9 9 CITY OF EVERETT PARCEL 2023-12-27

Landau Associates treated groundwater piping and a new outfall into Powder Mill Creek north of the extraction wells (discharge authorized under a National Pollutant Discharge Elimination System [NPDES] permit).The Phase 2 portion of the system was connected to the Phase 1 system through piping and conduit that was installed beneath Seaway Boulevard. The Phase 2 GET system began operating in September 2015. In late 2015/early 2016, the Phase 1 portion of the GET system was expanded to include two additional extraction wells on Boeing property.These Phase 1 expansion extraction wells began operating in February 2016. EGW192 Well Screen and Pump Biofouling Each of the extraction wells associated with the GET system have generally run fairly consistently, and the incidence of observed biofouling or mineral fouling in the wells and in the treatment system have been negligible. However, during routine maintenance at EGW192 in late 2017 related to a steady decrease in flow rates in the well (to below 2 gallons per minute [gpm] as compared to the initial pumping rates of over 3.5 gpm), highly turbid water with the appearance of organic biological growth was observed in water purged/pumped and collected directly from the extraction well. The well pump was subsequently cleaned and the well redeveloped to remove the turbidity. However, within 6 months of the redevelopment activities, the pumping rate from the extraction well decreased to below rates measurable by the flow meter. In late 2018, the well was rehabilitated using an acid washing procedure and the pump was replaced. This process temporarily restored the pumping rates to acceptable levels (around 2.5 gpm), but the rates again declined over the course of approximately 9 months reducing to levels below 0.5 gpm and resulted in a loss of ability to maintain the desired aquifer drawdown in this area. In late 2019, the well was again rehabilitated with the acid washing procedure, again restoring pumping rates; however, pumping rates declined to minimal values in less than 6 months. EGW192 was rehabilitated once more in May 2020 resulting in similar restored pumping rates but quickly followed by rapidly declining pumping rates. The observed period of fouling resulting in quickly decreasing pumping rates appears to be getting more frequent and has reached a level of unsustainable operation and maintenance. The aquifer thickness at the location of this well is very thin (8-9 feet [ft] of saturated thickness above the underlying silt interbed), which is why the initial pumping rates at EGW192 were relatively low to begin with in comparison to other Phase 2 area extraction wells (some with pumping rates over 20 gpm). EGW192 is the only well of the 12 GET system extraction wells where such fouling has been observed. It is likely that the fouling is the result of unique Site conditions at this well location. More specifically, it is likely the result of combination of the following factors: EGW192 Relocation Work Plan Powder Mill Gulch—Boeing Everett Plant 2 October 1, 2020