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3-14 Based on a review of the existing data, the GLA report concluded that several factors suggest that landfill gas production in WMU B was a significant contributing source of VOCs in the groundwater at the Forward Unit. These factors include: the locus of VOC detections near unlined landfill cell WMU B, the erratic pattern of low VOC detections, the relative long list of VOCs that are detected, the detection of VOCs in both upgradient and downgradient monitoring wells, and the consistency of inorganic water quality in both upgradient and downgradient wells near the site. GLA concluded that the potential impacts associated with the VOCs in the groundwater appear to be small because the concentrations of VOCs are well below drinking water standards and the absence of VOCs at offsite monitoring locations indicate that VOCs degrade or disperse within a relatively short distance of the landfill boundary. Subsequently, a landfill gas collection system was installed in WMU B to address the VOC issues and VOCs have not been recently detected in the WMU B area. Additional landfill gas extraction wells are installed, as needed, at the landfill. At the Austin Road Unit (while under ownership of the City of Stockton), a Solid Waste Quality Assessment Test (SWAT) in 1989 found a significant groundwater quality impact downgradient from the unlined Austin Road Unit. Several VOCs were found in the downgradient monitoring wells. An EMP was implemented in three phases to determine the vertical and horizontal extent of contamination. Phases I and II confirmed VOC impacts along the entire downgradient edge of the landfill and in the first encountered water bearing zone. Phase III indicated the chlorinated hydrocarbon impacted groundwater extends laterally as far as 1,000 feet downgradient of the edge of the landfill. A Corrective Action Program (CAP) was proposed in 1991 by the City of Stockton to address the chlorinated hydrocarbon (i.e., VOCs) impact to groundwater. The plan was approved by the RWQCB in June 1991 and involves the following actions: ♦ Reduction of leaching of chlorinated hydrocarbons (i.e., VOCs) 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. The City's CAP, which began operations in 1994, was designed to address the VOC impacts to groundwater through a pump and treat system where groundwater is extracted at the northern boundary of the Austin Road Unit and treated through an air stripper. The groundwater Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\jtd-5 yr pr 2013\text\sec 3_final.doc