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Home My WebLink AboutCUP 2022-0010; CARLSBAD DESALINATION PLANT INTAKE AND DISCHARGE MODIFICATION; SECOND ROUND OF THIRD-PARTY GEOTECHNICAL REVIEW CARLSBAD DESALINATION PLANT INTAKE PHASE 2; 2023-05-24 5710 Ruffin Road | San Diego, California 92123 | p. 858.576.1000 | www.ninyoandmoore.com May 24, 2023 Project No. 109343012 Ms. Jessica Nishiura, P.E. Hunsaker & Associates San Diego, Inc. 9707 Waples Street San Diego, California 92121 Subject: Second Round of Third-Party Geotechnical Review Carlsbad Desalination Plant Intake, Phase 2 4600 Carlsbad Boulevard Carlsbad, California Dear Ms. Nishiura: At your request, we have prepared this letter providing our second round of geotechnical review comments for the project that are focused on the referenced revised geotechnical report prepared by HDR Engineering, Inc. (HDR) dated January 30, 2023. Our comments regarding the revised geotechnical report (HDR, 2023) include the following, while considering our initial comments to the original geotechnical report by HDR dated October 21, 2022: Original Comment 1: The Geotechnical Consultant should review the project grading, shoring, and foundation plans and provide any additional geotechnical recommendations, as appropriate, and indicate if the plans have been prepared in accordance with the geotechnical recommendations provided in the referenced geotechnical report. Unresolved. No additional information or plan review letter has been provided to our offices. Original Comment 2: While the signature page of the geotechnical report (HDR, 2022) has been signed and stamped by registered Civil and Geotechnical Engineers, due to the extensive geologic discussion included within the report, consideration should be given to having the report signed by a registered Professional Geologist or a Certified Engineering Geologist as well. Unresolved. No additional information or response has been provided to our offices at this time. Original Comment 3: Addressed in the HDR report dated January 30, 2023. Original Comment 4: Addressed in the HDR report dated January 30, 2023. Original Comment 5: Table 3-5 on Page 10 of the geotechnical report (HDR, 2022) presents moment magnitudes of nearby active faults based on a 975-year return period. The Geotechnical Consultant should provide justification for only utilizing the 975-year return period magnitudes for this table, since the report notes that the Screen Structure and Electrical Building will be based on the 2019 California Building Code (which is based on a seismic event having a return period of 2,475 years). Geotechnical & Environmental Sciences Consultants Ninyo & Moore | 4600 Carlsbad Boulevard, Carlsbad, California | 109343012 | May 24, 2023 2 Unresolved. Table 3-5 of the referenced revised geotechnical report (HDR, 2023) only includes the moment magnitudes of nearby active faults based on a 975-year return period. The Geotechnical Consultant should include the moment magnitudes of nearby active faults based on a 2,475-year return period or justification as to why they are not included. Original Comment 6: Addressed in the HDR report dated January 30, 2023, assuming that the Preliminary Design Report referenced in the report (HDR, 2023) is considered acceptable to the City of Carlsbad. Original Comment 7: Addressed in the HDR report dated January 30, 2023. Original Comment 8: Addressed in the HDR report dated January 30, 2023. Original Comment 9: Addressed in the HDR report dated January 30, 2023. Original Comment 10: Addressed in the HDR report dated January 30, 2023. Original Comment 11: Addressed in the HDR report dated January 30, 2023. Original Comment 12: In several sections of the report, the figure numbers called out in the text do not match the figure numbers presented in the report. The referenced figure numbers within the body of the report should be updated, as appropriate. Specifically, in the referenced revised geotechnical report (HDR, 2023), the Geology Map is labeled as Figure 7 on Page 5 of the report, the Cross Section A-A’ is labeled as Figure 8 on Pages 5 and 7, the Regional Fault Map is labeled as Figure 9 on Page 10, the Liquefaction Susceptibility Map is labeled as Figure 10 on Page 13 and the Tsunami Inundation Map is labeled as Figure 11 on Page 15. New Comment 13: Section 4.1 of the referenced revised geotechnical report (HDR, 2023) indicates that driven piles are no longer being considered for the project and that cast-in-drilled-hole (CIDH) concrete pile foundations are being recommended. Section 4.1.1 and Appendix F of the report provide recommendations for the ultimate pile capacities. The Geotechnical Consultant should provide recommendations for the geotechnically-related factors of safety for the design pile capacities or include the load resistance factors. New Comment 14: The referenced revised geotechnical report (HDR, 2023) indicates that due to the site conditions, the CIDH pile foundations may be installed using steel casing. As noted in Section 5.2 the use of casing can adversely affect the frictional resistance of the CIDH pile foundation. The Geotechnical Consultant should quantify what the CIDH pile capacity would be if the steel casing is left in-place. We appreciate the opportunity to be of service. Respectfully submitted, NINYO & MOORE Jeffrey T. Kent, PE, GE Principal Engineer CTF/JTK/mp Attachment: References Ninyo & Moore | 4600 Carlsbad Boulevard, Carlsbad, California | 109343012 | May 24, 2023 3 REFERENCES American Association of State Highway Officials (AASHTO), 2017 AASHTO LRFD Bridge Design Specifications 8th Edition. American Society of Civil Engineers (ASCE), 2017, Minimum Design Loads for Buildings and Other Structures, ASCE 7-16. California Building Standards Commission, 2019, California Building Code (CBC), Title 24, Part 2, Volumes 1 and 2. California Department of Transportation (Caltrans), 2018, Corrosion Guidelines (Version 3.0), Division of Engineering and Testing Services, Corrosion Technology Branch: dated March. California Department of Transportation (Caltrans), 2020a, Soil Cut Slopes, Caltrans Geotechnical Manual, dated January 2020. California Department of Transportation (Caltrans), 2020b, Liquefaction-Induced Lateral Spreading, Caltrans Geotechnical Manual, dated January 2020. California Department of Transportation (Caltrans), 2021, Corrosion Guidelines (Version 3.2), Division of Engineering and Testing Services, Corrosion Technology Branch: dated May. California Geological Survey, 2008, Guidelines for Evaluating and Mitigating Seismic Hazards in California, Special Publication 117A. HDR, 2022, Geotechnical Design Report, Carlsbad Desalination Plant Intake Phase 2, Poseidon Water, Carlsbad, California, dated October 21. HDR, 2023, Geotechnical Design Report, Carlsbad Desalination Plant Intake Phase 2, Poseidon Water, Carlsbad, California, dated January 30.