9 9 CITY OF EVERETT PARCEL 2023-12-27

Landau Associates Standards for Construction and Maintenance of Wells (WAC Chapter 173-160).The replacement well will be constructed with a 6-inch casing and 4 ft of wire-wrapped stainless-steel screen (0.030-inch slot size). The total depth of the completed well will be approximately 32 ft bgs, but the final depth will be determined in the field. A filter pack consisting of 10-20 Colorado Sand (or similar) will extend to approximately 2-3 ft above the top of the screen. The proposed design of EGW192R is presented on Figure 3. Before vault and wellhead equipment installation, the new extraction well will be developed using a centrifugal pump to remove sediment and silt from the casing. The new extraction well will be equipped with a multi-stage submersible extraction pump (i.e., Grundfos 16S model [or similar] with variable frequency drive [VFD] and environmental retrofit, and shroud) appropriately sized to transfer groundwater at the design flow rate from the well, through the conveyance piping system, to the groundwater treatment system. Based on groundwater modeling results using the proposed location of EGW192R and available head calculations, the estimated extraction rate at EGW192R is 20 gpm. The estimated capture zone for EGW192R, operating at 20 gpm, is presented on Figure 4. Initial operation of the new well will be based on achieving the design drawdown necessary to hydraulic capture and containment of the plume near the PMC. The actual flow rate will likely vary from the estimated extraction rate and will be determined during well startup and testing. Drawdown will be monitored continuously in extraction well EGW192R using a pressure transducer and quarterly at nearby monitoring wells and piezometers using manual gauging methods. The drawdown will be adjusted as necessary to achieve the Phase 2 IAO. Discharge of treated groundwater from the GET system into PMC is authorized by NPDES Permit WA0991001. The permit allows for a maximum discharge flow limit of 250 gpm to Powder Mill Creek and provides specific chemical concentration discharge limits. Based on the design flow rates of EGW192R (in place of the flow from EGW192) and the treatment capacity of the current GET system, the permitted limit flow and discharge limits will not be exceeded. Conveyance Piping to Treatment System The extraction pump at EGW192R will be attached to a 2-inch stainless-steel rise pipe that transitions in the well vault to plastic conveyance piping. Conveyance piping within the vault will consist of 2-inch high-density polyethylene (HDPE) piping (SDR 11). Straight pipe sections will be connected via butt- welded (fusion welded)joints, as needed. Other connections will be made with factory-molded HDPE fittings. Pipe selection and design are based on head loss calculations, an external pressure/loading evaluation, and a comparison of internal pressures to manufacturers' pipe specifications. The conveyance piping to the treatment system in the Phase 2 area will be adjusted to connect to new extraction well EGW192R. The piping from EGW192R will be connected to the conveyance piping lateral from EGW176 with a Wye fitting (which then joins the primary Phase 2 force main to the treatment system). EGW192 Relocation Work Plan Powder Mill Gulch—Boeing Everett Plant 5 October 1, 2020