ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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IMPACT Geology,Soils,and Seismicity—Risks to People and Structures Caused by Strong Seismic Ground 4.7.1 Shaking. The project area is approximately 23 miles from the nearest potentially active fault and is located in CBC Seismic Zone 3. The proposed facilities would be designed to meet or exceed current state engineering and design criteria. Further, although not required by the CBC, the City would design its wastewater treatment facilities to protect against severe seismic events and natural disasters. Therefore, construction of the proposed project would not expose people and structures to seismic-related structural and nonstructural damage and associated hazards. This would be a less-than-significant impact. According to the California Geological Survey's Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada,there are no type"A"or`B"faults located within 20 miles of the project area. The area is classified as being in Seismic Zone 3 in the 1997 edition of the UBC and the 1998 edition of the California Building Standards Code(CBC); for this reason,the level of anticipated seismic ground shaking is lower at the project area than in many areas within the state of California. The nearest potentially active fault is the Great Valley fault system, approximately 23 miles from the project area,which is estimated to have a maximum credible earthquake of 6.7 on the Richter scale. Seismic activity in the nine-county San Francisco Bay Area(San Andreas,Hayward, and Calaveras faults) and the Great Valley Fault System could generate strong ground shaking in the project area. Because of this potential fault activity, ground shaking is a hazard for facilities in the San Joaquin Valley. Intensity of the ground shaking would depend on the magnitude of the earthquake,the distance from the epicenter, and the duration of shaking. The damage sustained and the degree of hazard depends on the seismic hazards of each specific site,the type of structure and its building materials, and construction quality. The project involves the construction of wastewater treatment plant improvements,trunk sewers,pumping stations, and an outfall pipeline. The proposed development would be anticipated to experience at least one major earthquake during the operational lifetime of the project. Although the project area would not likely experience a fault rupture, ground shaking could cause structural damage to buildings,wastewater treatment structures,pipelines, and other permanent improvements proposed as part of the project. The City of Manteca and project engineers would be required to comply with the provisions of the CBC. Seismic design provisions of current building codes generally prescribe minimum lateral forces, applied statically to the structure and combined with the gravity forces of dead-and-live loads. The CBC-prescribed lateral forces generally are substantially smaller than the expected peak forces that would be associated with a major earthquake. Therefore,when built according to CBC standards, structures are anticipated to: ► resist minor earthquakes without damage, ► resist moderate earthquakes without structural damage but with some nonstructural damage, and ► resist major earthquakes without collapse but with some structural as well as nonstructural damage. Conformance to the current building code standards does not constitute any kind of guarantee that significant structural damage would not occur in the event of a maximum magnitude earthquake; however, it is reasonable to expect that a well-designed and well-constructed structure would not collapse or cause loss of life in a major earthquake. At this time,the CBC requirements (based on the probabilistic seismic event) are considered the design minimum. Because of the relatively close presence of the Great Valley fault, it is conceivable that the project area may experience ground shaking more severe than the CBC-specified ground shaking(produced by the more distant Greenville/March Creek fault),but the probability of occurrence is lower. In the event of a moderate to major seismic event along the Great Valley fault, ground shaking could result in lateral forces exceeding the capabilities of structures built to minimum CBC design standards. Given these conditions, if project structures and facilities are not designed or constructed appropriately, a large seismic event could expose WQCF,pumping station,wastewater collection system, and recycled water Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4-7.17 Geology,Soils,and Seismicity