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wells. A landfill gas extraction system was installed in 1996. The most likely release that will require corrective action is an elevation in VOCs rather than an elevation of inorganics. Older landfill gas systems were not designed to control the migration of landfill gas from the unlined bottom of the landfill. Using past performance of the module as an indicator of possible future release mechanisms, escape of landfill gas from the Unit is probable and more likely than generation of leachate as a mechanism for moving contaminants from the bottom of the landfill to groundwater. The hypothetical release scenario for Harney Lane Sanitary Landfill is as follows: • Release occurs from the unlined landfill in three directions • Deep landfill gas (carrying VOCs)beyond the influence of the existing landfill gas extraction wells escapes from the bottom,of the landfill. • The escaped landfill gas travels to groundwater resulting in low level (<50 µg/1) VOC concentration in groundwater. HYPOTHETICAL EVALUATION MONITORING PROGRAM An Evaluation Monitoring Program(EMP) will be conducted to investigate the lateral and vertical extent of a release from Harney Lane Sanitary Landfill. This EMP will consist of work plan preparation and approval by the agencies, implementation of field investigation and preparation report of the findings. An EMP work plan will be submitted to the RWQCB in accordance with Section 20425 (a) and (b) of Title 27. The EMP will include a soil gas and groundwater step-out/step- down investigation of the western, eastern, and southern boundaries of the site. The proposed investigation will include the following activities: • Installing three hydropunch groundwater zone sampling points and multi-level vadose zone sampling points to the west of the monitoring well MW-4. • Installing three hydropunch shallow groundwater zone sampling points and multi-level vadose zone sampling points to the east of the monitoring well MW-2. • Installing three hydropunch shallow groundwater zone sampling points multi- level vadose zone sampling points to the south of monitoring well MW-3. Corrective Action Financial Assurance Cost Estimate 3 May 25,2007 Harney Lane Sanitary Landfill San Joaquin County Public Works Department