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 The infiltration test pits were excavated to the approximate depth of the proposed infiltration facility to conduct the PIT. After completion of the PIT, the exploration pit was overexcavated to allow observation of the subsurface conditions beneath the infiltration test. The explorations permitted direct, visual observation of subsurface conditions. Materials encountered in the explorations were studied and classified in the field by a geologist from AESI. After logging the exposed soils, the explorations were backfilled with the excavated soil and lightly tamped with the excavator bucket. Disturbed soil samples were selected from the pits, placed in moisture-tight containers, and transported to AESI's laboratory for further visual classification and testing, as necessary. The exploration logs in the Appendix are based on the field observations and inspection of the samples. 3.2 Exploration Boring and Monitoring Well A monitoring well, MW-1, well. tag BKC253, was completed on December 15, 2017, by Holocene Drilling under subcontract to AESI. Holocene Drilling is licensed in the State of Washington in accordance with Washington Administrative Code (WAC) Chapter 173-160. The exploration boring was logged and the construction of the monitoring well was observed by experienced AESI staff. Drilling for the installation of MW-1 was performed with an 8-inch outer diameter/4-inch inner diameter, hollow-stem auger. Samples were taken at 2.5-foot intervals to a depth of 30 feet, and at 5-foot intervals to 75 feet, using the Standard Penetration Test (SPT) procedure in accordance with the American Society for Testing and Materials(ASTM) D-1586). The SPT testing and sampling procedure consists of driving a standard, 2-inch outside-diameter, split-barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded, and the number of blows required to drive the sampler the final 12 inches represents the Standard Penetration Resistance (also known as the "N-value"). If a total of 50 blows is reached within one 6-inch interval, the N-value is recorded as 50 blows for the corresponding number of inches of penetration. The N-value provides a measure of the relative density of granular soils or the relative consistency of cohesive soils. N-values are presented on the exploration boring log presented in the Appendix. The samples obtained from the split-barrel sampler were classified in the field, and representative portions were placed in watertight containers. The samples were then transported to our laboratory for further visual classification and/or testing. Soil descriptions shown on our exploration log are based on N-values, drilling action, field observations, and laboratory classifications. The monitoring well was completed with a total depth of approximately 74.4 feet, and encountered groundwater in advance outwash sediments at approximately 60 feet below February 26,2018 ASSOCIATED EARTH SCIENCES,INC. AWR/ms-170671E001-2-Projects\201706711KE\WP Page 3