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Based on the presence of undocumented fill and variable strength alluvial soils throughout the site, it is expected that some isolated areas of additional overexcavation may be required to remove zones of lower strength, unsuitable soils. As noted previously, portions of the subject site are underlain by medium expansive soils. Support of new fiatwork on medium expansive soils carries additional risk with respect to flatwork movement and potential distress. This report provides recommendations for moisture conditioning and additional steel in the flatwork in order to minimize the potential effects of the expansive soils. However, if additional protection against cracking is desired, the client should consider the placement of a 1 to 2 foot thick layer of non-expansive soil beneath all flatwork. Treatment of Existing Soils: Parking Areas Based on economic considerations, overexcavation of the existing fill soils in the new parking areas is not considered warranted, with the exception of areas where lower strength, or unstable, soils are identified by the geotechnical engineer during grading. Subgrade preparation in the new parking areas should initially consist of removal of all soils disturbed during stripping and demolition operations. The geotechnical engineer should then evaluate the subgrade to identify any areas of additional unsuitable soils. The subgrade soils should then be scarified to a depth of 123: inches, moisture conditioned to 2 to 4 percent above optimum moisture content, and recompacted to at least 90 percent of the ASTM D-1557 maximum dry density. The grading recommendations presented above for the proposed parking and drive areas assume that the owner and/or developer can tolerate minor amounts of settlement within the proposed parking areas. The grading recommendations presented above do not completely mitigate the extent of existing undocumented fill soils in the parking areas. As such, settlement and associated pavement distress could occur. Typically, repair of such distressed areas involves significantly lower costs than completely mitigating these soils at the time of construction. If the owner cannot tolerate the risk of such settlements, the parking and drive areas should be overexcavated to a depth of 2 feet below proposed pavement subgrade elevation, with the resulting soils replaced as compacted structural fill. Treatment of Existing Soils: Retaining Walls and Site Walls The existing soils within the areas of any proposed retaining walls should be overexcavated to a depth of 2 feet below foundation bearing grade and replaced as compacted structural fill, as discussed above for the proposed building pad. Any existing undocumented fill soils should also be removed in their entirety. The foundation subgrade soils within the areas of any proposed non-retaining site walls should be overexcavated to a depth of 1 foot below proposed foundation bearing grade. For both types of walls, the overexcavation subgrade soils should be evaluated by the geotechnical engineer prior to scarifying, moisture conditioning and recompacting the upper 12 inches of exposed subgrade soils. The previously excavated soils may then be replaced as compacted structural fill. t. _SOUT-HIRA G&M Convenience Store #72 - Santa Ana, CA CALIFORNIA Project No. 16G123-1R GEOTECHNICAL Page 17