4937 EVERGREEN WAY QFC FUELING STATION Geotech Report 2023-02-17

Geotechnical Engineering Report 5 January 7,2020 QFC 852 Fuel Station,Everett,Washington RGI Project No.2019-258A ➢ Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather ➢ Directing runoff away from exposed soils and slopes ➢ Decreasing runoff velocities with check dams, straw bales or coir wattles ➢ Confining sediment to the project site ➢ Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consisted of medium dense to very dense silty sand with trace gravel and sand with varying amounts of silt and gravel. Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1.5:1 (Horizontal:Vertical). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring support su ort the excavations should be considered. For open cuts at the site, RGI p recommends: ➢ No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least 5 feet from the top of the cut. ➢ Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting. ➢ Construction activities are scheduled so that the length of time the temporary cut is left open is minimized. ➢ Surface water is diverted away from the excavation. ➢ The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures. In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor 1 I- RILEYGROUP