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REVIEWED BLD2022-0439+Geo_Hazard_Statement_of_Risk_-_Geo+4.6.2022_9.44.43_AM+2785015BLD2022-0439 GEOTECH CONSULTANTS, INC- 2401 ]othAveE Seattle, Washington (425)747-5618-5618 RECEIVED May 03 2022 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Nathan and Callie Angle 5194 South Spencer Street Seattle, Washington 98118 via email: nxangle(cDgmail.com; calliehilpert(ccDgmail.cam April 1, 2022 JN 21303 Subject: Geotechnical Hazard Identification/Declaration and Mitigation Statement of Risk Proposed Single -Family Residence 15724 — 7211 Avenue West Edmonds, Washington 98026 Dear Mr. and Mrs. Angle: Our firm has initially prepared a geotechnical engineering study for the proposed Meadowview Estates short -plat project, of which the proposed residence project is located within, dated October 9, 2013. Subsequently, for this specific project, we prepared an updated report dated November 24, 2021. In addition to this past study and report, because the project site is located within the Earth Subsidence and Landslide Hazard Area of North Edmonds, a declaration letter with a statement of risk is needed by the project geotechnical engineer as required per Edmonds Code (ECDC 23.80). This letter provides this declaration and risk statement. In preparation of this needed letter, we have recently visited the project site and reviewed the plans of the project. The plans we reviewed include: 1) Sheets 1 through 8 (which includes a TESC plan), which were prepared by LDC dated February 15, 2022, 2) Sheets A0.1 through A.16, which were prepared by Cast Architecture dated March 25, 2022, 3) S1.1 through S5.2, and SH1, which were prepared by SSF Structural Engineering dated March 29, 2022 and 4) Sheets L2.0 through 4.1, which was prepared by Kenneth Philp Landscape Architects dated July 6, 2021. In preparation of the 2013 study, we performed a full stability analysis in accordance with the ECDC for the entire short plat that included the steep western slope. But as noted in our 2021 report, this analysis needed to be updated to include the most current IBC (and thus seismic analysis) code. This new analysis determined that, for an overall setback of 65 feet from the very steep slope that borders the western side of the property, a concrete -pile wall with a design height of 15 feet was needed for the western side of the residence. The current project plans indicate that the building setback of about 61 to 65 feet, and that a design height of 17 feet and 15 feet was used for the western foundation wall, respectively; the taller, 17-foot design was needed because the wall was needed just inside the 65-foot setback where a 15-foot design height was determined. In addition to the inclusion of the piled western foundation, also as is recommended in the 2021 report, all loads for the residence will be founded on medium -dense to dense or denser native soil. Because of these reasons, and because the site stormwater will be taken to an existing stormwater system (which lowers the amount of water that reaches the western slope and thus provides some increase to the slope's stability), it is our professional opinion that this proposed development is very suitable from a geotechnical engineering standpoint. Also, the proposed development meets the seven standards noted in both ECDC 23.80.060 and 070 as is noted in the 2021 report. GEOTECH CONSULTANTS, INC. Angle April 1, 2022 JN 21303 Page 2 In accordance with the ECDC, a declaration and statement of risk is needed from the geotechnical engineer for the project. As noted above, it is our opinion that the project is suitable from a geotechnical engineering perspective, and therefore we make the following declaration and statement of risk regarding this project and our review of the plans: • In our opinion, the plans we reviewed for the project conform to the recommendations in our 2013 and 2021 study/reports. The risk of damage to the proposed development, or to adjacent properties, from soil instability will be minimized subject to the conditions set forth in our study, and the proposed development will not increase the potential for soil movement. This includes an evaluation regarding the statistical probability of earth movement within a 25 and 125-year period. Buffer and structural building setback recommendations were included in our study regarding this probability and an analysis of potential deep-seated soil movement. The guidelines of the 2007 Landau Summary Report were included in the analyses, conclusions, and recommendations presented in our 2013 and 2021 study/reports. • That the risk of damage to the proposed development, or to adjacent properties, from soil instability will be minimized subject to the conditions set forth in the report and that the proposed development will not increase the potential for soil movement. The erosion and sediment control plan is very adequate with respect to the site conditions and the findings of the two studies. We trust that this letter meets your immediate needs for the proposed development. Please contact us if we can be of further service. cc: Cast Architecture — Forrest Murphy via email. forrest(a_castarchitecture.com DRW:kg Respectfully submitted, GEOTECH CONSULTANTS, INC. D. Robert Ward, P.E. Principal GEOTECH CONSULTANTS, INC.