6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration, Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Design Recommendations discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. Final exterior grades should promote free and positive drainage away from the building at all times. Water must not be allowed to pond or to collect adjacent to the foundation or within the immediate building area. It is recommended that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeter be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structures. Additionally, pavement subgrades should be crowned to provide drainage toward catch basins and pavement edges. 14.0 RETAINING WALL CONSIDERATIONS A retaining wall with a maximum height of about 18 feet will be required at the north end of the parking lot to achieve final grade near an existing wetland area and eastern property line. The wall type is not known at this time. Retaining walls are feasible for the project when founded on medium dense to dense glacial till soils. Feasible wall types for this project could include gravity block walls, mechanically stabilized earth (MSE) walls, or cast-in-place concrete cantilever walls. We are available to provide geotechnical design recommendations for specific wall types and heights as the project design develops. 15.0 PRELIMINARY PAVEMENT RECOMMENDATIONS We anticipate that the project will include heavy-duty pavement areas for the entrance driveway and the truck parking surrounding the new building, and light-duty pavement areas for employee parking. The pavement for this project is expected to be supported by either medium dense to dense native soils or new structural fill. Once final subgrade is reached for the entrance driveway and parking lot areas, we recommend that the subgrade be proof-rolled under the observation of AESI with a loaded dump truck or other suitable equipment to identify any soft areas prior to placement of the base course. The design of a pavement is dependent on the traffic volume, type and weight of vehicles, and the soil subgrade strength. Until traffic volume data becomes available for the project, we recommend the following preliminary heavy-duty sections based on the Washington State Department of Transportation (WSDOT) Pavement Policy Manual for access roads and truck parking areas. • For heavy-duty asphalt pavement, we recommend a preliminary section that consists of 6 inches of hot mix asphalt (HMA) over 6 inches of 11/4-inch crushed rock base course meeting WSDOT Standard Specifications. The upper 1 inch of 11/4-inch crushed rock can December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEl/Id-20200319E001-002 Page 16