ARCHIVED REPORTS_2002_3 JTD - Laserfiche WebLink

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• Reduction of leaching of chlorinated hydrocarbons into the groundwater by checking incoming loads into the landfill for hazardous materials and implementing measures to reduce storm-water infiltration into the refuse; • Extraction of groundwater from two wells to reduce the off-site migration of chlorinated hydrocarbons; • Installation of an above-ground treatment system to remove VOCs from the extracted groundwater prior to discharge; 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 Road Landfill. The plume appears 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 up to 69 and 48 micrograms per liter (pg/L), respectively. The highest VOC concentrations are present within a sand layer that extends over an interval of approximately 80 to 104 feet below ground surface (bgs). The investigation results indicate that contaminant concentrations decrease at distances from the source, with the plume migrating in deeper lithologic units at� a distance from the site. The plume shape reflects the north to northeast groundwater flow direction, with the leading edge of the plume extending east of Austin Road. The contaminant plume is moving at a similar rate, approximately 4 feet per day, as the general groundwater flow rate. This suggests that VOC migration rates are not affected significantly by sorption of contaminants to aquifer materials. 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. Bottled water is supplied to all downgradient well owners where there has been a detection of any VOCs above drinking water standards. This has been performed since 1997 when downgradient wells first detected PCE above 5 pg/L. Forward Landfill JTD 3-16 L\Allied\2000.193\Reports\Jtd:Sec-3.0:05/21/02 BRYAN A.STIRRAT S ASSOCIATES