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LSA ASSOCIATES. INC. CEQA INITIAL STUDY /MITIGATED NEGATIVE DECLARATION MARCH 1011 PREDA STREET PIPE ERIDOES UPGRADE SAN LEANDRO. CALIFORNIA Regional Seismicity. The entire San Francisco Bay Area is located within the San Andreas Fault Zone (SAFZ), a complex of active faults forming the boundary between the North American and Pacific lithospheric plates. Movement of the plates relative to one another results in the accumulation of strain along the faults, which is released during earthquakes. Numerous moderate to strong historic earthquakes have been generated in northern California by the SAFZ. The level of active seismicity has resulted in classification of the area as seismic risk Zone 4 (the highest risk category) in the California Building Code. The SAFZ includes numerous faults found by the California Geological Survey under the Alquist Priolo Earthquake Fault Zoning Act (A- PEFZA) to be "active" (i.e., to have evidence of fault rupture in the past 11,000 years). Discussion: a) Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: i) Rupture of a known earthquake fault, as delineated on the most recent Alquist - Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault? Refer to Division of Mines and Geology Special Publication 42; ii) Strong seismic ground shaking; iii) Seismic - related ground failure, including liquefaction; iv) Landslides? i) Fault Rupture. Less Than Significant Impact. Surface rupture occurs when the ground surface is broken due to fault movement during an earthquake. The location of surface rupture generally can be assumed to be along an active or potentially active major fault trace. The site is not located within a currently designated Alquist - Priolo Earthquake Fault Zone (APEFZ). The nearest APEFZ is the South Hayward Fault, located approximately two miles east of the project site. No active or potentially active faults have been mapped at the project site; therefore, potential for fault rupture at the site is minimal. ii) Groundshaking. Less Than Significant Impact. Groundshaking is a general term referring to all aspects of motion of the earth's surface resulting from an earthquake. and is normally the major cause of damage in seismic events. The extent of ground shaking is controlled by the magnitude and intensity of the earthquake. distance from the epicenter, and local geologic conditions. The • closest active fault to the project site is the Hayward Fault, located approximately two miles to the east. Other major regional faults that could cause groundshaking at the project site include the Calaveras. San Andreas and Greenville Faults. The purpose of the proposed project is to maintain flow capacity and improve pipe performance during future seismic and/or flood events. The existing sewer pipes and pipe bridges were evaluated for vulnerability to earthquake and flood damage in May of 2005 (Creegan and D'Angelo Consulting Civil and Structural Engineers 2005). Seismic analysis of the existing bridge structure indicated that several truss members at the ends of the trusses would be overloaded during a significant seismic event (bridge loading during a magnitude 7.5 earthquake on the Hayward fault was analyzed); additionally, deflection of the bridges during a magnitude 7.5 earthquake could cause pipe leakage at the bell -and- spigot joints. The proposed project includes a Flex -Tend expansion system to address the expected P: 1EG10801 \CEQA\Preda_FINAL_IS•MND.doc (032811 I) 28