2725 32ND AVE NE 2018-01-02 MF Import

t WEYERNAFUSEN SMITH ISLAND LANDFILL RS AND NF DIES OUTFALL006 ELIMINATION Outfall 005 Elimination NPDES Permit No. WA-003197-6 (September 2003) authorizes Weyerhaeuser to discharge storm water and landfill leachate from two outfalls (Outfall 001 and 005). These outfalls discharge into Steamboat Slough and Snohomish River, respectively. Surface water runoff from areas around the landfill, including the adjacent log sort yard, collect in a perimeter ditch that drains to Outfall 005. Outfall 005 then discharges this runoff directly into the Snohomish River. Outfall 001 discharges runoff water that collects in the onsite wastewater treatment system (formerAY " used to treat pulp mill effluent) into Steamboat Slough. As a condition of the NPDES permit, Weyerhaeuser will eliminate Outfall 005. All runoff within the landfill perimeter ditch will be transferred into the onsite wastewater treatment system and then discharge through Outfall 001. The onsite wastewater treatment system consists of a primary settling basin, secondary stabilization (biological treatment) basin, and secondary settling basin (see Figure 2). The original treatment system commonly handled 23 mgd (-70 ac-ft) of industrial wastewater from the former Weyerhaeuser pulp and paper mill. Suspended solids are settled out in the quiescent zone of the primary settling basin. Nutrients are biologically degraded in the secondary pond where floating aerators can be placed into service, as needed. Secondary (biological) solids are settled in the secondary settling basin. Outfall 001's gate control structure discharges effluent from the secondary settling basin into Steamboat Slough. Weyerhaeuser will construct a stormwater lift station to handle the runoff from the area surrounding the landfill and the log sort yard south of the landfills. The stormwater lift station will redirect existing stormwater flows to discharge through Outfall 001. Outfall 005 will be plugged to eliminate the discharge into Snohomish River. The stormwater lift station will be a duplex submersible pump station installed inside a 6-foot diameter concrete "manhole" wet well. The wet well will receive gravity flows from surface drainage ditch. The total pumping capacity will be sized to handle the projected combined 24-hour storm runoff volume for the 6-month storm event (0.84 acre-feet) from the drainage area. Runoff in excess of this amount will be temporarily stored in the drainage ditch, which has an estimated storage volume of 8.2 acre-feet, until it can be pumped out. The proposed location of the sump pump and a cross section of the storrn•.vater lift station are shown in Figure 5.