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 of the trenches. If water is encountered in the excavations, it should be removed prior to fill placement. Placement and compaction of recommended materials for utility trench backfill should be in accordance with the recommendations presented herein for Earthwork. In our opinion, the initial lift thickness should not exceed one foot unless recommended by the manufacturer to protect utilities from damage by compacting equipment. Light, hand-operated compaction equipment in conjunction with thinner fill lift thicknesses may be utilized on backfill placed above utilities if damage resulting from heavier compaction equipment is of concern. Grading and Drainage All exterior pavement finish grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks. Where paving or flatwork abuts the structure a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration. Gutters and downspouts should be routed into tightline pipes that discharge either directly into a municipal storm drain or to an alternative drainage facility. If drywells will be used for flow control of roof runoff of the building expansion, drywells should be located at least 25 feet beyond the expansion footprint and penetrate through any low permeability layers (such as the sandy silt layer encountered from 10 to 12% feet at boring B-2-20), into underlying layers of higher permeability. Department of Ecology regulations — including those established for treatment of stormwater runoff-- must be followed, including any treatment steps required prior to discharge. Earthwork Construction Considerations Shallow excavations for the proposed structure and inspection pit excavations are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of floor slabs and pavements. Construction traffic over the completed subgrades should be avoided to the extent possible. To the extent possible, the site should also be graded to prevent ponding of surface water on the prepared subgrades and excavations. Because the project site is entirely paved, temporary berms consisting of asphalt, sandbags bedded in a sealing compound (such as bentonite clay), or similar temporary water-stops could be constructed to re-direct stormwater flows away from the active construction site. Water collecting over, or adjacent to, construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted, prior to floor slab construction. Responsive • Resourceful • Reliable 8