10312 EVERGREEN WAY SONIC Geotech Report 2023-05-25

Geotechnical Engineering Report 11 January 8,2021 Glint Car Wash and Sonic Everett,Everett,Washington RG1 Project No.2020-643-1 building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE Perimeter foundation drains, details shown on Figure 4, are generally installed around the building. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. If the building is supported on reinforced slab with thicken edge and paved to the building, the footing drains can be eliminated. 5.6.3 INFILTRATION RGI has reviewed the onsite soil conditions for the potential for infiltration.The native soil is glacial till, which is not efficient for onsite infiltration systems and the groundwater is very shallow. If an infiltration system has to be used, RGI recommends that bioswale or rain garden be considered and the system must have an overflow system. For preliminary system design, RG recommends that an allowable infiltration rate of 0.1 inch per hour be used for system design. An overflow system is recommended if infiltration system will be used. The infiltration can only be used in the area that the soil has not be treated. If the onsite soil is be treated with Portland cement, infiltration system cannot be used anymore. 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, bedding and backfill should be completed in accordance with City of Everett specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil's maximum density as determined by ASTM D1557. The native soils may be used as backfill provided they can be adequately moisture conditioned and compacted in dry weather condition. Imported structural fill may be required for trench backfill in winter. 5.8 PAVEMENTS Pavement subgrades should be prepared as described in Section 5.2 of this GER and as discussed below. Regardless of the relative compaction achieved, the subgrade must be Corporate Office 17522 Bothell Way Northeast Bothell,Washington 98011 Phone 425.415.0551• Fax 425.415.0311 WNW.riley-group.com