3815_PGSF WMVD Pkg 2_Vol 4-2_03.03.2026_BXWA_Certified

ASPECT CONSULTING PROJECT NO. AS190583A-08  MAY 21, 2025 FINAL ES-3 Because Upland Area groundwater is not considered a potential source of drinking water, the potentially complete exposure pathway for Upland Area groundwater to impact human health and the environment is discharge of contaminated groundwater to sediment and surface water of the East Waterway. While there are groundwater metals exceedances in Upland Area shoreline wells, the empirical data from intertidal porewater and seep sampling, most accurately representing groundwater at the point of discharge, indicates that dissolved metals in groundwater do not pose a risk to the East Waterway. Similarly, there are inconsistent, localized, and sporadic groundwater cleanup level exceedances of TPH and polycyclic aromatic hydrocarbons (PAHs) in monitoring wells across the Upland Area but no exceedances in shoreline groundwater or seeps. Concentrations of un-ionized ammonia above the PCL are present in shoreline groundwater in the northern portion of the Upland Area. NH3 concentrations were less than the PCL at the six intertidal seep locations sampled, and at the three surface water locations sampled immediately offshore of the Log Pond Area, consistent with those waters being exposed to the atmosphere and thus oxygenated. Feasibility Study The FS is used to develop an appropriate final cleanup action for the Upland Area, based on evaluation of a range of cleanup alternatives identified as applicable and technically feasible approaches to achieve the applicable MTCA-required cleanup standards, taking into account the effect of the prior interim actions. The FS follows a streamlined approach in accordance with WAC 173-340-360(3)(d) and identifies a preferred Cleanup Alternative that includes the completed interim actions plus targeted new components, including contingent cleanup actions. The preferred Cleanup Alternative consists of the following:  The remedial actions already completed, and the 7.6 acres of cap remaining to be installed as originally described in the second amendment to the Agreed Order  Capping of the City’s Utility Property  Long-term groundwater compliance monitoring in accordance with a Groundwater Compliance Monitoring Plan approved by Ecology  Long-term inspection and maintenance of the Upland Area environmental cap in accordance with a Cap Inspection and Maintenance Plan approved by Ecology  Institutional controls to be articulated in an environmental covenant filed with Snohomish County, which includes preparation of a Soil and Groundwater Management Plan approved by Ecology  Financial assurances Depending on the Port’s future use of the warehouse, the preferred Cleanup Alternative also includes two contingent cleanup actions:  If the warehouse is converted to commercial use, construction of a passive vapor barrier across the building’s entire first floor; or