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City of Santa Ana Addendum to the <br />MainPlace Mall Transformation Proiect Fashion Square Commercial Center Final EIR <br />Project would result in a less than significant impact related to strong seismic ground <br />shaking. No new impact would occur. <br />Seismic -related Ground Failures and Liquefaction <br />Regarding potential liquefaction, the Main Place Project's seismic hazards review study <br />describes that the southernmost portion of the Project site is potentially susceptible to <br />liquefaction, which could also result in lateral spreading since the site is slightly sloped <br />(Geo 2019). This area generally coincides with an area with historically shallow <br />groundwater between 30 and 40 feet below the ground surface (GEO 2019). In addition, <br />layers of loose to moderately dense sandy soil that are susceptible to seismically - <br />induced settlement exist in the subsurface across the site. Therefore, there is a potential <br />for effects of localized seismically -induced settlement of structures and other <br />improvements on the site (GEO 2019). However, as described previously, the CBC as <br />implemented by the City's Municipal Code provides a minimum standard for building <br />design and construction, and consistency with this standard would reduce the potential <br />of seismic impacts including liquefaction, lateral spreading, and seismically induced <br />settlement to a less than significant level. No new impact would occur. <br />Expansive Soils <br />Expansive soils contain significant amounts of clay particles that swell considerably <br />when wetted and shrink with the loss of water. Foundations and structures constructed <br />on these soils can be subject to uplifting forces caused by swelling, which could <br />potentially result in the heaving and cracking of both building foundations and slabs -on - <br />grade. The seismic hazards review study conducted expansion index testing of onsite <br />soils, which identified that the near -surface site soils exhibit low expansion potential. <br />However, clayey soils exist at the site that could be expansive when subject to change <br />in moisture. The seismic hazards review study determined that implementation of <br />standard engineering and earthwork construction practices, such as proper foundation <br />design and proper moisture conditioning of earthen fills, would reduce the impacts <br />associated with expansive soils to tolerable levels (GEO 2019). Because the Project <br />would be required to comply with the CBC as included in Municipal Code Chapter 8, <br />Article 2, Division 1 through the City's construction permitting process, impacts related <br />to expansive soils would also be reduced to a less than significant level. No new impact <br />would occur. <br />Subsidence <br />Regional ground subsidence generally occurs due to rapid and intensive removal of <br />subterranean fluids, typically water or oil. It is generally attributed to the consolidation of <br />sediments as the fluid in the sediment is removed. The total load of the soils in partially <br />or fully saturated deposits is born by their granular structure and the fluid. When the <br />fluid is removed, the load is born by the sediment alone and it settles. <br />No reports on regional subsidence due to fluid removal have documented subsidence in <br />the site vicinity, and the Project would not involve the removal of water or oil at the site, <br />making the potential for ground subsidence related to fluid removal is not a geologic <br />54 <br />