2514 RAINIER AVE Geotech Report 2022-10-25

I i ,.._ :, 1` Ifoster wheeler 111 The strata observed in our explorations are described below. ► Topsoil and Organics: In general, all explorations advanced in nonpaved areas I encountered approximately 3 to 4 inches of grass/sod over topsoil at the surface. Boring B-2, advanced at the south end of the athletic field, encountered a 1-foot layer of relic topsoil at the fill-native contact horizon 3.5 to 4.5 feet below ground surface (bgs). I ► Existing Fill: A variable amount of fill ranging from approximately 1 to 5.5 feet thick was encountered in all of our borings (B-1 through B-6). The fill was generally composed of I loose to medium dense, brown to gray to dark gray, silty sand or sandy silt containing variable amounts of gravel, organic matter, and debris. The fill appeared to be originally derived from the on-site glacial soils. We interpret the majority of the fill soils encountered were placed during school campus construction. I ► Lacustrine Silts: Below the fill, borings B-1 through B-6 encountered soft to very stiff fine sandy silt to depths of 10 to 18.5 feet bgs. I ► Advance Outwash: The Advance Outwash was composed of dense to very dense gravelly sand or silty sand that contained a variable silt content. Borings B-1, B-2, and B-5 I encountered Advance Outwash at 15 to 17 feet bgs, while B-3 encountered the Advance Outwash at 10 feet bgs. Borings B-4 and B-6 encountered an obstruction and driller refusal at 15 feet and 18.5 feet bgs, which appeared to be a medium to large size rock (cobble or boulder). Because such sized rocks are not common in fine-grained lacustrine deposits, Iwe interpreted the obstruction depth to be at the Advance Outwash contact. Table 2 Summary of Soil Conditions IDepth to Elevation of Elevation of Dense Stiff Dense Thickness of Depth to Stiff Advance Lacustrine Advance I Boring Fill Lacustrine Outwash Silts Outwash ID (feet) Silts(feet) (feet) (feet) (feet) B-1 4.5 7.5 17.0 74.5 65.0 IB-2 4.5 4.5 15.0 76.5 66.0 B-3 1.0 1.0 10.0 75.5 66.5 B-4 1.5 1.5 15.0 76.5 63.0 I B-5 3.5 3.5 15.5 72.5 60.5 B-6 5.5 6.0 N/E N/E N/E= Not Encountered I Elevation datum: NAVD88(Vertical)and NAD 83/91 (Horizontal) per North Middle School Modernization Plan Set by Coughlin Porter Lundeen, dated August 29,2017. I The exploration logs included in Appendix A provide a detailed description of the soil strata encountered in our subsurface explorations. The enclosed Site and Exploration Plan (Figure 2) shows the location of each boring. Table 2 summarizes the soil conditions encountered in our explorations. I IAmec Foster Wheeler Project No.6-917-18116-0 5 I \\Sea-fs1\WordProc\ Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx