17 E MARINE VIEW DR 2019 Geotech Report 2025-10-01

PREVIOUS FIELD EXPLORATIONS AND LABORATORY TESTING Previous Field Exploration GeoEngineers previously evaluated the subsurface conditions for the Delta site for previous projects in 1991 and 2008.The 1991 field exploration program consisted of advancing two geotechnical soil borings (13-1 and MW-1), each advanced to a depth of 69 feet below existing ground surface.The field exploration program completed in 2008 consisted of advancing eight geotechnical soil borings (13-1 through B-8) to depths of 52 to 78 feet below existing ground surface.The approximate locations of the explorations are shown on Figure 2.Appendix A includes details of the previously completed exploration programs for the Delta site as well as the logs of the borings. Previous Laboratory Testing A laboratory testing program was completed for the soil samples collected in 1991 and 2008. Laboratory testing consisted of moisture content, sieve analysis, Atterberg limits, percent passing the US No. 200 sieve, and one-dimensional consolidation testing. The tests were performed in general accordance with test methods of the American Society for Testing and Materials (ASTM) or other applicable procedures. Appendix A includes relevant laboratory tests and test results from the previous studies at the site. SITE CONDITIONS Geology Geologic information for the project vicinity was obtained from the map prepared by Minard (1985). The entire site is mapped as being composed of younger alluvial and estuarine deposits associated with the Snohomish River and Puget Sound.These deposits consist of stratified sediments laid down by the streams and rivers in the area. The alluvial deposits consist of silt, sand and clay with organic matter. Glacial till, glacial outwash and transitional beds are mapped in the vicinity and are likely present below the alluvium. Although we did not review the site history,we anticipate that the site was constructed to current grade by dredging the Snohomish river sediments and placing them as fill on the site, as well as importing fill soil. Although not observed in the borings, glacial outwash and glacial till are mapped along the uplands in the vicinity of Marine View Drive.Glacial outwash is deposited by meltwater in front of the glacier as it advances or recedes. Cobbles, gravel, sand and silt settle out of the meltwater in stratified layers. Glacial outwash may or may not have been consolidated by the glacier. Glacial till is deposited directly by the glacier and typically consists of non-stratified deposits of silty sand with gravel and occasional cobbles and boulders. The till has been glacially consolidated and typically grades to dense to very dense at depth.The underlying non-glacial transitional beds typically consists of stratified silt, clay, and sand with occasional lenses or beds of gravel.The transitional beds have also been glacially consolidated and are medium dense to very dense or hard. Seismicity The Puget Sound area is located near the convergent continental boundary known as the Cascadia Subduction Zone (CSZ). The CSZ is the zone where the westward advancing North American Plate is overriding the subducting Juan de Fuca Plate. The CSZ extends from mid-Vancouver Island to Northern California. The interaction of these two plates results in two potential seismic source zones. These two seismic source zones are: (1) the Beniciff source zone, and (2) the CSZ interplate source zone. A third GEoENGINEERS August3,2018 Page2 File No.0643-015-00