10930 HOLLY DR Geotech Report 2025-08-08

Helix Design Group,Inc.-Greenwood Heating&Air Conditioning,Everett,WA April 22,2022 Geotechnical Engineering Report Z0219 4.0 CONCLUSIONS AND RECOMMENDATIONS Improvement plans involve the clearing/stripping/grading of the subject property, and the construction of a one-story, 10,000-sf warehouse building adjoined to a two-story, 5,000-sf office building towards the central portion of the property. The new structures will be encircled by extensive asphalt pavements for drive lanes and parking facilities to support 50 to 60 vehicles. Site produce stormwater will be retained onsite if feasible, with the northeast corner of the property being reserved for stormwater management. We offer these recommendations: • Feasibility: Based on our field explorations,research and analyses,the proposed structures appear feasible from a geotechnical standpoint. • Foundation Options: Foundation elements should be constructed on medium dense or denser undisturbed native soils, or on structural fill bearing pads that extend down to medium dense or denser native soils. We anticipate that adequate bearing soils will be encountered at relatively shallow depths (less than 2 feet) across much of the proposed building area. Recommendations for Spread Footings are provided in Section 4.2. • Floor Options: Floor sections should bear on medium dense or denser native soils or on properly compacted structural fill that extends down to medium dense or denser native soil. We anticipate that adequate bearing soils will be encountered at relatively shallow depths(less than 2 feet)at the proposed building area,and we do not foresee the need for a granular fill subbase. Existing fill soil should largely be suitable for support of slab-on grade-floors. Organic laden material should be removed from the slab subgrade. Recommendations for slab-on-grade floors are included in Section 4.3. • Pavement Sections: Native,in-situ soil conditions are amenable to the use of soil-supported pavements. We recommend a conventional pavement section comprised of an asphalt concrete pavement over a crushed rock base course over a properly prepared(compacted) subgrade or a granular subbase, depending on subgrade conditions during pavement subgrade preparation. All soil subgrades should be thoroughly compacted,then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over-excavated to a depth of 12 inches and replaced with a suitable structural fill material. • Infiltration Conditions: Given the geologic conditions underlying the subject property,we do not interpret infiltration as being feasible for this project. We recommend that site produced stormwater be diverted to an existing system along Airport Rd, or managed through detention,or other appropriate means. • Geologic Hazards: During our site reconnaissance, advancement of subsurface explorations,and general evaluation of the proposed development,we did not observe any erosional, landslide, seismic, settlement, or other forms of geologic hazards within the subject property. Given this fact,we recommend that no buffers,setbacks,or other forms of site restraints be implemented to address these potential hazards. Migizi Group,Inc. Page 7 of 16 ilf