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■ The contractor should take necessary measures to prevent on-site soils and soils to be used as fill from <br /> becoming wet or unstable.These measures may include the use of plastic sheeting,sumps with pumps, <br /> and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the <br /> surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will help reduce the <br /> extent that these soils become wet or unstable. <br /> ■ The contractor should cover all soil stockpiles that will be used as structural fill with plastic sheeting. <br /> • Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced <br /> with the existing asphalt or working pad materials not susceptible to wet weather disturbance. <br /> • Construction activities should be scheduled so that the length c time that soils are left exposed to <br /> moisture is reduced to the extent practical. <br /> Routing of equipment on the on-site fill and existing native subgrade :,ails during the wet weather months <br /> will be difficult and the subgrade will likely become highly disturbed and rutted. In addition, a significant <br /> amount of mud can be produced by routing equipment directly on the c,n-site soils in wet weather. <br /> Therefore, to protect the subgrade soils and to provide an adequate wet weai.''iler working surface for the <br /> contractor's equipment and labor, we recommend that the contractor protect expccsed subgrade soils with <br /> sand and gravel, crushed gravel, or ATB. <br /> 4.7.4.Utility Trenches <br /> Trench excavation, pipe bedding, and trench hackfilling should be r: ,lnpleted using the general procedures <br /> described in the 2020 WSDOT Standard Spec: I ications or other suitaul: procedures required by the City of <br /> Everett or specified by the pi.,;;:c, civil engineer.The native glacial deposit , mnd fill soils encountered at the <br /> site are generally of lour; ,..)n osivity o ed on our experience in tn. Puget Sound area. <br /> Utility trench backfill should consist ,i structural fill and should be placed in loose lifts not exceeding <br /> 12 inches in thickness when ,ing h i ;y (, impaction eiluipment and not more than 6 inches when using <br /> hand operr,. l n ii ai .tinn equipine ulsuch Pi, ,idequat,.: compaction can be achieved throughout the lift. <br /> Each lift, be compacl.cd prior to placing the suL,e(i!.lent lift. Prior to compaction,the backfill should be <br /> moisture : .nditioned to wits, l '' percei t if the optimum moisture content, if necessary.The backfill should <br /> be compact 1 in accordance void the cnl , is discussed above. Figure 4 illustrates recommended trench <br /> compaction cri :)ria under pavement and non ,!ructural areas. <br /> 4.7.5.Sedimentation and Erosion Control <br /> In our opinion,the erosion potential of the on-site soils is low to moderate. Construction activities including <br /> stripping and grading will exp., ;oils to the erosional effects of wind and water.The amount and potential <br /> impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather <br /> construction will increase the amount and extent of erosion and potential sedimentation. <br /> Erosion and sedimentation control measures may be implemented by using a combination of interceptor <br /> swales, straw bale barriers, silt fences and straw mulch for temporary erosion protection of exposed soils. <br /> All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion. <br /> Erosion and sedimentation control measures should be installed and maintained in accordance with the <br /> requirements of the City of Everett. <br /> GEOENGINEERS December 6,2021 Page 11 <br /> File No.24459-003-00 <br />