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REVIEWED RESUB1 BLD2023-0692+addtl Geotechnical_Report+2.23.2024_11.22.59_AM+4078773NELSON GEOTECHNICAL ASSOCIATES. INC. February 23, 2024 Mr. BK Chen VIA Email: bkchen@gmail.com RESUB Feb 23 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Geotechnical Plan Review Letter Chen 210th Street SW Residential Development 7103 — 210th Street SW Edmonds, Washington NGA Project No. 1209720 17311-135th Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com BLD2023-0692 REVIEWED BY CITY OF EDMONDS BUILDING DEPARTMENT' Dear Mr. Chen: This letter presents the results of our geotechnical engineering review of the civil plans for the proposed Chen 210th Street SW Residential Development project located at 7103 — 210th Street SW in Edmonds, Washington. INTRODUCTION We understand that the proposed development for the property will include the construction of six new townhome residence structures within the eastern portion of the property along with associated paved parking areas and underground utilities. We previously prepared a stormwater infiltration evaluation for the site dated November 12, 2020. In general, we concluded that stormwater infiltration for the planned site development was feasible from a geotechnical standpoint. We understand that the City of Edmonds has requested our review of the civil plans to confirm they are consistent with our previous recommendations in a letter dated August 21, 2023. For our use in preparing this plan review letter, we have been provided with the following documents: • Civil plan set titled "HC Townhouse," dated February 9, 2024, prepared by Home Tech. We have been requested to provide our plan review of the provided civil plans. In the following sections, we summarize the results of our geotechnical plan review. Geotechnical Plan Review Letter Chen 210th Street SW Residential Development Edmonds, Washington NGA File No. 1209720 February 23, 2024 Page 2 PLAN REVIEW We have reviewed the geotechnical aspects of the provided civil plans and found the plans to be in general compliance with our recommendations as presented in our previous geotechnical report. In our previous report, we determined that traditional stormwater infiltration systems founded within the granular native advance outwash soils at depth were feasible within this site. We understand that stormwater within the site will be directed to flow through a series of catch basins into a gravel -filled infiltration trench system within the southern portion of the property. The trench will be 36-feet long, 5-feet wide and 4-feet deep. Based on review of the drainage report, it appears that the infiltration system was sized and designed based on the long-term design infiltration rate provided in our previous report. We recommend that the system be fully founded within the native granular advance outwash soils at depth, and NGA be retained during construction to confirm the soil conditions prior to backfilling the systems. All other recommendations provided in our previous report should be strictly followed. CLOSURE We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Plan Review Letter Chen 210th Street SW Residential Development Edmonds, Washington NGA File No. 1209720 February 23, 2024 Page 3 We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this letter or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Senior Geologist 2.23.2024 Khaled M. Shawish, PE Principal LSB:KMS:dy NELSON GEOTECHNICAL ASSOCIATES, INC.