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353 Main Street Apartments Redwood City, California May 1, 20L8 (Original Report Doted November L8,2076) Foundations The structure may be supported on a deep foundation system consisting of drilled displacement piles (DDP) connected with a structural floor slab. Corrosion One sample of the near surface soilwas collected for corrosion analysis. The sample was sent to Cerco Analytical and tested in accordance with ASTM Test Methods. They conclude that the soil is classified as corrosiveto buried metallic utility pipes. The sulfate concentration of the sample was 38 mg/kg and Type ll or V cement can be used for the foundations and slab-on-grade concrete constructed near surface. Earth Systems does not practice corrosion engineering and we recommend that a qualified corrosion engineer be consulted regarding mitigation of the corrosion effects of the site soils on metals. The results of the test along with a brief corrosivity analysis by CERCO are included at the end of this report, in Appendix D. Groundwater Groundwater was encountered during the subsurface exploration at approximately 18 to 18.5 feet below the surface. The groundwater then rose to 13 feet following drilling operations (please note that boreholes were not left open long enough to allow groundwater levels to stabilize). According to the Palo Alto 7.5 Minute Quadrangle Seismic Hazard Zone Report, historical ground water is less than 10 feet below the existing ground surface. ln general, variations in rainfall, temperature, and other factors may affect water levels, and therefore groundwater levels should not be considered constant. Since ground improvement may come in contact with the groundwater level, the contractor should perform their own study to evaluate the possible need for dewatering measures during ground improvement construction. Seismicity The San Francisco Bay area is recognized by geologists and seismologists as one of the most seismically active regions in the United States. The significant earthquakes in this area are generally associated with crustal movement along well-defined, active fault zones which regionally trend in a northwesterly direction. Although research on earthquake prediction has greatly increased in recent years, seismologists cannot predict when and where an earthquake will occur. Nevertheless, on the basis of current technology, it is reasonable to assume that the proposed development will be subjected to at least one moderate to severe earthquake during its lifetime. During such an earthquake, the danger from fault offset on the site is low, but strong shaking of the site is likely to occur and, therefore, the project should be designed in accordance with the seismic design provisions of the latest California Building Code. lt should be understood that the California Building Code seismic design parameters are not intended to prevent structural damage during an earthquake, but to reduce damage and minimize loss of life. 301842-001 15 1610-038.SER.REV2 7.B. - Page 73