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BLACK AVENUE RESIDENTIAL DEVELOPMENT 648-26-1 Page 4 encountered stiff to very hard clays interbedded with minor sand layers to a depth of 23 feet. The upper clays were followed by medium dense to dense sands and gravelly sands to about 29 feet, stiff clay to 36 feet, and dense sands to practical refusal of approximately 37 feet. For CPT-4 and CPT-5, stiff clays were encountered to 35 to 37 feet underlain by dense sands to practical refusal depth of 37 and 40 feet, respectively. 3.3.1 Plasticity/Expansion Potential We performed one Plasticity Index (PI) test on a representative sample. The test result was used to evaluate expansion potential of surficial soils. The result of the surficial PI test indicated a PI of 9, indicating low plasticity and expansion potential to wetting and drying cycles. 3.3 GROUNDWATER Groundwater was not encountered in our explorations. Based on our previous experience in the area and review of historic high groundwater maps (CGS, 2008), we anticipate that the high groundwater will be on the order of 30 feet below current grades. Based on the above, we recommend a design groundwater depth of 30 feet. Fluctuations in groundwater levels occur due to many factors including seasonal fluctuation, underground drainage patterns, regional fluctuations, and other factors. SECTION 4: GEOLOGIC HAZARDS 4.1 FAULT SURFACE RUPTURE As discussed above several significant faults are located within 25 kilometers of the site. The site is not located within a State-designated Alquist Priolo Earthquake Fault Zone. As shown in Figure 3, no known surface expression of fault traces is thought to cross the site; therefore, fault surface rupture hazard is not a significant geologic hazard at the site. 4.2 ESTIMATED GROUND SHAKING Moderate to severe (design-level) earthquakes can cause strong ground shaking, which is the case for most sites within the Bay Area. A peak ground acceleration (PGA) was estimated for analysis using a value equal to FPGA*PGA, as allowed in the 2019 edition of the California Building Code when an exception has been taken per ASCE 7-16, Section 11.4.8. For our liquefaction analysis we used a PGAM of 0.82g. 4.3 LIQUEFACTION POTENTIAL The site is within a State-designated Liquefaction Hazard Zone (CGS, Livermore Quadrangle, 2009). Our field and laboratory programs addressed this issue by testing potentially liquefiable layers to depths of up to 43 feet, evaluating CPT data, and performing various tests to further classify soil properties. . Based on our previous experience in the . Based on our previous experience in the CGS,CGS,2008), 2008), we anticipate that the high we anticipate that the high feet below current grades. feet below current grades. Based on the above, we recommend a design groundwater depth of Based on the above, we recommend a design groundwater depth of 30 groundwater levels occur due to many factors including seasonal fluctuation, underground groundwater levels occur due to many factors including seasonal fluctuation, underground drainage patterns, regional fluctuations, and other factors.drainage patterns, regional fluctuations, and other factors. SECTION 4: GEOLOGIC HAZARDS FAULT SURFACE RUPTUREFAULT SURFACE RUPTURE As discussed above several significant faults are located within 25 kilometers of the site. The As discussed above several significant faults are located within 25 kilometers of the site. The site is not located within a Statesite is not located within a State-designated Alquist Priolo Earthquake Fault Zonedesignated Alquist Priolo Earthquake Fault Zone no known surface expression of fault traces is thought to cross the site; therefore, fault no known surface expression of fault traces is thought to cross the site; therefore, fault surface rupture hazard is not a significant geologic hazard at the site.surface rupture hazard is not a significant geologic hazard at the site. ESTIMATED GROUND SHAKINGESTIMATED GROUND SHAKING level) earthquakes can cause strong ground shaking, which is the level) earthquakes can cause strong ground shaking, which is the