SU0007861 - Laserfiche WebLink

Home Browse Search

Draft Environmental Impact Report Page IVY-16 Forward Inc. Landfill Expansion FThe common landfill gases methane and carbon dioxide, on the other hand, are not introduced with refuse as contaminants but are the product of natural decomposition of refuse. Methane and carbon dioxide are the typical landfill gases, with stipulated CIWMB requirements in California for their monitoring.and capture. Contaminant distribution patterns have been evaluated extensively over the last few years,with F1 particular focus on the leachate plume migrating offsite to the north of the Forward Landfill downgradient toward the NCYCC. Data from the various studies was utilized in the groundwater flow and transport model(AEE and Herst&Associates,2001b). The distribution of both landfill gases and VOCs in the groundwater show most of the contaminant volume is F. associated with the area of the former Austin Road Landfill and—for the contaminated groundwater plume—north of it. The evaluation of an appropriate remedy to mitigate against current and future VOCs in groundwater has been addressed in the JTD (2001, through 2007 E)l updates), in part,by proposing that the migration of VOCs in the groundwater can be controlled and reduced through VOC capture by the expanded landfill gas collection system since the VOCs volatilize and circulate within landfill gas and can therefore be removed through the gas collection and gas condensate collection system. k The expansion areas proposed,being upgradient from other parts of the landfill, would rely in large part on the existing Forward monitoring well arrays. The Forward.Landfill, initiated in 1973,has had a groundwater-monitoring program since 1977. There are 31 monitoring wells, 17 associated with Forward Landfill unit and 14 monitoring wells associated with the Austin Road Landfill unit. Both landfill units have supply wells. Ten of the monitoring wells (MW1, MW4, MW6,and MW7 through MW13) are downgradient of the landfill, and three wells (MW2, MW3, and MW5) are located upgradient of Austin Road unit and between Forward and Austin Road Landfill unit. Figure IV.F-1 shows the existing monitoring well layout. One of the former Austin Road landfill water supply wells (WSW), located just east of monitoring well MW-4 was decommissioned in compliance with Waste Discharge Requirements Order Number 90-122 due F to contamination(R.W. Beck and Associates, 1993). This well was screened to a depth of 82-116 feet, indicating contamination had migrated downward to that depth. Groundwater samples from production wells, monitoring wells, and hydropunch bores are tested on a monitoring F program approved by the RWQCB for VOCs. Chlorinated halocarbons, also referred to as volatile organic compounds, are the only chemicals of current regulatory concern detected. The contaminated groundwater plume geometry is shown in Figure IV.F-2. Data for this figure a was from a compilation of sources, including the three offsite wells to the north at the NCYCC the most distant of which is about 5,500 feet downgradient (north) from the Forward Landfill border. This plume is indicate to have a due north and a northeastern component based on the detection of PCE in the private offsite wells 7898 and 8106A and in the NCYCC wells. Well ARL 1B and ARL 2a show no detections. Depth and screen differences in the wells may account for VOC detection differences. Water quality monitoring since 1989 has shown VOCs at concentrations of regulatory concern. q Y g The 2000 Austin Road supplemental EIR reported the key VOC contaminants as: tetrachloroethene (PCE);trichloroethene (TCE);cis-1,2-dichloroethene (DCE);and vinyl chloride (VC). Groundwater contamination is mainly attributed to the historical operations and leachate and landfill gas generation at the Austin Road landfill rather than the Forward landfill. Groundwater beneath the Forward Landfill unit flows northward downgradient beneath the Austin Landfill landfill unit. r- b .