4730 COLBY AVE YMCA Geotech Report 2025-04-14

Subsurface Exploration, Geologic Hazard, and Snohomish County YMCA Geotechnical Engineering Report Everett, Washington Project and Site Conditions ground surface at the time of drilling. Following drilling, a groundwater monitoring well was installed in MW-1 to allow for documentation and long-term monitoring of groundwater levels below the subject site. This well consists of a 2-inch-diameter polyvinyl chloride (PVC) Schedule-40 well casing with threaded connections. The lower 10 feet of the well is a finely-slotted (0.020-inch machine slot) well screen to permit water inflow. The annular space around the well screen was backfilled with silica sand and the upper portion of annulus was sealed with bentonite chips. A flush-mounted steel monument was placed over the top of the wellhead for protection. The as-built configuration of this well is illustrated on the boring log in the Appendix. AESI developed the well by surging and pumping to improve the hydraulic connection between the well and the aquifer.AESI installed a digital pressure transducer in the well to monitor the water level. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, review of explorations completed by others, visual reconnaissance of the site, and review of selected geologic literature. The general distribution of geologic units is shown on the exploration logs. The explorations typically encountered existing fill soils underlain by Vashon lodgement till over Vashon advance outwash. 4.1 Stratigraphv Grass/Bark/Gravel Surfacing/Topsoil A surficial layer of grass,bark, gravel surfacing overlying organic topsoil was encountered at the location of six of the exploration locations. This organic topsoil layer ranged from approximately 4 to 6 inches in thickness. Excluding the gravel surfacing,these materials are not considered suitable for foundation, roadway, or slab-on-grade floor support, or for use in a structural fill due to their high organic content. Gravel surfacing may be reused as structural fill if such reuse is specifically allowed by project plans and specifications, if excessively organic and any other deleterious materials are removed, and if moisture content is adjusted to allow compaction to the specified level and to a firm and unyielding condition. Existing Asphalt Existing asphalt surfacing was encountered in Explorations EB-1, EB-6, and EB-8. In EB-1, the asphalt was 2 inches thick and was underlain by 2 inches of a crushed rock base course. In EB-6 and EB-8, our borings encountered 1 inch of asphalt overlying 1.5 inches of a crushed February 26,2018 ASSOCIATED EARTH SCIENCES,INC. AWR/ms-170671E001-2-Projects\201706711KE\WP Page 4