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MEMORANDUM Review of Geotechnical Study Proposed Main Street Apartments 353 Main Street, Redwood City, California May 18, 2018 Project No. 1-1089 Page 6 of 7 one -another. These may also incidentally interconnect surface derived water into the groundwater. If not properly mitigated, these issues may result in significant environmental impacts from the Project, and should be studied and analyzed. Liquefactionisettlement mitigation needs supporting documents Reference No. 2 addresses significant magnitudes of static settlement as a result of the proposed building loads and liquefaction due to seismic activity. The report recommends Drilled Displacement Piles (DDP) as a mitigation within the building areas. Proper analyses and study of the DDP method as mitigation should be performed and presented, to include geotechnical review of actual details of the configuration including depths, diameter and reinforcement characteristics. The areas of the Project outside of the building foundation areas do not appear to include Drilled Displacement Piles (DDP) mitigation. The effects of the undocumented fill, bay mud and liquefaction potential in driveway areas and utility corridors should be addressed and quantified so that the result movements are with project design and construction tolerances. • Lateral Spread Reference No. 2 addresses significant lateral spread potential into the adjacent Redwood Creek. This is an identified significant impact to the Project that must be mitigated to a level that is less than significant. Mitigation measures are not specifically identified in the report. It is our professional opinion that mitigation measures have not been adequately addressed and studied relative to the top of slope improvements including retaining walls, driveways, flatwork and other improvements. The potential for lateral movement should be quantified as part of the building Drilled Displacement Piles (DDP) mitigation. • Selche The subject vicinity is located proximal to the San Francisco Bay and sits at very low elevations. It is also situated in an area of high seismic exposure. Given the previously discussed Monte Carlo considerations, a significant earthquake may create Seiche (a sloshing effect of a waterbody in response to earthquake creating flooding) — particularly with regard to proximity to tidal and creek influences. This significant impact must be analyzed and mitigated. CONCLUSIONS 1 CLOSURE In conclusion, the issues identified above should be evaluated in more detail and accordingly resolved as required in accordance with the requirements of CEOA. Further, based on our experience, this project is much more complicated from both an engineering and construction standpoint than represented in items 1 through 6 of the referenced Materials, particularly with regard to groundwater, foundations, inadequate fills and related soils and their mitigation, and seismic issues. 350 Fischer Ave. Front • Costa Mesa, CA 92626 • P: 714 668 5600 • www.G3SoilWorks.com