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

• Geotechnical Engineering Report lierracon Merrill Creek Operations Base Expansion x• Everett, Washington December 14, 2020 r Terracon Project No. 81205012 GeoReport Item Description The project site consists of existing rigid pavement at the west end of the existing operations and maintenance building —this building occupies a footprint of approximately 57,500 square feet and comprises the largest building on the greater Community Transit campus (other CT buildings are Site Information and situated to the east and south). The proposed building expansion will Existing increase the existing operations and maintenance building by about 16,550 Improvements feet, add several bays for coach maintenance, painting, equipment and materials storage, and related coach fleet activities. Renovation and reprogramming of these activities within the western portion of the existing building footprint will also occur. See Site Location Project site is flat and paved with concrete pavement. This topography is a result of previous site filling, which occurred in the mid-1980s to early-1990s, following aggregate mining and processing activities in the 1960s and 1970s. Fill is presumed to have been derived largely from flattening of the slope above the site to the west. Existing Topography Prior to construction of the existing building in 1996/1997, re-working and re- and Site History compaction of upper portions of the fill — plus placement of additional fill occurred, resulting in the dense to very dense upper layer of fill encountered (as discussed below). A greater discussion of site history, previous explorations, and fill placement is presented later in this section. • Dense to very dense silty sand fill with gravel to depth of about 12 feet (below existing grade)was observed at both exploration locations. • Below 12 feet, additional fill consisting of silty sand was encountered; soil density is variable below 12 feet and ranges from loose to very Geology dense. ✓ Native advance outwash was encountered near the bottom of the deeper boring, below a depth of 40 feet. • Groundwater was encountered at a depth of 27 feet below the ground surface. Site History Based on Washington Geologic Information portal, the site geology is mapped as Vashon Advance Outwash, although this native soil was encountered only at considerable depth in our deeper exploration. The sand and gravel of this outwash soil unit were historically mined for concrete and asphalt aggregate and other building materials; mining of aggregates occurred on-site from at least as early as the early 1960s through the early 1970s. Between about 1986 and 1990, excavations were filled in by flattening of surrounding high banks around the pit and by "borrowing" of soil from the slope to the Responsive • Resourceful z Reliable