3800 RIVERFRONT BLVD Geotech Report 2023-05-04

March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 characterize the subsurface conditions across the site. The locations and designations of these borings are shown in the Site and Exploration Plan, Figure 2. Logs of the borings located across the site are provided in Appendix D. It should be noted that each of the subject borings were made prior to preloading and subsequent grading of the site. Therefore, geologic contacts shown in these borings have changed position due to surcharging of the site. HWA also utilized several geotechnical borings associated with other studies. Borings BH-101 and BH-105 through BH-107 that were drilled by HWA in support of the 3-Acre Park development (HWA, 2018), where utilized. These borings were drilled within the 3-Acre Park site and near Lift Station 33. Boring BH-107 was drilled from a barge in the Snohomish River. HWA utilized one geotechnical boring, designated MW-36, that was drilled by HWA in support of water quality monitoring for the landfill site(HWA, 2012). Lastly, HWA utilized one boring, designed B-201, that was drilled by HWA in support of the design of the various public amenities along the river(HWA, 2012). The approximate locations of these borings are indicated on Figure 2 and their logs are provided in Appendix E. These borings are located outside of the Project Evergreen boundary but were used for slope stability and lateral spreading evaluations. 3.0 GENERAL SITE CONDITIONS 3.1 SITE TOPOGRAPHY AND HISTORY The Riverfront Development site is located within the limits of the Old Everett Landfill and is bounded on the west by the Burlington Northern Santa Fe Railway(BNSF)rail lines, on the north by 36th Street and on the east by the Snohomish River. For over 50 years the Old Everett Landfill accepted municipal solid waste until its eventual closing in 1975. The site remained relatively dormant from 1975 to 2008 at which time efforts began to prepare the site for development. From 2008 to 2012 the site underwent severalphases of surcharging meant to 111 p g g consolidate the underlying refuse and alluvial deposits. After completion of surcharging, the site was graded to its current configuration and the upper 18 inches of soil, across portions of the site, was cement-treated to develop an all-weather construction surface. In the summer of 2018, additional Common Borrow fill was placed across the site to raise grade by approximately 3 feet. Most of the site is currently relatively flat with a slight slope to the east. The eastern edge of the site slopes downward at a 2 to 1 slope to the edge of the landfill. 3.2 GENERAL GEOLOGIC CONDITIONS The geology of the Puget Sound region includes a thick sequence of over-consolidated glacial and unconsolidated non-glacial soils overlying bedrock. Glacial deposits were formed by ice originating in the mountains of British Columbia (Cordilleran Ice Sheet) and from alpine glaciers which descended from the Olympic and Cascade Mountains. These ice sheets invaded the Puget Lowland at least four times during the early to late Pleistocene Epoch (approximately 2.4 million to 10,000 years before present). The southern extent of these glacial advances was near Tenino, Washington. During periods between these glacial advances and after the last glaciation, Geotechnical Report Revision 3 26 2019.doc 4 HWA GEOSCIENCES INC.