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Report /14 2.01q-003610 I*($44 5 Q 76ive" GeoPacdic Engineering.Inc. Real-World Geotechnical Solutions Investigation • Design • Construction Support February 25, 2020 GeoPacific Project No. 15-4010 Riverside Homes, LLC 17933 NW Evergreen Parkway, Suite 370 Beaverton, OR 97006 Via email to Wes Boisvert (wboisvert_agriversidehomecom) Subject: GEOTECHNICAL OBSERVATION OF FOUNDATION SUBGRADE ELDERBERRY RIDGE SUBDIVISION—LOT 20 14844 SW 76T"AVENUE TIGARD, OREGON GeoPacific Engineering, Inc. (GeoPacific) conducted on-call density testing and construction observation services for the Elderberry Ridge Subdivision site. This letter addresses the footing subgrade conditions for Lot 20. It is our understanding that the planned structure will consist of a single-family residence utilizing conventional spread footings. GeoPacific personnel visited the site February 251h 2020 to observe the subgrade soils during the foundation excavation for Lot 20. The excavation depths were approximately 12-18 inches below the surrounding grade. The foundation bearing soils consisted primarily of thin compacted fill and stiff, native silt soils, which were evaluated with a hand probe. Probing efforts throughout the native silt soils indicated stiff to dense consistency. The footing layout of Lot 20 is relatively flat with a slope descending about 25 feet elevation at least 30 feet from the home. Footing-to-slope and footing-to-wall setbacks do not appear to be adequate. Based on observed conditions, the footing subgrade soils are considered suitable for foundation support. The foundation subgrade as prepared is considered suitable to support the planned allowable bearing pressure of 1,500 psf. Estimated settlement under the allowable bearing pressure is 1 inch total, and %-inch differential, measured over a horizontal distance of 20 feet. Care should be taken to avoid saturation or disturbance of footing subgrade soils during and after excavation. If footing bearing soils become saturated or disturbed, any softened soil or slough should be removed and replaced with crushed aggregate or additional concrete. In general, footing excavations should be cleaned such that no more than approximately ''/z-inch of loose soils are present prior to pouring concrete. Construction should include typical measures for controlling subsurface water beneath the homes, including positive crawlspace drainage to an adequate low point drain exiting the foundation, visqueen covering the exposed ground in the crawlspace, and crawlspace ventilation (foundation vents). The homebuyers should be informed and educated that some slow flowing water in the crawlspaces is considered normal and not necessarily detrimental to the home given these other design elements are incorporated into its construction. Appropriate design professionals should be consulted regarding crawlspace ventilation, building material selection and mold prevention issues, which are outside GeoPacific's area of expertise. 14835 SW 72ntl Avenue Tel(503) 598-8445 Portland, Oregon 97224 Fax(503) 941-9281 Elderberry Ridge - Lot 20 GeoPacific Project No. 15-4010 We have prepared this report for Riverside Homes, and it should not be relied upon by third parties without consulting GeoPacific. Within the limitations of scope, schedule and budget, GeoPacific attempted to execute these services in accordance with generally accepted professional principles and practices in the fields of geotechnical engineering and engineering geology at the time the report was prepared. The conclusions and interpretations presented in this report should not be construed as a warranty of the subsurface conditions. No warranty, expressed or implied, is made. The scope of our work did not include flood hazard evaluations, environmental assessments, the presence or absence of wetlands; or potential hazardous substances in the soil, surface water, or groundwater at this site. We appreciate this opportunity to be of service. Sincerely, GEOPACIFIC ENGINEERING, INC. PROp, �GIN�F� iQ 4/4 147 'E U OREGON ,4144/4/, .Ncro EXPIRES: 06/30/207k James D. Imbrie, G.E. Principal Geotechnical Engineer 2 GEOPACIFIC ENGINEERING, INC.