9512 EVERGREEN WAY 2022-08-29 - Laserfiche WebLink

May 4, 2017 HWA Project No. 2017-036-21 Holly Drive from Evergreen Way. Northwest of the existing building, the ground slope steepens to about 8 percent, then to nearly 30% percent grade within about 6 feet of Holly Drive. A small terrace is situated in the southwest corner of the site that is about 6 feet higher than the Library building grade. Currently, the terrace accommodates a duplex residential structure which we understand will be removed to make room for the expanded parking area. The proposed new 5,860 square foot building expansion will consist of a single story, at -grade building extension, that will adjoin the northwestern wall of the existing library building as shown on Figure 2. 3.2 GENERAL GEOLOGY Geologic information for the project site was obtained from the published geologic map for the area entitled: Geologic Map of the Everett 7.5-Minute Quadrangle (Minard, 1985). The map indicates that the surficial geology of the subject parcel consists of Vashon till, a non -stratified and non -sorted mixture of clay, silt, sand, and gravel. The till was deposited as a deforming bed of reworked sediment beneath the glacial ice. It comprises a very compact unit due to the weight of the over-riding glacier. Cobbles are typically scattered throughout the till, and boulders are also often encountered. Vashon till soil has high shear strength and low compressibility, providing an excellent foundation medium for structures. Vashon till also exhibits relatively low permeability and, consequently, shallow infiltrating ground water often becomes perched above it. Locally, we expect the native till is overlain by fill soils composed of locally derived materials placed during site development. 3.3 SUBSURFACE CONDITIONS 3.3.1 Soil Conditions Based on the results of our exploration program, the native soil underlying the project area was observed to consist primarily of glacial till deposits. Following are descriptions of the soil deposits encountered in our explorations in the order of stratigraphic (depth) sequence by which they were deposited or placed, with the youngest unit described first. Detailed descriptions of the soils are presented in the exploration logs in Appendix A, and should be referenced for location specific information. Topsoil — Topsoil, consisting of loose to medium dense, silty sand with abundant organic material, was encountered at all locations except HH-2 and ranged from 0.25 to as much as 1.5 feet thick. Topsoil has low to very low shear strength, highly compressible, and moderately permeable. Fill — Fill, consisting of loose to medium dense silty sand, was identified at all locations except at HH-3 and ranged from 1 to 6 feet thick. This deposit appeared to be the result of local site grading predominately using native weathered till derived soils. At the location of HH-6, and to a lesser extent HH-2, fill consisted of imported gravel borrow and crushed surfacing top course. Final Geologic Assessment 3 HWA GeoSciences Inc.