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0 5.2 Vadose ZoneMitigation In accordance with 27CCR, Sections 20925, a network of soil -pore gas monitoring probes have been constructed around the perimeter of the WMUs and are regularly monitored to verify the adequacy of the gas control measures. If methane concentrations exceed the regulatory limit (5%), the existing LFG collection well system at the site will be expanded to minimize the potential for gas migration and impacts to the vadose zone and groundwater. In addition, liner construction will be completed in accordance with a construction quality assurance (CQA) plan that will minimize liner defects and, thus, minimize the potential for leachate to migrate to the vadose zone. 5.3 Mitigation of Groundwater impacts In the event that groundwater is impacted by landfill constituents, a number of remedial responses could be implemented, depending on the nature, location, and concentration of the waste constituents detected in groundwater. These remediation systems could include ex -situ "pump and treat" methods (such as currently in place), or in-situ treatment of impacted groundwater. If it is determined that impacts are related to landfill gas migration, additional landfill gas collection wells may also be installed. Should a new release or increasing VOC concentrations be identified, it may necessitate expanding or modifying the existing CAP/monitoring well array located downgradient of the Austin Unit. Such an expansion/modification could include construction of up to two new groundwater extraction wells and 10 LFG extraction wells for containment of the release. In order to improve the effectiveness and efficiency of the existing CAP, Forward Inc. is currently in the process of expanding the existing CAP including the construction of an additional groundwater extraction well at the northwest corner of the Austin Unit (near AMW-1), and construction of a second air stripper and infiltration basin. Since these additional CAP costs are included in the existing CAP budget, the estimated groundwater mitigation costs summarized in Table 1 only include the installation of one groundwater extraction well. With the exception of associated energy costs for operation of the extraction well, no additional reporting, analytical costs, or operation and maintenance costs are anticipated for the expansion/modification of the CAP since these costs would be integrated into the existing CAP budget. In accordance with 27CCR, Section 20380(b), Forward Landfill must establish and maintain assurance of financial responsibility for initiating and completing corrective action for all known or reasonably foreseeable releases from the facility. Recognizing the landfill continues to generate LFG, it is expected that the worst-case release from the facility would be a gas -related release to groundwater. Given this type of release, remedial efforts would most likely involve making adjustments to and/or expanding the existing LFG system, and enhancement to the existing pump D:\2014-0012\FA finassur.dou 8 3/10/2014, Rev. 0