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

generally greater on the northern portion of the site, closer to the river channel. Scattered woody debris was encountered in many of the explorations. Borings B-1 and B-5 (2008), encountered 2.5 to 5 feet of black wood shavings or wood chips at a depth of approximately 12.5 and 10 feet respectively. This wood waste is interpreted to be possible mill waste. Borings B-4 and B-4A show scattered brick and wire fragments and various debris at a depth of approximately 10 to 12 feet. Recent Alluvial Deposits Recent alluvial deposits underlies the fill soils.The recent alluvium generally consisted of loose to medium dense sand with variable amounts of silt and occasional gravel, wood and shell fragments. The recent alluvial deposits included interbedded estuary deposits which consist of silt and sand and variable amounts of organics.Recent alluvial deposits were encountered at depths ranging from 27.5 to 57 feet below ground surface in the southwest portion of the site(borings B-2, B-3, B-6, and B-7). In the northwest portion of the site (borings 13-1, B-4, B-5, and B-8) the boring logs show that the recent alluvial deposits were not fully penetrated within the explored depths. Estuary Deposits Generally finer grained sandy silt and silty sand estuary deposits were encountered in two primary layers within the recent alluvium. Estuary deposits were encountered in all borings except boring B-8.The estuary deposits were encountered at 12 to 22 feet below ground surface(approximately+3 to-11 feet)and 48 to 59 feet below ground surface(approximately-32 to-43 feet).The estuary deposits were typically very soft or very loose silt with sand,sand with silt and silty sand with occasional organic matter and shell fragments. The fine-grained portions of the samples were generally of low plasticity to non-plastic. Older Alluvium Generally denser granular soil, interpreted to be an older alluvial deposit,was encountered underlying the younger alluvium and estuary deposits.The older allium was observed in borings B-2, B-3, B-6, and B-7 at depths of 34 to 59 feet below ground surface. The older alluvium was visually similar to the younger alluvium, and typically consisted of dense to very dense sand with silt, but also included lesser amounts of dense silty sand and hard silt with sand. Groundwater The drilling method selected for the 2008 subsurface exploration program used drilling mud, which preludes the direct measurement the direct measurement of the groundwater table. Saturated soil conditions were observed at depths ranging from 5 to 14.5 feet below ground surface (Elevation +9 to 0 feet). The saturated soils that were encountered at depth are likely indicative of the groundwater table. We anticipate that the groundwater elevation will fluctuate in response to water levels in the Snohomish River. We also anticipate that the groundwater elevation will fluctuate as a function of precipitation, time of year,the tides and the surrounding surface water elevations,and other factors. CONCLUSIONS AND RECOMMENDATIONS Based on our evaluation of the previously completed subsurface exploration programs, it is our opinion that the proposed soil remediation facility may be constructed satisfactorily as planned with respect to geotechnical issues. A summary of the key geotechnical issues for the project is provided below. The GWENGINEERb� August3,2018 Page 5 File No.0643-015 00