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1 <br />Consent Decree Exhibit C <br />Justification for cleanup action selection for each environmental exposure pathway is organized <br />by the three criteria from WAC 173-340-360(3) and presented in the following sections. <br />5.1 CLEANUP ACTION ALTERNATIVES FOR GAS <br />In addition to the proposed cleanup action, which includes existing building controls, perimeter <br />compliance monitoring and contingent installation of perimeter landfill gas migration controls, <br />the following alternatives were evaluated: <br />• Existing building controls, perimeter compliance monitoring and immediate <br />installation of perimeter landfill gas migration controls <br />• Excavation and removal of landfilled materials <br />5.2 JUSTIFICATION OF PROPOSED CLEANUP ACTION FOR GAS <br />5.2.1 Permanent Solutions to the Maximum Extent Practicable <br />The proposed gas cleanup action provides overall protection to human health and the <br />environment. The Animal Shelter and Transfer Station are protected through appropriate <br />mitigation measures, compliance monitoring and contingency plans. Compliance monitoring is <br />implemented for perimeter subsurface migration as soon as possible. A perimeter landfill gas <br />migration control system will be installed if subsurface landfill gas migration past the Site <br />boundary is confirmed by compliance monitoring conducted in accordance with the approved <br />CMCP. <br />The proposed cleanup action provides long-term effectiveness against subsurface landfill gas <br />migration. Compliance monitoring would be implemented immediately. Perimeter landfill gas <br />migration controls will be installed if compliance monitoring demonstrates it is necessary. The <br />magnitude of residual risk with this alternative is minimal since landfill gas ambient emissions do <br />not exceed MTCA cleanup standards and do not present an explosive risk. This alternative also <br />includes corrective actions, compliance monitoring and contingency plans for the Animal <br />Shelter, Transfer Station, and off -site buildings. <br />The proposed cleanup action for gas has acceptable short-term risks from construction and <br />implementation. Exposure is limited to construction of the landfill gas probes, the perimeter <br />landfill gas controls if constructed, and implementing corrective actions at the Animal Shelter <br />and Transfer Station. Worker health and safety plans will be implemented to reduce the risk <br />during construction. <br />The proposed cleanup action for gas achieves a permanent reduction in landfill gas mobility by <br />reducing its ability to migrate into the Animal Shelter, Transfer Station, and off -site buildings. It <br />will demonstrate that landfill gas is not migrating beyond the Site boundary, or it will achieve <br />permanent reduction in subsurface landfill gas migration through the construction of perimeter <br />landfill gas controls, if landfill gas is confirmed above the compliance levels per the CMCP. The <br />contribution from landfill gas toxics to ambient air does not exceed MTCA cleanup standards, <br />and human health and the environment are not affected. <br />FINAL - March 2001 5-2 Everett Landfill Tire Fire Site <br />Cleanup Action Plan <br />1 <br />1 <br />I <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />