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9690 S. Austin Road since 1995. The absence of VOCs in the offsite well samples supports the inference that offsite migration of VOCs in groundwater near the FSL is ylimited. 5.0 CONCLUSIONS & RECOMMENDATIONS Quarterly monitoring indicates that VOCs are detected only sporadically and at low concentrations in groundwater monitoring well and lysimeter samples at the FSL. Several factors indicate that the source for the VOCs is landfill gas from WMU-B. 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 1 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. lThe potential impacts associated with the VOCs in groundwater near the FSL appear to be small. The concentrations of VOCs are well below drinking water standards, and the absence of VOCs at offsite monitoring locations indicates that VOCs degrade or disperse within a relatively short distance of the landfill boundary Recognizing that the perimeter landfill gas migration probes were installed only to a depth of about 5 feet, construction of new probes is recommended to provide a better understanding of landfill gas conditions at the site. "Clustered"probe construction should be considered to allow for monitoring of vertical soil horizons. At a minimum, each probe should be completed to the full depth of the landfill cell that it abuts. Quarterly groundwater monitoring should be continued at the site and, whenever possible, should include the 2 nearest offsite wells (i.e., 9621 and 9690 S. Austin Road wells). Although landfill gas-related impacts to groundwater at the FSL have been minor to date, additional landfill gas containment and collection measures are currently being considered. Since landfill gas production is a function of refuse water content, efforts should continue to limit the introduction of precipitation waters to refuse. Such measures include limiting the area of the working face, identifying and eliminating interim fill areas that promote ponding, and applying additional compaction effort on interim fill soils. 6.0 CLOSURE This report is based on the field and laboratory data obtained during routine monitoring and earlier studies of the site. Our firm should be notified if conditions are found that differ from those described in this report, since this may require a re-evaluation of the conclusions and recommendations presented herein. This report has not been prepared for use by parties and projects other than those named or described herein. It may not contain sufficient information for other parties or other purposes. 8 Geologic Associates