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DNS LANDAU Geo Peer Review Letter 1 . 7.12.2022BLD2022-0439 RECEIVED LALANDAU A S S O C I A T E S July 12, 2022 City of Edmonds 121 5th Avenue North Edmonds, WA 98020 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Attn: Ms. Denise Nelson, Senior Permit Coordinator, City of Edmonds, Building Division Transmitted via email to: Denise. Nelson@edmondswa.gov Re: Geotechnical Peer Review Permit Submittal Package for Angle Residence Building Permit No. BLD2022-0439 Edmonds, Washington Landau Associates Project No. 0074213.020.021 Dear Ms. Nelson: An applicant proposes to construct a single-family residence at 15724 72nd Avenue West in Edmonds, Washington (site). The site is located in the North Edmonds Earth Subsidence and Landslide Hazard Area. At the City of Edmonds' (City) request, Landau Associates, Inc. (Landau) reviewed the applicant's permit submittal package for completeness and summarized its findings in a letter, dated April 29, 2022. Landau also completed a geotechnical peer review of the submittal package in accordance with the scope outlined in Task Order No. 22-02 of the 2022 On -Call Geotechnical Engineering Services Agreement. Landau reviewed geotechnical portions of the following documents for compliance with Chapters 19.10 and 23.80 of the Edmonds Community Development Code (ECDC): • CAST Architecture. 2022. Architectural Plans. April 15. • CAST Architecture. 2022. Site Plan. March 25. • LDC, Inc. 2022. Boundary and Topographic Survey. March 15. • LDC, Inc. 2022. Civil Plans. April 13. • Geotech Consultants, Inc. 2021. Geotechnical Engineering Study. November 24. • MOSS Studio. 2022. Tree Retention and Replacement Plan. ND. • SSF Structural Engineering. 2022. Structural Plans. March 29. In Landau's opinion, the geotechnical design recommendations in Geotech Consultants, Inc.'s (GCI) 2021 study are appropriate for the site and the proposed development, with the following exceptions: • Per Chapter 23.80.050(D) of the ECDC, only critical areas reports prepared in the last 5 years may be incorporated into [current] critical areas reports. As such, the critical areas conclusions in GCI's July 12, 2013 geotechnical engineering report are not eligible for inclusion 155 NE 100th St, Ste 302 • Seattle, WA 98125 • 206.631.8680 • www.landauinc.com Geotechnical Review —Angle Residence Landau Associates in the 2021 study and were not considered by Landau during its geotechnical peer review. Based on Landau's interpretation of Chapter 23.80.050(D) of the ECDC, GO can incorporate information from its 2013 report [into its 2021 study], provided it prepares a geologic hazard assessment report detailing any changed environmental conditions associated with the site. • Because GCI's 2013 geotechnical engineering report was excluded from Landau's review, many of the requirements in Chapters 19.10.030(H), 23.80.050(F)1, and 23.80.050(F)2 of the ECDC were noted as outstanding. Per Chapter 23.80.050(C) of the ECDC, a geologic hazard assessment report should be prepared. The report should include the results of a field investigation; an assessment of the presence of each type of geologic hazard identified in ECDC Chapter 23.80.020; and an evaluation of whether the proposed development will increase the risk of landslides and erosion, on and off site. Because GCI's 2013 geotechnical engineering report was excluded from Landau's review, these requirements have been noted as outstanding. As noted, information from the 2013 report that is still relevant today can be used to prepare the geologic hazard assessment report. GO indicates that the outputs of its slope stability analyses are attached to its 2021 geotechnical engineering study; however, no attachments were included. The geotechnical engineering study should be updated to include the outputs of the slope stability analyses. • Per Chapter 19.10.030(E)4 of the ECDC, to the extent that such information is available, applicants shall submit a topographic map and survey that include the lowest footing or basement slab elevation of existing and proposed structures on the property and on adjacent properties. The topographic map and survey shall also include the proposed finished floor elevations. The finished floor elevation of the proposed garage is shown on the civil plans prepared by LDC, Inc., but the lowest footing elevation of the proposed residence is not included in any of the submittal documents. The submittal documents should be updated to include the lowest footing elevation for all structures. • Per Chapter 19.10.030(F) of the ECDC, the civil plans should include provisions for building pad and foundation drainage, the specific location(s) and height(s) of proposed fill stockpiles, and slope protection features (specifically the proposed "stabilization wall"). The civil plans should be updated to include this information. • Per Chapter 19.10.030(B) of the ECDC, the permit submittal package should include structural calculations with specifications. Structural calculations were provided, but specifications were omitted. The permit submittal package should be updated to include specifications. • Per Chapters 19.10.030(H) and 23.80.050(A) of the ECDC, critical areas reports are to be prepared by a geologist licensed in the state of Washington, and geotechnical engineering reports are to be prepared by an engineer licensed in the state of Washington. Because GCI's 2021 geotechnical engineering study serves as both a critical areas and geotechnical engineering report, it should be stamped by a licensed geologist and a licensed engineer. • Per Chapter 19.10.030(H) of the ECDC, explorations should extend at least 6 feet (ft) below the lowest proposed pile or footing elevation. No explorations were completed in support of the proposed "stabilization wall." Furthermore, test pit explorations completed on this property extended only 6 and 7 ft below ground surface. Therefore, the test pit explorations are adequate only if the footing elevations are less than 1 ft below existing grades at the time of exploration and are not deep enough for the soldier piles associated with the proposed July 12, 2022 Geotechnical Review —Angle Residence Landau Associates "stabilization wall." To comply with the ECDC, explorations should be completed in support of the proposed "stabilization wall," and footing elevations should be provided to verify that previously completed test pits are adequate for design of the proposed development. A portion of the proposed residence will be supported on deep foundations; however, no geotechnical recommendations for deep foundation support were provided in GCI's 2021 geotechnical engineering study. To comply with typical engineering practice in the Puget Sound region, the study should be updated to include recommendations for deep foundation support. This letter has been prepared to facilitate the City of Edmonds' evaluation of permit submittal documents for the proposed single-family residence at 15724 72nd Avenue West in Edmonds, Washington. Landau Associates reviewed geotechnical portions of the documents for compliance with Chapters 19.10 and 23.80 of the Edmonds Community Development Code and for conformance with conventionally accepted geotechnical engineering practices. Review of non-geotechnical documents was completed for the sole purpose of verifying compliance with the recommendations in Geotech Consultants, Inc.'s 2021 geotechnical engineering study. Landau Associates' peer review does not diminish the responsibility of the applicant's geotechnical consultant to serve as the project's Geotechnical Engineer of Record. Furthermore, the applicant's consultants are responsible for preparing a design suitable for the site conditions. If you have questions or comments, please contact Sean Gertz at 206.631.8680 or at sgertz@landauinc.com. LANDAU ASSOCIATES, INC. Sean Gertz, PE Senior Engineer S4'. w Steven R. Wright, PE Principal SMG/SRW/mcs [P:\074\213.020\R\ANGLE RESIDENCE GEOTECHNICAL PEER REVIEW LETTER 7.12.2022.DOCX] July 12, 2022