines of our preliminary recommendations follow the listed concerns.  Differential settlement of proposed fills and cut/fill transitions  Possible excavation difficulties in hard bedrock.  The presence of moderately to highly expansive soils that mantle the hillsides  Localized liquefaction potential near the existing creek 5.1.1 Differential Fill Settlement The conceptual site plan indicates that fills up to about 30 feet thick are proposed on the southern edge of the development area. Foundations constructed over deep fills will be subject to long-term settlement. Even well-compacted fills may experience minor long-term settlements due to secondary strains or hydro-compression. Provided that the fills are placed and compacted in accordance with our recommendations, on a preliminary basis, we estimate that total long-term post-construction fill settlement would be less than approximately ½ percent of the fill thickness. In addition, shallow foundations, such as reinforced or post-tensioned mats, constructed over cut/fill transitions may experience differential movements under static and seismic loading conditions. Therefore, to reduce the potential for differential movement beneath structures on these lots, we recommend that building pads on cut/fill transition lots be over-excavated to provide a more uniform cushion for shallow foundation support. In addition, lots with significant differential fill thickness should he over-excavated to provide a resulting differential fill thickness Ii! CORNERSTONE EARTH GROUP