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1 Consent Decree Exhibit C difficult to integrate with development, as it requires excavation into the refuse and a continuous geomembrane. The requirement for the area -wide landfill gas collection system to continuously operate with a vacuum with its perforated pipes buried in refuse increases its risk of causing a subsurface landfill fire. This risk is mitigated through regular monitoring and adjustment in accordance with the operations and maintenance manual. The proposed gas cleanup action with phased active landfill gas controls also operates with a continuous vacuum but its perforated pipes are located above the refuse and are therefore less likely to cause a subsurface landfill fire. Each alternative is effective in the short-term as their technology options are put in place concurrently with development. Short-term exposure to landfill gas during construction will be controlled through the use of contractor health and safety plans. The area -wide landfill gas collection system creates the greatest short-term exposure because it requires exposure of substantial amounts of refuse. Each alternative provides permanent reduction in the mobility of landfill gas by restricting its movement into future development buildings and associated infrastructure. The proposed cleanup action and the alternative with an area -wide landfill gas collection system are more effective at this as they maintain a vacuum beneath buildings and around associated infrastructure. If collected landfill gas is treated with a flare, the proposed cleanup action and the alternative with an area -wide bndfill gas collection system will permanently reduce the toxicity and volume of landfill gas by combusting organic pollutants and oxidizing hydrogen sulfide. New pollutants that are the by-product of combustion would be created, such as carbon monoxide, sulfur dioxide and nitrogen oxides, but they would have to meet PSCAA emission limits. Hydrogen sulfide removal treatment would remove that pollutant if used. Each of these alternatives can be implemented. The technology options of the contingent active venting alternatives are integrated and implemented concurrently with phased development and are independent systems not relying on integration with previous development control systems. The proposed cleanup action is also implemented concurrently with phased development and requires only integration with any pre-existing header pipe systems. The area -wide landfill gas collection system would be more difficult to integrate and implement with subsequent development phases because the area -wide landfill gas collection system would be installed prior to development and construction activities would have to avoid disturbing the continuous geomembrane and other landfill gas control elements. The cost for the contingent active venting alternatives are similar, 'differing only in the cost of providing contingent active controls for pavement and open space areas. The alternative with contingent active venting only for buildings is estimated to cost $9.6 million. The alternative with contingent active venting for all areas is estimated to cost $11.2 million. The proposed phased active landfill gas control system is estimated to cost $8.4 million, less than either contingent active venting alternatives primarily because less pipe and gravel are required when compared to a passive system. The cost estimate for the area -wide landfill gas collection system is approximately $16.2 million, more than the proposed cleanup action (phased active landfill gas controls) because of substantial earthwork requirements and a continuous geomembrane over the Site. FINAL - March 2001 7-2 Everett Landfill Tire Fire Site Cleanup Action Plan 1 11 LJ 1 1 1 1 1 1 II 1 1 11 1 1