9900 19TH AVE SE Geotech Report 2018-01-02 MF Import

Geotechnical Engineering Report Home Base Warehouse - Everett July 31, 1997 NCA File No. 213497 Page 4 enough to extend to the bottom of the planned excavation for the detention vault and on -site detention pond. The soil beneath the bottom of the test pits is glacially consolidated, and will provide good support for overlying structures and fill. However, we were not able to observe soil type or ground water conditions beneath the depths explored. We recommend that the contractor complete explorations ("potholes") in these areas to better evaluate soil and ground water conditions at the planned depths of construction before starting major earthwork. r The test pits were located in the field by a geologist with this firm, who classified the soils encountered and maintained logs of the explorations. The test pit and hand probe locations are shown on the Site Plan i in Figure 2. The soils were visually classified in general accordance with the Unified Soil Classification j System: as shown in Figure 3. The samples were brought back to our laboratory for further classification. Logs of the test pits are presented in Figures 4 through 9. Or:r explorations encountered a surfcial layer of topsoil about 0.4 to 2 feet in thickness. The topsoil consisted of loose, silty sand with roots and organics, and trace gravel. We probed at seven locations in aid around the wetland with a 1/2-inch diameter steel probe. The soils at these locations probed dense at r appr;,a imately 2 to 3 feet. We expect the looser soils above 2 to 3 feet deep in the wetland to be topsoil an.1/or weathered native soils. We encountered a 1.3 to 3.4 foot thick layer of loose to medium dense, brown silty fine to medium sand with gravel, roots, and varying amounts of cobbles underlying the topsoil to depths ranging from 2.3 to 4.0 feet below the surface. We interpret this to be weathered glacial till. We encountered unweathered itill underlying the weathered glacial till. It consisted of dense to very dense, gray -brown to gray, silty fine and fine to medium sand with gravel, scattered cobbles, seams of fine to medium sand with silt, and I occasional seams of gray silt with fine sand and gravel. The till graded to very dense, gray silt with fine f sand, gravel, and lenses of silty sand with gravel in Test Pit 6. We included this silt with the till in our Jinterpretation; however, it may be a part of the advance outwash. 1 Test Pits 5 and 11 encountered dense, gray, fine to coarse and fine to medium sand with varying amounts of silt, gravel, and scattered cobbles underlying the glacial till. We have interpreted these soils to be l advance outwash deposits. We expect the outwash underlies the entire site at depth. NELSON-COUVRETTE & ASSOCIATES, INC. I