10901 27TH AVE SE Geotech Report 2025-07-29

1 ' Subsurface Exploration, Geologic Hazards, and Proposed James Monroe Elementary School Replacement Revised Geotechnical Engineering Report Everett, Washington Project and Site Conditions Fill Existing fill was encountered in three of our explorations to maximum depths of approximately 5 feet below the existing ground surface. Existing fill is not suitable for structural support without remedial preparation as described in the "Site Preparation" section of this report. ' Existing fill should be replaced below planned building areas, and should be re-worked under paving. Excavated existing fill material is suitable for reuse in structural fill applications if it is free of excessive organic material and other deleterious materials. ' Lodgement Till Below the surficial fill where it was present, all of the exploration borings encountered medium ' dense grading to very dense, silty sand with gravel interpreted as Vashon lodgement till. Lodgement till was deposited at the base of an active continental glacier and was compacted by the weight of the overlying glacial ice. Lodgement till is suitable for structural support when properly prepared. Excavated lodgement till material is suitable for use in structural fill applications if suitable moisture conditions are achieved, which will require drying during ' favorable dry weather. At the time of exploration, we estimate that most of the lodgement till soils that we observed were above or near optimum moisture content for compaction purposes. ' Published Geologic Map We reviewed published geologic mapping for the project (Distribution and Description of the Geologic Units in the Everett Quadrangle, Washington, by James P. Minard, 1981). This map indicates that the site is expected to be underlain at shallow depths by Vashon lodgement till. Advance outwash is mapped at lower elevations to the northeast. ' 4.2 Hydrology ' No free ground water was observed in any of the borings completed for this study. Relatively high moisture contents were observed in existing fill above the native sediments. At this site, ground water seepage should be expected to develop seasonally close to the interface between surficial fill and/or weathered native soils and the underlying lodgement till sediments. Such perched ground water is common and is typically addressed on construction sites by use of interceptor swales or other similar methods. ' 4.3 Laboratory Testing ' We completed two laboratory grain size tests for this study. We selected representative samples of surficial weathered lodgement till and deeper less weathered lodgement till. Test results are included in the Appendix. ' October 5, 2009 ASSOCIATED EARTH SCIENCES, INC. t3WG/Id-KE09031243 Projecrs1300903121KE WP Page 4 i