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Consent Decree Exhibit C There are no known or anticipated public concerns that the alternatives under consideration do not address. If flare treatment were used as appropriate, consideration would have to be given to noise and vibration concerns. The proposed cleanup action for the gas pathway thus meets all the criteria to be considered "permanent to the maximum extent practicable". The alternatives that rely on contingent active venting are rejected because they maintain a vacuum beneath buildings, pavement and open space and because they were estimated to cost $1.2 to $2.8 million dollars more than the proposed cleanup action. The area -wide landfill gas collection system was rejected because it does not provide added benefit for the additional cost and short-term risks that would be incurred. 7.2.2 Provide for a Reasonable Restoration Time Frame Each of the four alternatives provides reasonable restoration time frame. They are constructed prior to or concurrently with development. 7.2.3 Consider Public Concerns Raised during Public Comment on the Draft Cleanup Action Plan Public concerns are unknown at this time. The public has not had an opportunity to comment on the draft cleanup action plan as of this date. Evaluation of the alternatives against this criterion can be done after such comments are received. 7.3 CLEANUP ACTION ALTERNATIVES FOR GROUNDWATER In addition to the proposed cleanup action for groundwater, which includes a hydraulic barrier, stormwater management restrictions and zoned pile installation restrictions, the following alternatives were evaluated: t • Hydraulic barrier and stormwater management restrictions Y 9 • Excavate and remove landfilled materials 7.4 JUSTIFICATION OF PROPOSED CLEANUP ACTION FOR GROUNDWATER 7.4.1 Permanent Solutions to the Maximum Extent Practicable A hydraulic barrier under landscaping (except in areas of steep slopes), in conjunction with pavements and buildings, will result in about 90 percent of the surface area having relatively low impervious surfaces. This barrier will reduce leachate generation by reducing potential recharge to the shallow groundwater system through rainfall or irrigation water input. Stormwater management restrictions that minimize the infiltration of collected stormwater will reduce leachate generation. Reduction in leachate head in the shallow aquifer will increase the potential for upward groundwater gradients at the Site, and reduce the potential for downward migration of leachate contaminants to the lower aquifer. FINAL - March 2001 7-3 Everett Landfill Tire Fire Site Cleanup Action Plan 1