9 9 CITY OF EVERETT PARCEL 2023-12-27

Landau Associates is anticipated that the well will be backfilled with bentonite grout or chips in accordance with WAC 173-360-410(2)(a), but the final method of decommissioning will be selected in consultation with the driller. The associated vault and wellhead equipment will be reused, if possible, during the construction of replacement well EGW192R. Any equipment from existing well EGW192 not utilized during construction of the replacement well will be decontaminated and stored for future reuse or disposed of, as appropriate. Replacement Well Location The Phase 2 area of the GET system currently consists of seven groundwater extraction wells, which are operated to achieve the Phase 2 IAO described above. The number of wells, well locations, and screen locations of the extraction wells were originally established using groundwater modeling, as described in the Phase 2 IA Conceptual Design Report (LAI 2012).The seven wells are located on City property (Lot 9) north of Seaway Boulevard, generally along a north-south oriented access road that runs roughly parallel with PMC. The extraction wells are screened within the upper and lower Esperance Sand aquifer units as modeled. Existing well EGW192, as previously described, is located where there is minimal saturated thickness above the silt aquitard.This well was drilled and screened approximately 3 ft into the aquitard to provide a "sump" that allows for sufficient hydraulic head above the pump intake even when groundwater is drawn down to near the top of the aquitard. Replacement extraction well EGW192R will be located to the southwest of existing well EGW192 (Figure 2) in an area of the hillside on an old logging road where the aquifer has a larger saturated thickness and is not within the wetland area along PMC.The new location was selected in order to minimize the potential impacts of biofouling on the operation and maintenance of EGW192R and still achieve the Phase 2 IAO. Replacement Well Installation and Design The boring for EGW192R will be drilled using hollow-stem auger(HSA) or rotosonic methods by a professional driller licensed in the State of Washington. During drilling, core samples will be collected and logged across the depth of the soil boring to classify soil lithology in accordance with the Unified Soil Classification System (USCS). Soil samples will be collected using a 3.25-inch-diameter Dames and Moore sampling device (or similar). The total depth of the boring will be approximately 32 ft bgs, but the final depth will be determined in the field to ensure that the bottom of the boring extends to the top of the silt interbed but does extend into or through it. Similar to existing Phase 2 extraction wells, replacement well EGW192R will be constructed with carbon steel casing and stainless-steel screened sections and in accordance with the Water Well Construction Act of 1971 (Revised Code of Washington [RCW] Chapter 18.104) and the state Minimum EGW192 Relocation Work Plan Powder Mill Gulch—Boeing Everett Plant 4 October 1, 2020