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Consent Decree Exhibit C 4.2 COMPLIANCE MONITORING AND CONTINGENCY PLAN OBJECTIVES Compliance monitoring plans would be implemented for groundwater, surface water and landfill gas. See the Compliance Monitoring and Contingency Plan (CMCP) for more detail. 4.2.1 Landfill Gas Compliance Monitoring and Contingency Plan Objectives Landfill gas monitoring includes compliance monitoring at the Site boundary to ensure landfill gas does not migrate undetected past the compliance point. New compliance monitoring landfill gas probes will be installed around the Site boundary, outside the limits of buried waste, at a spacing of 200' along the western Site boundary and 100' along the northern Site boundary. They will be monitored in accordance with the approved compliance monitoring plan, which includes quarterly monitoring for flammable gas with a compliance limit of 5% methane by volume. Monitoring of the existing Animal Shelter and Transfer Station will also continue. This monitoring includes installed, continuous sensors with an action level of 1,000 ppm and periodic hand-held sensors with an action level of 100 ppm. Representative off -site buildings will continue to be monitored for a minimum of three years. If there are no confirmed landfill gas concentrations above 100 ppm during this period, then off - site monitoring will cease. If there is a confirmed landfill gas measurement exceeding 100 ppm, then monitoring will continue for another three years. Thus, three, consecutive years of undetected landfill gas measurements are required before off -site monitoring can be terminated. Off -site building monitoring would be reinstated if perimeter gas monitoring confirmed migration of subsurface gas at the Site boundary. In this case, monitoring of off -site buildings within 500 feet of the affected probes would begin and continue until the probe reading became less than 5% methane by volume. 4.2.2 Groundwater Compliance Monitoring and Contingency Plan Objectives Groundwater pathway inspection requirements for developed conditions include periodic observation of leachate collection system and monitoring well heads. The groundwater compliance monitoring plan will include additional monitoring wells located downgradient of the landfill, outside the boundary of landfilled materials, between the landfill and the point of discharge into the Snohomish River, no further than 100' east of the most easterly BNSF tracks. Area background wells will also be installed upgradient, west, of the Site. Existing wells that are shown to be no longer useful will be abandoned. The first three years of evaluation monitoring will measure area background concentrations, concentrations at the point of compliance, establish a statistically significant database of existing contaminant concentrations in each monitoring well, and demonstrate that groundwater gradients in the deep and shallow aquifers support the design of the groundwater monitoring well network. For the first two years, monitoring wells will be monitored quarterly in accordance with a sampling and analysis plan approved by the City and Ecology. After the first two years, monitoring will occur semi-annually, using a parameter list narrowed to include only compounds that appear to be present or are of concern. Performance monitoring will be conducted semi-annually for a minimum of ten years after evaluation monitoring is completed. Performance monitoring of the shallow aquifer involves FINAL - March 2001 4-2 Everett Landfill Tire Fire Site Cleanup Action Plan 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1