Loading...
GeotechLetterForLot1 Plan Review4-9-20NELSON GEOTECHNICAL ASSOCIATES. INC. April 9, 2020 Mr. Mark McDowell 23521— 75th Avenue West Edmonds, Washington 98026 Via Email: mhmcdowelll@gmail.com 17311-135" Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com Geotechnical Plan Review Letter McDowell Property Short Plat Residential Development Lot 1 23521— 75th Avenue West Edmonds, Washington NGA Job No. 1016817 Dear Mr. McDowell: This letter presents the results of our geotechnical engineering review of the plans for Lot 1 of the proposed short plat residential development project located at 23521 — 751h Avenue West in Edmonds, Washington. INTRODUCTION We previously prepared a report for this property that included recommendations for the proposed short plat residential development dated December 12, 2017. Project plans consist of constructing a new single-family residence within the northwest corner of the property along with associated paved areas and underground utilities. For our use in preparing this letter, we were provided with the following documents: - Architectural Plan Sheets Al through A8 titled "235_ 75th Avenue West Lot 1," dated May 25, 2019, prepared by McDowell Design Build, Inc. - Structural plan set titled "23251 75th Ave W," dated October 18, 2019, prepared by Custom Design Engineering, Inc. Geotechnical Plan Review Letter NGA File No. 1016817 McDowell Property Short Plat Residential Development Lot 1 April 9, 2020 Edmonds, Washington Page 2 PLAN REVIEW AND CONCLUSIONS We have reviewed the geotechnical aspects of the provided plans and found the plans to be in general compliance with our recommendations as presented in our previous geotechnical report prepared for this project. The soil parameters used in the foundation design appear to be consistent with the recommendations provided in our previous report. The proposed structure is also proposed to be setback approximately 29 feet from the top of the mapped steep slope area to the northeast of the proposed development. In our previous report, we recommended that new foundations associated with the existing residence and garage maintain a minimum 15 foot setback from the top of the steep slope areas along with being supported on a deep foundation system. In our opinion the proposed 29 foot structure setback from the top of the steep slope area to the northeast is feasible provided that foundations are supported directly on competent native glacial till soils. Project plans indicate that the new structure will be supported on conventional shallow foundations cast on competent native soils. NGA should be retained during construction to verify foundation subgrades prior to foundation form placement. We understand that all stormwater runoff from the proposed development will be directed to flow into proposed bioretention systems within the site. Footing drains for the proposed structure are to be directed to a gravel -filled drywell within the eastern portion of the property. As recommended in our previous report, all stormwater runoff from the proposed development should be directed into an approved system and not be allowed to flow over the steep slope areas within the site. Temporary erosion control measures such as silt fences along the downhill side of the proposed development are incorporated into the plans. In our opinion, the proposed temporary erosion control measures appear to be feasible. Any disturbed soils remaining after the proposed development should be revegetated in accordance with our previous report. Permanent erosion control measures such as compost amended soils, ground cover, and permanent seeding and planting have also been incorporated into the plans. We also recommend that the steep slopes and associated setback not be disturbed as a part of the overall development It is our opinion that the proposed residence development within Lot 1 of the overall development should not adversely impact or decrease the existing stability of the steep slope areas, neighboring properties, or critical areas; and is in compliance with the City of Edmonds Codes 23.80.060.A.1-4, 23.80.070.A.3.a-c, and 23.80.070.A.4.a, provided all of our recommendations are fully incorporated into the proposed plans and strictly followed during construction. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Plan Review Letter McDowell Property Short Plat Residential Development Lot 1 Edmonds, Washington NGA File No. 1016817 April 9, 2020 Page 3 We recommend that all of our recommendations provided in our previous report and this letter be strictly followed during construction. MINIMUM RISK STATEMENT Provided that the recommendations in this letter and the geotechnical report dated December 12, 2017 are followed during construction, the areas disturbed by construction should remain stable. Therefore, the risk of damage to the proposed development or to adjacent properties from soil instability should be minimal, and the proposed grading and development should not increase the potential for soil movement. 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 McDowell Property Short Plat Residential Development Lot 1 Edmonds, Washington NGA File No. 1016817 April 9, 2020 Page 4 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. o{ Vvas,6 o °e 2883 g"red Geo�o LEE S. BELLAH Lee S. Bellah, LG Project Geologist ti9 M S V OF WA 9 ���w a 35215 w w SGIsT1E, 10NAL 0 Khaled M. Shawish, PE Principal LSB:KMS:dy NELSON GEOTECHNICAL ASSOCIATES, INC.