501 RIVERSIDE RD REGIONAL DISPOSAL COMPANY EVT TRANSFER FACILITY PHASE 1 SITE IMP 2025-07-28

1 II. PRELIMINARY CONDITIONS SUMMARY Existing Conditions The project site consists mainly of asphalt, cement concrete, and gravel with some small areas of ' grass and brush. There are currently four structures on the site. Snohomish County maintains a modular office building at the northwest corner of the site. To the south of the modular building ' is an open-sided, covered equipment storage structure that is a legacy structure of the Weyerhaeuser use of the site. To the east of this structure is a small temporary office building used by RDC to manage the operations on the site. To the south of the RDC office building is another open-sided equipment maintenance structure used for fueling and maintenance of site equipment. Rail to the site is provided by a private spur from the BNSF mainline facilities to the west. The spur splits into two parallel tracks as it enters the property,both of which continue to the north boundary of the site. ' On-site soils consist primarilyof fill material overlying younger alluvial and estuarine deposits. Y gY g p The fill layer varies from 3 to 71/2 feet deep. The fill generally consists of medium dense to dense sand with gravel and silt. The project geotechnical report (included in Appendix A) indicates groundwater seepage was observed to range from 11 to 14 feet below the ground surface during site boring, and it is expected that the groundwater levels will fluctuate in response to water ' levels in the Snohomish River. The site is flat with slopes generally less than 0.5 percent. Stormwater on the site drains from north to south through a system of catchbasins and pipes and then to the east where it outfalls to the Snohomish River. Drainage flowing onto the site from the BNSF railroad property to the west appears to be intercepted by an open ended pipe and by a catch basin at the south end of the ' site. Operations at the site are subject to the requirements of an NPDES Industrial Stormwater ' General Permit. Water quality discharges from the site are monitored at a manhole near the southeast corner of the site. The site has incurred violations of turbidity water quality standards for the past three years. ' Developed Conditions ' The proposed Phase 1 site improvements include overlay of the existing asphalt adjacent to the eastern railroad track. The pavement overlay will consist of geogrid over the existing surface, a 12-inch crushed surfacing base course section, and 71/4 inches of hot mix asphalt. A new ' stormwater conveyance system will also be installed for the Phase 1 area. The pavement overlay area will be constructed as a shed slope allowing storm runoff to sheet flow to a slotted drain at the west edge of pavement. The slotted drain will convey stormwater from north to south where it will be tied into the existing drainage system. The existing catchbasins and 12"concrete pipes south of the pavement overlay area will be replaced with new catchbasins and 18"ductile iron ' Regional Disposal Company June 11, 2014 Everett Transfer Facility Reid iddleton Stormwater Site Plan -4 - I