7100 HARDESON RD SITE DEVELOPMENT Geotech Report 2025-03-04

Geotechnical Engineering Report lierracon Merrill Creek Operations Base Expansion • Everett, Washington - December 14, 2020 • Terracon Project No. 81205012 GeoReport. Model Layer Layer Name — General Description 1 PCC Rigid Portland cement concrete pavement 2 Base Granular base layer supporting pavement 3 Dense Fill Dense to very dense silty sand fill 4 Variable Fill Silty sand and sandy silt of variable density/consistency 5 Outwash j Native glacial outwash consisting of fine to medium sand Groundwater Conditions The boreholes were observed while drilling and shortly after completion for the presence and level of groundwater. Groundwater was not encountered in boring B-1-20, which was advanced to a depth of 26'/2 feet. Groundwater was encountered in boring B-2-20 at a depth of 27 feet. Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project. GEOTECHNICAL OVERVIEW As discussed in the Site Conditions, previously placed fill is on site within the footprint of the proposed building expansion. Support of foundations, floor slabs, and pavements on or above existing fill materials is discussed in this report. However, even with the recommended construction procedures, there is inherent risk for the owner that compressible fill or unsuitable material, within or buried by the fill, will not be discovered. Although previous site preparation in the mid-1990s reportedly included re-working and re-compaction of site fill —and our explorations encountered dense to very dense fill to a depth of about 12 feet in both borings -- this risk of concealed softer/looser fill cannot be eliminated without completely removing the existing fill but can be reduced by following the recommendations contained in this report. To take advantage of the cost benefit of not removing and replacing the entire amount of previously placed fill,the owner must be willing to accept the risk associated with building over the previously placed fill. The near surface dense to very dense silty sand soils are suitable for support of conventional spread footings and concrete slab-on-grade floors; however, if grading is performed during the winter months, an increased risk for subgrade disturbance and poor subgrade performance is likely, and subgrade remediation is likely to be necessary. Additional site preparation recommendations for wet weather are provided in the Earthwork section. The General Comments section provides an understanding of the report limitations. Responsive • Resourceful • Reliable 5