7800 EVERGREEN WAY HYUNDAI Wetland Report 2025-08-05

■ The contractor should take necessary measures to prevent on -site soils and soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps, and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the surficial soils by rolling with a smooth -drum roller prior to periods of precipitation will help reduce the extentthatthese soils become wetor unstable. ■ The contractor should cover all soil stockpiles that will be used as structural fill with plastic sheeting. ■ Construction trafficshould be restricted to specific areas of the site, preferably areas that are surfaced with the existing asphalt or working pad materials not susceptible to wet weather disturbance. ■ Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical. Routing of equipment on the on -site fill and existing native subgrade soils during the wet weather months will be difficult and the subgrade will likely become highly disturbed and rutted. In addition, a significant amount of mud can be produced by routing equipment directly on the on -site soils in wet weather. Therefore, to protect the subgrade soils and to provide an adequate wet weather working surface for the contractor's equipment and labor, we recommend that the contractor protect exposed subgrade soils with sand and gravel, crushed gravel, orATB. 4.7.4. Utility Trenches Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures described in the 2020 WSDOT Standard Specifications or other suitable procedures required by the City of Everett or specified by the project civil engineer. The native glacial deposits and fill soils encountered atthe site are generally of low corrosivity based on our experience in the Puget Sound area. Utility trench backfill should consist of structural fill and should be placed in loose lifts not exceeding 12 inches in thickness when using heavy compaction equipment and not more than 6 inches when using hand -operated compaction equipmentsuch thatadequate compaction can be achieved throughoutthe lift. Each lift must be compacted priorto placingthe subsequent lift. Priorto compaction, the backfill should be moisture conditioned to within 2 percent of the optimum moisture content, if necessary. The backfill should be compacted in accordance with the criteria discussed above. Figure 4 illustrates recommended trench compaction criteria under pavement and non-structural areas. 4.7.5.Sedimentation and Erosion Control In our opinion, the erosion potential of the on -site soils is low to moderate. Construction activities including stripping and gradingwill expose soils to the erosional effects of wind and water. The amountand potential impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather construction will increase the amount and extent of erosion and potential sedimentation. Erosion and sedimentation control measures may be implemented by using a combination of interceptor swales, straw bale barriers, silt fences and straw mulch for temporary erosion protection of exposed soils. All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion. Erosion and sedimentation control measures should be installed and maintained in accordance with the requirements of the City of Everett. GEOENGINEER� December6, 2021 Page 11 File No. 24 59-003-00