RES 99074 - Laserfiche WebLink

SIGNIFICANT EFFECT Impact 4.2-2: ~10i~,Ans/al~li~. Construction of buildings or site improvements within or adjacent to landslides or slopes prone to landsliding could result in damage during new or continued slope movement. This impact would be considered potentially significant. Changes or alterations have been required in, or incorporated into, the project which mitigate or avoid the significant effects on the environment. Facts in Support of Findin~ The City of Pleasanton has adopted the following measures which will reduce potential slope instability impacts to a less-than-significant level: SIo,uLInS/ahili~. For areas with slopes steeper than 20% or within or adjacent to existing landslides, a slope stability analysis report (addressing static and pseudo-static conditions) shall be prepared by a licensed Civil Engineer and include the appropriate recommendations from the approved geotechnical report for any proposed residential development or roadway construction. The report shall provide recommendations for control of surface drainage, adequate groundwater drainage, and slide mass removal or stabilization, if necessary. The analysis shall bc supported by investigation of site-specific conditions that shall include, but not be limited to: estimated recency of slope failures and potential for continued movement; depth of landslides or colluvial deposits and characterization of slide plane(s); .- shear strength data for subsurface materials at the project site; location of springs; groundwater level data that characterizes seasonal fluctuations; and · justification of seismic coefficient used in pseudo-static analysis. Proposed cut and fill slope designs shall have factors of safety not lower than 1.5 under static conditions and 1.0 under seismic shaking conditions. Prior to the final design of the relocated Vineyard Avenue, the stability of the slopes of the south bank of Arroyo del Valle generally within 200 feet of the proposed location of the roadway shall be evaluated by a qualified geotechnical engineer to determine if slope failures could affect the short- and long-term integrity of the constructed roadway or if construction or operation of the roadway could affect the stability of the banks. A geotechnical report shall be prepared for the City that specifies appropriate slope design and construction. Recommendations within the report shall be implemented in the roadway specifications. SIGNIFICANT EFFECT Impact 4.2-3: Unstable Deep Fffis. The proposed construction of deep fills at the project site could result in the development of adverse soil conditions that could cause deformation of the fills. This deformation could affect the performance of foundations and other site improvements, including roadways and utility lines. This impact would be considered potentially significant. Vineyard Avenue Corridor Spedtic Plan Draft EIR -9- Findings