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The Mark at Eugene January 6, 2026 Geotechnical Investigation and Seismic Hazard Study 8 Project No.: 2251077 Eugene, Oregon Landmark Construction, LLC Based on our observations at the site, laboratory testing and understanding of the proposed grading, we do not believe mitigation of the clay is warranted. This evaluation assumes the drainage improvements and use of thickened granular layers to support new foundations and slabs will be implemented. Seasonal and Construction Timing Considerations The native soils are moisture-sensitive and prone to softening and pumping in the presence of moisture and construction activities. To reduce the risk of subgrade softening and pumping, we recommend completing the earthwork and foundation construction during the typically dry summer months (typically mid-June through September) when there is typically sufficient sustained dry weather. We understand construction is currently planned to start next summer. The parcel includes limited access, and we anticipate at-grade portions will support heavy construction equipment extending into wet weather. Therefore, mitigation measures will be required to protect the subgrade. Typical mitigation measures may include thickening the base rock section in pavement areas, construction haul roads, or other areas subjected to repeated construction traffic. The required thickness will depend on the anticipated traffic and construction schedule. A minimum of 24 inches should be anticipated for the building pad to support construction equipment during wet weather. The actual rock thickness should be determined at the time of construction based on weather conditions, schedule, and proposed construction traffic. Drainage As discussed in a previous section of this report, groundwater is expected to be relatively shallow throughout the year and may be near the ground surface during periods of wet weather. Shallow groundwater levels are a design concern for any below-grade structures, including retaining walls and elevator pits. The structures would need to be designed to accommodate the hydrostatic and buoyancy forces associated with shallow groundwater at the site. Typically, foundation drains would be installed to mitigate any hydrostatic pressures around the below-grade structures. If drainage is not practical, the structure will need to be designed to accommodate the hydrostatic pressures for any retaining walls and buoyancy for structures, such as elevator pits, extending below grade. In addition, additional detail and consideration will need to be provided for waterproofing and the slab vapor barrier.