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f 1 1 The City of Everett The Floyd & Snider Team Everett Landfill/Tire Fire Site 2.2.1 CLEANUP ACTIONS FOR EXISTING CONDITIONS The completed interim actions for control of groundwater, direct contact and surface water pathways included construction of the leachate collection and transmission system, geomembrane cover on the eastern side slopes of the landfill to control leachate seeps, site fencing, site cover, control of surface water, removal off -site of remaining tires, and on -site disposal and capping of tire fire ash. These actions were effective in controlling these exposure pathways and fulfilled the most significant needs for physical cleanup actions relative to existing site conditions. The BFS proposes compliance monitoring requirements for groundwater to ensure continued compliance. In addition, cleanup actions and compliance monitoring programs to address existing conditions for stormwater/sediment runoff and for landfill gas are recommended in the BFS. Recommended cleanup actions for landfill gas includes gas control measures for existing on - site facilities, perimeter monitoring and contingent installation of perimeter landfill gas migration controls. Institutional controls are also proposed in the BFS for the site relative to all pathways of concern. 2.2.2 CLEANUP ACTIONS FOR FUTURE CONDITIONS Potential future development, consistent with the Everett Comprehensive Plan, will alter the existing conditions of the site by constructing infrastructure components, buildings, and landscaped areas. The property may be transferred to other owners. Public access will be increased, and construction disruption of the clean soil cap will be necessary. Within each pathway, remedial alternatives are recommended which address environmental requirements under MTCA for any potential future site development. The recommended alternative for landfill gas management controls for future developed conditions involves installing a vacuum extraction system as development occurs. The system would be comprised of perforated, horizontal extraction pipes placed above the refuse, one or more blower locations, vent pipes and options for treatment of releases. Vacuum extraction pipes would be embedded within gravel -filled trenches above the solid waste and generally covered with a barrier layer to reduce atmospheric intrusion. The system has the ability to tie in with perimeter migration control wells if necessary. Special consideration would be given to the conditions at the boundary between developed and undeveloped areas that would be created when a portion of the site is developed. Additionally, the phased active system would eventually be needed to operate effectively as a passive gas venting system as landfill gas generation slows over time. Passive controls, including booting and sealing requirements, are included for such features as light poles and fence posts. Buildings and temporary enclosures would be fitted with full-time sensors and automated alarms. Human health and the environment would thus be protected by the phased active gas management system and concurrent institutional controls and compliance monitoring. The recommended alternative for the groundwater pathway includes continued operation of the leachate collection system, installation of a hydraulic barrier beneath landscaped areas to reduce leachate generation, and implementation of stormwater management system restrictions to minimize stormwater infiltration. docs\C mpliance Mo Everett Lan\CMCPF maker- final Compliance Monitoring and Contingency Plan docslCompliance Monitoring PIan�CMCP 11-10-OO.doc FINAL - March 2001 Page 2-3