6202 ASSOCIATED BLVD Geotech Report 2022-10-25

Proposed Everett Warehouse Project No. 2152.01 March 5, 2019 Hydraulic compaction of soils beneath infiltration facilities could result in settlement and damage of improvements located in the vicinity of infiltration facilities. As such, it is our opinion stormwater infiltration is not feasible for this project. Site Preparation Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments. We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion, whereas soil stockpiles should be protected with anchored plastic sheeting. Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into and/or over excavations. Exposed grades should be crowned, sloped, and smooth -drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. Equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Clearing, Stripping, and Existing Utility Abandonment: Once TESC measures are installed, we expect site preparation to continue with clearing and grubbing brush and trees, stripping of organic rich topsoil, an abandonment of existing underground utilities. We recommend all tree stumps and roots larger than inch in diameter be cleared and grubbed from the areas planned for improvement. Based on our explorations, stripping depths to remove topsoil is estimated to range from about 3 to 10 inches. Stripping depths maybe greater near trees and brush to fully remove root systems. All clearing and stripping debris should be wasted off site or, if approved, used for topsoil in landscape areas. For utility abandonment, we recommend all existing underground utilities be completely removed and wasted off site. Excavations for utility abandonment should be backfilled with compacted structural fill placed in accordance with this report. Alternatively, existing underground utility piping could be abandoned in -place by fully grouting the conduits. Subgrade Preparation: Once site preparation is complete, all areas that are at design subgrade elevation or areas that will receive new structural fill should be moisture conditioned to a moisture content within plus or minus two percent of optimum moisture content for compaction. The subgrade should then be compacted to a firm and unyielding condition. Much of the existing site soils consist of and with an appreciable amount of silt content above optimum moisture content for compaction. During wet weather, achieving a moisture content adequate for Page 6