ARCHIVED REPORTS_2008_29 - Laserfiche WebLink

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• Installation of an above-ground treatment system to remove VOCs from the extracted groundwater prior to discharge, and which was expanded to include discharge to a recharge area beginning in May 2003; and • Monitoring the effectiveness of the corrective action and determination of the need for modifications. In order to better understand the dimensions and impacts of the plume, the RWQCB ordered further investigations to be conducted. In January 1999, Camp Dresser & McKee (CDM) prepared the "Austin Road Landfill Contaminant Plume Report" and the "Groundwater Corrective Action Feasibility Study Report". Based on these reports, the VOC contaminant plume was estimated to extend approximately 4,000 feet northeast from the northern border of the existing Austin Unit of the Landfill. The plume appeared to have migrated to a lower depth at the leading edge of the plume. The primary contaminants of concern are PCE and TCE, with concentration levels measured at up to 69 and 48 micrograms per liter (fag/L), respectively, though the concentrations have declined more recently. The investigation identified the highest VOC concentrations within a sand layer that extends over an interval of approximately 80 to 104 feet below ground surface (bgs). The investigation results indicated that contaminant concentrations decrease at distances from the source, with the plume migrating in deeper lithologic units at a distance from the site. The trend of reduced contaminant concentrations away from the landfill is attributed primarily to dilution occurring through mixing with unimpacted groundwater and with surface water recharge. The groundwater impacts identified above originate from the unlined units of the original Forward and Austin Road Landfills. Current and proposed operations include a rigorous load checking program for incoming waste and construction of state-of-the-art composite liner systems to separate landfilled waste from the environment. Forward Landfill-Project Description 2-15 BRYAN A.STIRRAT&ASSOCIATES J:\Allied\Forward\2007.0018 Lateral Expansion\Reports\Prof Descrip\021308 Final Proj Des\Sec 2.doc:2/13/2008)