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11 <br />During 2006 a landfill gas extraction system will be installed in Module 1. The extraction <br />wells extend to a maximum depth of 100 feet below the landfill surface. The maximum <br />waste thickness in Module I is approximately 200 feet. <br />The hypothetical release scenario for Foothill landfill is as follows: <br />1. Release occurs from Module I <br />2. Deep landfill gas (carrying VOCs) beyond the influence of the existing <br />(constructed in 2006) landfill gas extraction wells escapes from the bottom of <br />Module L <br />3. The escaped landfill gas travels to groundwater resulting in low level (<50 µg/1) <br />VOC concentration in groundwater. <br />A corrective action response was developed to mitigate the impacts envisioned under the <br />hypothetical release scenario. The extent and complexity of the corrective action <br />response is proportional to the environment threat of the release and is consistent with the <br />type and magnitude of corrective action mandated by the Regional Water Quality Board <br />at the time this document was prepared. <br />The corrective action envisioned is based on the following assumptions and premises: <br />1. The focus of the corrective action is source control. <br />2. The low level release of VOCs to groundwater will not require active <br />groundwater cleanup (pump and treat, air sparging, etc.). This approach is <br />justifiable given the remoteness of the landfill and absence of surrounding <br />residences. <br />3. The performance objective of the corrective action is to primarily stop increases <br />in VOC concentrations in groundwater and secondarily to reduce VOC <br />concentrations in groundwater over time. <br />Corrective action taken to mitigate the hypothetical release scenario will include the <br />following activities: <br />1. Install 4 deep (approximately 200 feet) landfill gas extraction wells that extend to <br />the base of Module I and are screened to capture deeper gasses. <br />2. The wells will be connected to the existing 12 -inch extraction system header via <br />new 3 -inch laterals and a new 6 -inch secondary header. <br />73467 4 August 9, 2006 <br />LA 31109 Corrective Action Financial Assurance Cost Estimate <br />Foothill Sanitary Landfill <br />