11625 AIRPORT RD SONRISE CHRISTIAN CENTER Geotech Report 2022-10-25

I I GEOTECHNICAL EVALUATION EVERETT,WASHINGTON February 6,2018 If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation,to verify the suitability of the proposed systems. 8.1.3 Erosion and Sediment Control Erosion and sediment control(ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils,to take place during the dry season(generally May through September). However,provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season(generally October through April). • All site work should be completed and stabilized as quickly as possible. • Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size(AOS),construction of a berm,or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. 8.1.4 Stormwater Management Due to the presence of very shallow groundwater, low soil permeability, and a shallow depth to a restrictive layer, infiltration of runoff is not feasible. We anticipate that one or more below-grade detention vaults will be required for storage and flow control. If concrete vaults are proposed,the following wall design criteria may be used. Additionally,an allowable soil bearing pressure of 4,o0o pounds per square foot (psf) may be used for foundation design, if applicable. The following table, titled Wall Design Criteria, presents the recommended soil related design parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system is used. I PO Box 82243 5 Kenmore,WA 98028 (206)331-1097 Cobaltgeo(a>gmail.com