9 9 CITY OF EVERETT PARCEL 2023-12-27

Landau Associates • The shallow nature of the well (the water table is only 5—6 ft below ground surface [bgs]) and the saturated zone at this location is also relatively thin as noted above; • The proximity of the well to overlying wetlands that are rich with organic materials and likely high in microbial activity, which may be getting pulled into the EGW192 well screen; and • The location of the well screen, which is set in alluvial creek deposits of Powder Mill Creek and likely in greater communication with infiltrating precipitation and other surface water in the area (that, again, are likely to be higher in organic materials and biological activity). Based on the increasing frequency/severity of fouling and the likely conditions leading to the fouling described above, at Boeing's request, Ecology agreed to allow Boeing to relocate EGW192 to a location with less potential to suffer from biofouling (Ecology 2020). Specifically, Ecology (conceptually) approved Boeing's request to replace EGW192 with another extraction well located farther west or southwest from the current location of EGW192 where the aquifer thickness would be greater, it would be farther removed from the wetland, and it may be installed in the Esperance Sand formation rather than the creek alluvium.This relocation of the well should allow for higher pumping rates, greater drawdown/groundwater capture, and reduced potential for well fouling. Extraction Well Replacement The following sections describe activities pertaining to replacement of EGW192 with a new extraction well (to be designated as "EGW19211"), which consists of the following activities: • Decommissioning of extraction well EGW192 (and removal of associated vault and wellhead equipment); • Installation of extraction well EGW192R (and associated vault and wellhead equipment) southwest of the current location of EGW192; • Installation of additional/replacement piping for conveyance of extracted groundwater from EGW192R to the treatment system; and • Installation of additional/replacement conduit and cable for electrical lines and communications line for operation and control of the extraction well. This work plan provides details of the extraction well relocation, design, construction, and startup. Design drawings for EGW192R and associated equipment and infrastructure are included as Attachment 1 to this report. Design details of the original GET system are provided in the Phase 1 IA work plan (LAI 2011) and Phase 2 IA work plan (LAI 2013), including process flow diagrams, design calculations, and detailed plans and specifications. Existing Well Decommissioning Existing well EGW192 will be decommissioned by a professional driller licensed in the State of Washington. Decommissioning will be performed in accordance with the state Minimum Standards for Construction and Maintenance of Wells (Washington Administrative Code [WAC] Chapter 173-160). It EGW192 Relocation Work Plan Powder Mill Gulch—Boeing Everett Plant 3 October 1, 2020