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*:/ : 11-1 h WA <br />site would be covered with landscaping and paved surfaces. The replacement parks would provide rock bio <br />swale and drywell stofmwater capture system to control stormwater. Therefore, erosion impacts would be less <br />than significant. <br />c) Be located on a geologic unit or soil that is unstable, or that would become unstable as a result of <br />the project, and potentially result in on- or off -site landslide, lateral spreading, subsidence, <br />liquefaction, or collapse? <br />Less Than Significant Impact. The replacement park sites atop younger alluvial fan deposits derived from <br />sedimentary rock (USDA 2018). As discussed in Section 3.6a(iv), the proposed project would not result in on - <br />of off site landslides. Lateral spreading refers to lateral displacement of large, surficial blocks of soil as a result <br />of pore pressure buildup or liquefaction in a subsurface layer. As discussed in Section 3.6a(iii), Raitt Street Site <br />may be susceptible to liquefaction, while The 6th Street Site is not in the high liquefaction hazard zone. <br />Natural soils may be susceptible to expansion, consolidation, and collapse (including hydrocollapse with the <br />addition of water). Consolidation is a condition that occurs when increased load is placed on soils with low <br />relative density, causing pore spaces to become smaller and, where saturated, forcing water to be squeezed out. <br />Hydrocollapse is a condition that occurs when a dry soil that can withstand increased load in a dry condition <br />collapses upon saturation. Based on the expected subsurface conditions beneath the site, expansion, <br />consolidation and collapse are not likely to be an issue at the site. Any structures built for this project would <br />adhere to the most recent version of the CBC. Impacts would be less than significant. <br />Subsidence of the ground surface has been reported in the alluvial basins where significant amounts of <br />groundwater (often in an overdraft condition) or petroleum products (oil and natural gas) are withdrawn over <br />several decades. The primary cause of nontectonic subsidence in alluvial basin areas has been the alluvial <br />compaction by closing of porosity due to removal of large quantities of fluid (groundwater of oil). For <br />groundwater basins this results in a significant lowering of the groundwater levels and in oil fields depletion of <br />the oil reserves. The proposed project would not remove significant quantities of water or other fluids from <br />the ground. For these reasons, the potential for subsidence is low. No impacts related to subsidence would <br />occur. <br />d) Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), <br />creating substantial direct or indirect risks to life or property? <br />Less Than Significant Impact. Expansive soils swell when they become wet and shrink when they dry out, <br />resulting in the potential for cracked building foundations and, in some cases, structural distress of the buildings <br />themselves. The replacement park sites may contain expansive soils. However, expansive soils would be <br />excavated and replaced with imported fill materials with acceptable expansion potential, where necessary, as <br />approved by the CBC. The proposed development includes underground utilities, playground equipment, <br />restroom, and shade canopies, and standard grading technologies and compliance with current grading <br />requirements would reduce impacts from expansive soils to a less than significant level. <br />75C-91 <br />