600 RIVERSIDE RD Geotech Report 2022-10-25

1 1 1 -d 1 Landau Associates Laboratory soil testing was conducted on selected soil samples obtained from the test pits and borings to characterize certain engineering (physical) properties of the onsite soil. Testing was conducted in general accordance with appropriate American Society for Testing and Materials (ASTM) standards. The laboratory test results are presented in Appendix B. In addition, five near surface soil samples were submitted to SoilTest Farm Consultants, Inc. for agricultural soil analyses and four soil samples from borings B-1 and B-2 were submitted to ALS Global for analytical testing. The results of the agricultural soil analyses are presented in Appendix B and the results of the analytical testing are presented in Appendix C. Additional information regarding subsurface conditions in the vicinity of the project site was obtained from a review of boring and test pit logs from previous geotechnical and environmental studies performed at the site. The previous explorations generally confirm conditions observed in our current explorations and provide the opportunity to relate current subsurface conditions to subsurface conditions in the general area. Summary logs of these previous explorations are included for reference in Appendix D. The approximate locations of pertinent previous explorations are shown on the figures that precede the summary logs that are presented in Appendix D. Based on the results of our field and laboratory programs, the site is interpreted to be underlain by fill of varying depth that is underlain by native, fine to coarse, alluvial sand with silt, clayey silt, and pieces of wood. Based on the results of the subsurface explorations conducted as part of this and previous investigation, the thickness of the fill unit is expected to vary from 0 to about 20 ft. The onsite fill generally consists of dredged sand with areas of crushed rock, asphalt, concrete, and brick rubble, and wood debris. Others have reported encountering wood chips, industrial debris, and lime waste on the site. These types of fill material were not observed in the explorations completed as part of this study. 2.5 Groundwater Condition At the time of our field investigation in early March 2017, groundwater was observed at depths ranging from about 4.5 to 7.5 ft bgs in all of our explorations except test pit TP-413. Groundwater level data collected at various times throughout the years at the project site by LAI and others suggest that the depth to groundwater in most areas of the site is approximately 2 to 10 ft below the existing ground surface (LAI 2000). Reference to the existing ground surface refers to the ground surface that existed prior to site grades being raised during the site infrastructure phase of the project that was completed in the early 2000s. It should be noted that the groundwater conditions reported herein are for the specific locations and dates indicated, and therefore, may not necessarily be indicative of other locations and/or times. Furthermore, it is anticipated that groundwater conditions at the project site will vary depending on local subsurface conditions, the weather, the level of the Snohomish River, and other factors. It is likely that the highest groundwater levels will occur in the winter/spring months. Geotechnical Engineering Report Riverside Business Park Public Access Trails and Roadway Improvements 2-3 0121030.010.011 March 22, 2018 I