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1 The City of Everett The Floyd & Snider Team Everett Landfill/Tire Fire Site ambient air sampling and related evaluation. An explosion and fire risk analysis was completed at the request of Ecology to evaluate the explosion and fire risk of the preferred gas management system. Landfill gas volume in 2000 was estimated to be 230 cubic feet per minute (cfm), down from 625 cfm in 1974 at time of closure. A USEPA model predicts an annual landfill gas generation reduction of approximately 7.5 cfm over the next ten years. The landfill gas evaluations conclude that emissions to ambient air do not exceed either the proposed cleanup levels or PSCAA Regulation III Acceptable Source Impact Levels (ASILs). Measurements show that landfill gas may be migrating outside property limits in some perimeter areas of the landfill. Appropriate controls may be needed to ensure that subsurface gas does not extend beyond the site boundary and to manage potential explosion risk in confined spaces. The groundwater pathway at the site includes both a shallow and a deep aquifer. Within the landfill site, the shallow aquifer contains leachate — potentially contaminated water present within the buried refuse. Leachate flows across the site, west to east, and is then collected at the eastern site boundary by a leachate collection system, installed in 1997-1998 as an interim action. The collected leachate is conveyed off -site for treatment. A post -construction evaluation of the effectiveness of the leachate collection system concludes that landfill leachate as well as shallow groundwater east of the leachate trench is being collected by the system. Compliance monitoring is proposed to ensure the continued effective operation of the leachate collection system. Based on six groundwater sampling events over the previous ten years, there have been neither significant water quality impacts to the deep aquifer that underlies the landfill site, nor impacts to the Snohomish River. Compliance monitoring is proposed to continue during future site conditions. Direct contact with buried landfilled materials and tire ash is prevented via the existing site cover of clean soil. Additionally, secured fencing surrounds the portion of the site not currently utilized by existing facilities. Isolation of landfilled materials from environmental exposure pathways with a soil cap is a proven and acceptable alternative for municipal landfill facilities. The surface water pathway could potentially carry landfill and tire ash contaminants at levels of concern to adjacent surface water drainage ditches, wetland areas, and ultimately to the Snohomish River. These surface water drainage ditches also receive runoff from upgradient industrial and residential properties, roadways and active railroad corridors. Previous studies of surface water were generally directed to assess potential tire ash runoff impacts and leachate seeps. Interim actions have address both of these concerns through leachate collection and isolation of the tire ash. Sediment samples taken in 1997 and 1999 measure concentrations of some compounds above MTCA Method A cleanup levels. However, these compounds are either not typical of landfill runoff, or were measured off -site in areas not subject to landfill runoff. 2.2 SUMMARY OF CLEAN UP ACTIONS The BFS (Floyd & Snider, 2000) separately evaluates and recommends alternatives for cleanup actions for each pathway under existing conditions and potential future developed conditions. Recommended cleanup actions are described below. dots\ jompli Oce Monitoring Everett landfil CP maker- final Compliance Monitoring and Contingency Plan dots\Compliance Monitoring Ptan\CMCP 11-10-OO.doc FINAL - March 2001 Page 2-2