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Caribou Industries Proposed Alternative Seismic Improvements - 888 North Main Street July 25, 2018 Page 3 2.2 Geologic Materials According to published geologic reports and maps, the site is underlain by Holocene- to late Pleistocene-age alluvial fan deposits consisting generally of unconsolidated clay, silt and sand (Morton and Miller, 2006; Sprotte et al., 1980). Furthermore, our 1964 report for the site indicates admixtures of silt, clayey silt, sand and gravelly sand extending to the maximum explored depth of 71 feet below ground surface (bgs) (LeRoy Crandall and Associates, 1964). Fill soils were not encountered. Fill soils may be present between boring locations or as a result of subsequent construction or grading. The Quaternary-age alluvial deposits underlying the site are estimated to be about 2,000 feet thick and overlie Tertiary-age sedimentary bedrock (Sprotte et al., 1980). 2.3 Groundwater The site is located in the Coastal Plain of Orange County groundwater basin according to the California Department of Water Resources (DWR, 2003). Water level measurements from the Orange County Water District (OCWD) indicate that the water level in the principal aquifer was at approximately Elevation -35 at the site for June 2015 (OCWD, 2018). This elevation corresponds to a depth of 163 feet at the site. In our 1964 report, groundwater was not encountered in any exploratory boring drilled to the maximum drilled depth of 71 feet bgs (below ground surface). According to the OCWD (2015) and the California Geological Survey [CGS, previously the Division of Mines and Geology (CDMG)] the historic-high groundwater level is 40 feet bgs or deeper (CDMG, 1997). 2.4 Geologic-Seismic Hazards Fault Rupture The site is not within a currently established AIquist-Priolo Earthquake Fault Zone (A-P Zone) for surface fault rupture hazard (CGS, 2018a; CGS, 2002). An A-P Zone is an area which requires investigation to evaluate whether the potential for surface fault rupture is present near an active fault (CGS, 2018b). An active fault is defined as a fault with surface displacement within the last 11,700 years (Holocene). The closest active fault, and established A-P Zone, with the potential for fault surface rupture is the Newport-Inglewood fault zone, located approximately 9 miles southwest of the site (Jennings and Bryant, 2010; USGS-CGS, 2006; CGS, 2002). Faults with the potential for surface rupture are not known to be located directly beneath or projecting toward the site. In our opinion, the potential for surface rupture at the site due to fault plane displacement propagating to the ground surface during the design life of the project is considered low. Although the site could be subjected to strong ground shaking in the event of an earthquake, this hazard is common in Southern California and the effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practices. Liquefaction Liquefaction potential is greatest where the ground-water level is shallow, and submerged loose, fine sands occur within a depth of about 50 feet or less. Liquefaction potential decreases as grain size and clay and gravel content increase. As ground acceleration and shaking duration increase during an earthquake, liquefaction potential increases. According to the CGS, the site is not within an area with a potential for liquefaction (CDMG, 1998). Groundwater was not encountered in any our prior borings to a maximum depth of 71 feet. Additionally, the historic-high groundwater level is documented to be 40 feet bgs or deeper (OCWD, 2015; CDMG, 1997). Therefore, the potential for liquefaction adversely impacting the project site is considered to be low. ...