600 RIVERSIDE RD Geotech Report 2022-10-25

Landau Associates A soil containment area (Containment Area A-2) is located near the eastern end of the road/bridge that provides access to the project site. The trail that is proposed as part of this project will cross a portion of Containment Area A-2. Provided below is some information related to this soil containment area, as well as information to keep in mind when designing and constructing the portion of the trail that crosses the containment area: • The cap over Containment Area A-2 consists of a geosynthetic clay liner (GCL) with about 2.5 ft of soil cover • It is acceptable to construct a paved trail over Containment Area A-2 • If site grades need to be raised to construct the proposed trail, it is acceptable to place fill over Containment Area A-2 • If site grades need to be lowered to construct the proposed trail, it is acceptable to remove some of the soil that is currently on top of the GCL, provided a minimum of 1 ft of soil cover is maintained over the GCL • The only other restriction with respect to constructing a trail over a portion of Containment Area A-2 is that the existing GCL cannot be penetrated. 3.9 Agricultural Soil Analyses As previously noted, SoilTest Farm Consultants under subcontract to LAI performed a series of agricultural soil analyses on 5 near surface soil samples that were collected by LAI personnel along the proposed trail alignment at the approximate locations illustrated on the Figure 2 of this report. Based on the results of this analysis, SoilTest Farm Consultants developed recommendations related to what soil amendments are needed to support growth of the plants proposed along the trail alignment (at -grade riparian plants native to western Washington). The results of this testing and SoilTest Farm Consultants' recommended soil amendments are presented in their reports, which are attached to the end of Appendix B. It is our understanding that the project's landscape architect (Macleod Reckord) desires a planting soil for the plants proposed along the trail alignment that contains between 2 and 5 percent clay and between 10 and 20 percent silt. Based on the gradation of the 5 agricultural soil samples analyzed by SoilTest Farm Consultants, the following amounts of sand (presented in terms of pounds of sand per ton of existing soil that is treated) could be added to the onsite soil to satisfy the above described silt content requirement. Geotechnical Engineering Report 0121030.010.011 Riverside Business Park March 22, 2018 Public Access Trails and Roadway Improvements 3-13 1 u I