5034 OCEAN AVE Geotech Report 2022-10-25

• southwest corner of the lot. It is our opinion that the exploration pits represent the subsurface conditions across the entire lot, Exploration pit(EP) logs of the completed explorations are attached to this report. The subsurface conditions consisted of a minor amount of fill soil or previously disturbed earth overlying Vashon aged advance outwash sand sediments. Stratigraphy The upper soils in all three explorations were comprised of topsoil or fill soil. The fill soil was comprised ofthe silt and.sand sediments from the leveling of the adjacent lot to the south. There was an excavation adjacent to the shop building on the adjacent south lot with the same sediment conditions as described below for the subject lot. The fill generally consisted of medin-m dense, dry to damp,light grey-brown, silty sand with some small gravels and organic fragments. The fill soils were found to be between 2 too feet thick in the three exploration pits. Underlying the fill soils were sediments consisting of medium dense to dense with increasing depth, dry to damp, light grey-brown, silty with some fine sand in the upper 1 to 2 feet grading to fine to medium sand with trace gravel extending beyond the termination depth of the pits. These sediments extended below the termination depths of our exploration pits at 6 to 7 feet below ground surface. This material was interpreted to be Vashon advance outwash sand that was deposited as an outwash alluvium in front of the advancing ice sheet during the last glacial advance into the Puget Sound region. The silt layer in the upper portion of the deposit represents an over-bank floodplain type deposit. The outwash sediments were subsequently over-run by several thousand feet of glacial ice resulting in a dense sediment with good strength and moderate permeability characteristics. Ground Water There was no ground water seepage encountered in the exploration pits at the time of our field explorations. We do not anticipate encountering any subsurface ground water conditions during the development of this project Surface runoff water appears to infiltrate through the site sediments with excess runoff flowing as sheet wash down slope. The sheet wash has not caused tilling or any other erosional features onsite. • Geologic Hazards The following discussion of potential geologic hazards is based on thevisual reconnaissance of the site, the subsurface explorations,and a review of aerial photographs and regional topographic maps of the area. Steep Slope and Landslide Hazards The site was located near the top of a historic drainage from an upland area down to the Puget Sound. The moderate slope of the top of this historic drainage channel was created by erosion through previous deposition rather than mass wasting events. The slope was comprised of dense, moderately free draining sediments with no evidence of past slope instability. It is our opinion that the slope is considered to be stable basedon current geotechnical engineering practice and the risk of slope instability is low: The development of a single family residence onsite will not affect the' BGC, olio 14267 209th Avenue NE Woodinville, WA 98077 (425) 273-5062