2019-040 - Mainplace Mall Transformation

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MainPlace Mall Transformation Project 12126.001 dense to dense silty sand. However, the test boring location map (Plate 1 referenced in the ISE's report) could not be located for review. Eight (8) hollow -stem soil borings (LB-1 through LB-8) were drilled during our feasibility exploration. All borings were located in the existing parking lot areas and no subsurface exploration was performed inside existing building footprint. Locations of the exploration borings and boring logs (LB-1 through LB-8) are presented in Figure 2 and Appendix C, respectively. Artificial fill materials encountered in the borings indicate fill depths ranging from approximately 5 to 10Y2 feet bgs. The fill materials encountered generally consist of brown to dark brown, loose or soft silty sand and clayey sand with trace amounts of construction debris. The fill materials are likely associated with the existing improvements and initial development of the site. Localized thicker accumulations of fill materials should be anticipated elsewhere at the site. However, the records for fill placement were not available for review. Therefore, the existing fill at the site is considered undocumented. 2.2.2 Quaternary Age Young Alluvial Fan Deposits: (Qvf) Quaternary age (Holocene) young alluvial fan deposits generally consisting of brown to dark brown and gray, loose to very dense or soft to stiff sand, clayey sand, silty sand, clay, silt, and gravel with isolated layers of sandy clay were encountered during our recent subsurface exploration at the site beneath the artificial fill materials to the maximum explored depth of 51 Y2 feet bgs. The alluvial soils encountered by others (ISE, 1985a) throughout the site to the maximum depth explored of approximately 51 feet bgs generally consist of silty sand, sand, gravelly sand, sandy silt, silt, clayey silt and clay. The materials are consistent with the alluvial materials encountered in our soil borings. 2.3 Groundwater Groundwater was not encountered during our exploratory borings drilled in the southern portion of the site to the maximum depth of 51 Y2 feet bgs (LB-1 and LB- 2). According to groundwater information obtained through the California Geological Survey (CGS) and presented in the Seismic Hazard Zone Report for the Orange Quadrangle (CGS, 1997), the historically shallowest groundwater depth in the vicinity of the project site is between 30 and 40 feet bgs in the Ito 4 I Leighton