ARCHIVED REPORTS_2001 - Laserfiche WebLink

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• 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 6°9 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 conceatrations away from:athe landfa] 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. It is possible that the VOC impacts in groundwater at the existing Austin Road Landfill are attributable to landfill gas. VOC concentrations have been trending downward recently, and leachate analyses from the existing Austin Road Landfill indicate no significant VOCs. VOCs are detected, however, in landfill gas samples. Forward is currently assessing landfill gas and groundwater issues at the existing Austin Road Landfill and, as required by the RWQCB, a revised Forward Landfill jTD 3-16 L:\Allied\2000.193\Reports\fi naljtd:Sec-3.0:08/20/01 BRYAN A.STIRRAT&ASSOCIATES