4920 EVERGREEN WAY STAPLES Geotech Report 2022-10-25

Geotechnical Engineering Report lierracon Staples Rockery Failure Everett,Washington March 8, 2019 Terracon Project No. 81175122 Item Description Estimated Start of Construction Spring/Summer 2019 3.0 SUBSURFACE CONDITIONS 3.1 Geology The surficial geology is mapped as Qgt — Pleistocene continental glacial till when viewed using the Washington State Department of Natural Resources online application. The soil units observed were not consistent with the geologic mapped units and were predominantly undocumented fill underlain by advance outwash sands and gravels. The soil boring was performed to 561/2 feet below ground surface (bgs; see Exhibit A-3). Advance outwash, by definition, is glacially overridden with soils present in a dense to very dense state. The soil behind the rockery was observed to be loose to dense for the upper 23 feet and became dense to very dense with depth, despite little to no change in soil composition. We interpret the looser state of the soils to be a result of movements of the rockery that disturbed the portion of advance outwash behind the rockery resulting in the discrepancy of soil density. 3.2 Typical Profile Based on the results of the boring, subsurface conditions on the project site can be generalized as follows: Approximate Depth to Stratum Bottom of Stratum Material Description Consistency/ (feet) Density 1 8 yellow brown, fine to medium sand with loose trace silt and gravel (interpreted to be Fill) yellow brown with interbedded gray brown, 2 23 fine to medium sand with thin interbedded loose to dense silty sand layers (interpreted to be Disturbed Advance Outwash) yellow brown to light brown,fine to medium dense to very 3 38 sand with thin interbedded silty sand layers (Advance Outwash) dense reddish brown to gray brown, fine to coarse 4 Undetermined' sand and gravel with silt(Advance dense to very Outwash) dense Responsive { Resourceful M Reliable 3