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CORNERSTONE C. EARTH GROUP seismic events. The procedure involves calculating the yield acceleration, defined as the inertial force necessary to cause the static factor of safety to reach 1.0, from the traditional limit- equilibrium slope stability analysis, for a single critical failure surface. A simplified Newmark analysis was performed with GSTABL7 to estimate a probable maximum displacement. This analysis, in combination with the results of the pseudo-static analysis, is typically used to evaluate the final design-level slope to determine if the estimated movement is acceptable or if mitigation is required. The results of our slope deformation analysis indicate probable maximum displacements on the order of 2 to 4 inches. Based on our analysis and the estimated factors of safety, in our opinion, displacements will be limited during strong ground shaking; however, some displacement is possible within approximately 50 feet of the quarry slope. Based on our review of the proposed development plan and the proposed development setback from the top of the quarry slope ranging from 85 to 90 feet, it is our opinion that the potential impacts to the development due to slope deformation are low. 4.7 FLOODING Flooding may be caused by intensive rainfall, tsunami or seiche, or dam or levee breaks. The terms tsunami and seiche describe ocean tidal waves or similar waves in closed bodies of water. The site is more than 10 miles inland from the San Francisco Bay shoreline. Therefore, the potential for inundation due to tsunami or seiche is considered remote. The site is located adjacent to Lake I of the former Hanson Aggregates Quarry pit. The water surface level in the lake is reportedly to range from Elevation 250 to 330 feet. The proposed high-water level is roughly 30 feet below the current site grades; therefore, the potential for inundation due to a seiche is considered low. As shown on the July 4, 1988 Federal Emergency Management Agency (FEMA) "Flood Insurance Rate Map' (FIRM), this site is within Zone C, described as "Area of minimal flooding". 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 located within a dam failure inundation area for the Del Valle Reservoir. SECTION 5: CONCLUSIONS From a geotechnical viewpoint, the project is feasible provided the concerns listed below are addressed in the project design. Descriptions of each concern with brief outlines of our recommendations follow the listed concerns. Presence of undocumented fill and soil stockpiles Moisture sensitivity of near-surface soils Ponderosa Active Adult Community Page 10 132-2-1