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REVIEWED ENG RESUB3 BLD2023-1125+Geotechnical_Letter+6.3.2024_8.46.35_AM+4295479Group Northwest, Inc. May 20, 2024 Mr. Bryan Navarro Alderwood Landscaping 3055 — 112th Avenue NE, Building B, Suite #102 Bellevue, Washington 98004 Geolechnical Engineers, Geologists & Environmcntal Specialists G-6056 Subject: Acceptance as Geotechnical Engineer of Record and Modified and Supplemental Geotechnical Recommendations, Proposed Landscaping Improvements, 9309 Olympic View Dr., Edmonds, Washington Reference: Geotechnical Engineering Evaluation, Olympic View Drive Landscaping, 9309 Olympic View Drive, Edmonds, Washington (NGA File No. 1443123). Nelson Geotechnical Associates, Inc., July 7, 2023. Dear Mr. Navarro: This letter presents the acceptance of GEO Group Northwest, Inc. to become the geotechnical engineer of record for the subject project, per your request. We have reviewed the above -referenced geotechnical report (referred to hereafter as the NGA report) and the project plans permit set with revisions up to May 8, 2024. Modified and Supplemental Recommendations Based on our review, we are in agreement with the conclusions and recommendations in the NGA report, but with the exceptions discussed below. • We recommend that the proposed subsurface interceptor drain be keyed into competent native soils that underlie the apparent fills, in order to minimize the potential that water in the fills passes below the trench and toward the steep slope. Based on the findings presented in the NGA report, we anticipate that the depth of the fills may range up to approximately 5 feet below existing grade. 13705 Bel -Red Road, Bellevue, Washington 98005 Phone: (425) 649-8757 / E-mail: info@geogroupnw.com May 20, 2024 Mr. Bryan Navarro — Alderwood Landscaping G-6056 Page 2 • We recommend that the subgrade surfaces for the proposed features (boulder walls, water features, patios, steps, etc.) be compacted to a dense condition prior to installation of the features. • We recommend that the water feature be fully lined and sealed with a durable waterproof layer to minimize the potential for water leakage from the feature. • As an alternative to the proposed inclinometer casing installation and annual monitoring, we recommend that the water feature system be fitted with a water loss detection (such as a monitored float in the system holding tank), alarm, and automatic shut-off facility to minimize the potential for leakage or other water loss from the system. In our opinion, this facility would provide quicker detection and control of a release than the proposed inclinometer installation and measuring. The property owners, however, also should monitor the condition of the proposed water feature system, on a periodic basis (including for changes in water usage) as a backup to the system recommended above. Review of Proposed Stormwater Dispersion Facility A revision to the project plans has stormwater drainage for the driveway to the residence being tightlined to a dispersion trench facility in the front yard of the residence. The proposed facility will be located on the opposite side of the residence relative to the steep slope area, and approximately at least 160 feet away from the steep slope area. The distance between the top of the steep slope area and proposed facility is approximately equal to the height of the steep slope. Based on our review of the site conditions and the information provided in the revised project plans, it is our opinion that the proposed dispersion trench facility for the project is acceptable from a geotechnical perspective and will not adversely affect the stability of the site property (including the steep slope area), or adjacent property. Closing We appreciate having the opportunity to provide Alderwood Landscaping with geotechnical engineering services. Please do not hesitate to contact us if you have any questions regarding this letter. GEO Group Northwest, Inc. May 20, 2024 Mr. Bryan Navarro — Alderwood Landscaping Sincerely, GEO Group Northwest, Inc. Keith Johnson, L.E.G. Project Geologist 1/20/2024 William Chang, P.E. Principal Engineer G-6056 Page 3 5/20/2024 GEO Group Northwest, Inc.