1029 52ND ST SW Geotech Report 2022-10-31

4.1 SURFACE CONDITIONS The site is located northeast of the intersection of Seahurst Avenue and 52nd Street SW in Everett, Washington. Based on preliminary site plans provided by ASPI, the site slopes down to the east with an overall grade change across the site of approximately 22 feet. The west side of the site is currentlydeveloped with two single-family residences and one detached garage. The east side of the site is generally undeveloped and covered with trees and underbrush. The ground surface is generally covered with thin grass and topsoil layer. 4.2 SUBSURFACE CONDITIONS Subsurface conditions at the site were evaluated by reviewing geologic maps and excavating five test pits: We anticipate the base of the infiltration elements will be approximately 1.5 feet BGS. The geologic map of the project area indicates that glacial till is the predominant geologic unit underlying the site. Glacial till deposits in this area are typically composed of dense to very dense, silty sand with gravel, cobbles, and boulders (Minard, 1985). Our subsurface exploration program consisted of excavating five test pits. Small-scale PITs were performed in two of the test pits. The approximate test pit locations are shown on Figure 2. The test pits were excavated using a rubber-tracked excavator. The test pits were excavated to depths between 4.0 to 10.0 feet BGS. For TP-3 and TP-5, excavation was stopped at a depth of 1:5 feet BGS to conduct a small-scale PIT as discussed in the"Infiltration Testing"section. A description of the field explorations and logs of the explorations are presented in Appendix A. The soil observed during our explorations is discussed in the following sections. 4.2.1 Grass/Topsoil/Root.Zone A grass, topsoil, and root zone layer,is present at the surface of all test pits. This layer is generally 1 foot in thickness and underlain by fill material. • • 4.2.2 Fill Fill material is present beneath the grass and topsoil layer across the site. The fill material consists of a loose, gray-brown, silty sand with gravel that appears to be locally derived. The fill varies in thickness from 1.5 to 3.0 feet and is underlain by dense glacial till. 4.2.3 Glacial Till Dense to very dense gray glacial till is present beneath the fill material in all test pits.The glacial till consists of silty sand with gravel and cobbles. All of the test pits were completed within the glacial till. 4.3 GROUNDWATER Groundwater was not encountered during our explorations that extended to depths of up to 10.0 feet BGS. G EODESIGN= 2 NWHome-1-01 a 01618