3800 RIVERFRONT BLVD 2025-07-23 - Laserfiche WebLink

1 Consent Decree Exhibit C Given site conditions, the alternative with unrestricted pile construction will not likely degrade lower aquifer quality. However, the proposed cleanup action for groundwater increases the certainty of this conclusion by providing for protection of the deep aquifer in those areas where it is hypothetically most vulnerable - where the shallow aquifer has contaminant concentrations that, if connected to the deeper aquifer, could cause exceedances of cleanup levels at the point of compliance. It also allows flexibility for development in those areas where the shallow aquifer is not significantly impacted or the aquitard is absent. The area of the landfill that is underlain by aquitard will be sampled to obtain a statistically relevant set of characterization data. If data shows that areas of the landfill contain contaminant concentrations in leachate that could, if connected to the lower aquifer, cause an exceedance of cleanup levels at the point of compliance, pile installation within that zone will be restricted to augercast piling. Drilled augercast piles will have no negative impact on the hydraulic properties of the aquitard since concrete is placed under head as the auger is removed maintaining a strong hydraulic seal at the aquitard. Pile installation restrictions will not be necessary in the western portions of the Site where the aquitard is not present. Comprehensive compliance monitoring will be approved and initiated prior to pile installation. Contingency plan measures are focused on further reducing leachate quantity in the shallow aquifer if lower aquifer quality is determined to be at risk based on compliance monitoring results. Through these methods, the proposed cleanup action for groundwater under future conditions increases the certainty of groundwater pathway protectiveness. It meets the cleanup standards and is protective of human health and the environment. The proposed cleanup action for groundwater provides long-term effectiveness through providing measures that increase the certainty of groundwater pathway protectiveness and commitment to compliance monitoring and contingency measures. The proposed cleanup action for groundwater is effective in the short-term because the groundwater pathway is in compliance with cleanup standards under existing conditions. Effectiveness of the groundwater pathway alternatives for future conditions is relevant only to increasing the certainty of protectiveness in the long-term. The proposed cleanup action for groundwater is likely to provide a permanent reduction in the volume and mobility of leachate in the groundwater system due to anticipated reduction in leachate quantity and associated leachate head in the shallow aquifer. The proposed cleanup action for groundwater will not reduce the toxicity of leachate. Therefore, continued operation of the leachate collection system is required unless it can be shown that shallow aquifer groundwater has attained compliance with cleanup standards. The proposed cleanup action can be implemented using common design, permitting, construction and monitoring practices. Costs associated with the proposed cleanup action for groundwater above the "base case" costs for hydraulic barrier and stormwater management restrictions include the increased cost of using augercast piling in restricted areas. For the purposes of this evaluation, it is assumed buildings will cover about 14 acres of the Site and that one quarter of the building square footage will have the zoned designation requiring augercast piles. The estimated cost was developed using only the differential cost between steel piles (estimated to be the lowest cost FINAL - March 2001 7-4 Everett Landfill Tire Fire Site Cleanup Action Plan 1