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625 Cypress Avenue Geotechnical Investigation Project No. W1895-88-01 - 11 - April 23, 2024 the ground acceleration and duration of the earthquake must also be of a sufficient level to induce liquefaction. A review of the State of California Seismic Hazard Zone Map for the Tustin Quadrangle indicates that the site is located within an area designated as having a potential for liquefaction. Groundwater was encountered during our site exploration at a depth of 49½ feet below ground surface. The historic high groundwater level in the area is reported to be between 30 and 40 feet beneath the existing ground surface (CDMG 2001). Liquefaction analysis of the soils underlying the site was performed using the 1996 NCEER method of analysis with the updates by Youd et al. (2001). This semi-empirical method is based on a correlation between values of Standard Penetration Test (SPT) resistance and field performance data. To supplement the SPT blow count data, California Modified Sampler blow count data was converted to equivalent SPT blow counts based on a correlation factor of 0.55 (Rogers, 2006). Screening criteria developed by Bray and Sancio (2006) characterize fine-grained soils which are not susceptible to liquefaction as soils with a plasticity index (PI) that is greater than 18 or with a saturated moisture content that is less than 80 percent of the liquid limit. In order to apply the screening criteria, laboratory testing was performed to evaluate the Atterberg Limits and saturated moisture content of select soil samples. Laboratory test results used for the screening criteria are presented as Figure B16. The liquefaction analysis was performed for a Design Earthquake level by using a historic high groundwater table of 35 feet below the ground surface, a magnitude 6.47 earthquake, and a peak horizontal acceleration of 0.434g (⅔PGAM). The enclosed liquefaction analysis, included herein for boring B1, indicates that the alluvial soils below the historic high groundwater level could be susceptible to approximately 0.3 inch of total settlement during Design Earthquake ground motion (see enclosed calculation sheets, Figures 13 and 14). It is our understanding that the intent of the Building Code is to maintain “Life Safety” during Maximum Considered Earthquake level events. Therefore, additional analysis was performed to evaluate the potential for liquefaction during a MCE event. The structural engineer should evaluate the proposed structure for the anticipated MCE liquefaction induced settlements and verify that anticipated deformations would not cause the foundation system to lose the ability to support the gravity loads and/or cause collapse of the structure. The liquefaction analysis was performed for the Maximum Considered Earthquake level by using a historic high groundwater table of 35 feet below the ground surface, a magnitude 7.3 earthquake, and a peak horizontal acceleration of 0.651g (PGAM). The enclosed liquefaction analysis, included herein for