6617 ASSOCIATED BLVD AMAZON Geotech Report 2022-10-25

• • n • NFELDER • • Native soils underlying the existing fill also consisted of silty sand with variable gravel content • and were found to be medium dense to very dense. The site geology, observed subsurface • conditions, and SPT blow counts indicate that the native material is ablation till from the Vashon • Stade of the Fraser Glaciation. Detailed descriptions of the soils are provided on the boring logs • presented in Appendix A. Ablation till, also referred to as melt-out till, is a glacial drift unit that • occurs when glacial ice melts and deposits the previously suspended load of silt, sand, gravel, • cobbles and boulder size particles in the footprint of the glacial ice. Ablation till deposits are • typically underlain by the more compact, lodgment till glacial drift unit. • • Groundwater was encountered in all borings and was generally observed at or near the contact • interface of existing fill soils and native till soils (approximately 3 to 7 feet below the ground • surface). The observed conditions indicate that the groundwater may be perched on the • underlying denser, less permeable ablation till, and may not represent the level of the local • groundwater table. Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. • Therefore, groundwater levels during construction or at other times in the life of the structure • may be higher or lower than the levels indicated on the boring logs. The possibility of • groundwater level fluctuations should be considered when developing the design and • construction plans for the project. • • • • • • • • • • • • • 20203884.001A/SEA20R110164 Page 8 of 28 June 1, 2020 • ©2020 Kleinfelder •