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Ms. Wendy Arano Project No. 809251 July 26, 2000 Page 4 summarized on Table 2. Copies of certified analytical reports and chain of custody documents are presented in Attachment C. Landfill Gas Well Sampling and Analysis Gas samples were collected from the three landfill gas monitoring probes (GW-1, GW-2, and GW-3) located along the northern property line using a GEM Lantec 5000. Methane, oxygen, and carbon monoxide levels were also recorded. These probes monitor the vadose zone in contact with the shallow perched groundwater. The landfill gas samples were submitted to Performance Analytical and analyzed for VOCs using USEPA Method TO-14A Twelve VOCs were detected in landfill gas samples collected from the vadose zone. Analytical results are summarized on Table 2. Copies of certified analytical reports and chain of custody documents are presented in Attachment C. Evaluation of Analytical Results Comparison of the landfill vadose zone analytical results to the MW-5 analytical results shows a correlation between VOCs in gas and nerchcd g;@u a•=&4ter. TheVOCs detected in landfill gas appear to be the source of groundwater impacts in the shallow perched water-bearing zone. Four of the VOCs detected in groundwater at n the method remrtillg limit are present in landfill gas at concentrations ranain.R from three to five order a de a ove-the res echv''!''-dissolved concen ations in dwater. hese results support the SWD and IVEMCON opinion that landfill gas is the source of the VOCs detected in groundwater. FINDINGS AND CONCLUSIONS Three exploratory borings drilled to depths of 67 to 82 feet bgs did not encounter the shallow perched groundwater zone to the west of MW-5. Soil samples collected from the clay unit were damp to moist, however, saturated conditions were not encountered either perched above or to depths of 15 feet into the clay unit. The absence of groundwater in the soil borings further delineated the extent of the shallow perched water bearing zone and shows that shallow groundwater is limited to the eastern part of the site. VOC concentrations in the landfill gas samples and in the groundwater sample collected from MW-5 showed correlation between the VOCs present within landfill gas and groundwater. The data support the belief that landfill gas is the source of the shallow groundwater impacts. it coav� on SAC:\N:\Consulting\data\Shared\Projects\PJ8\809251.aa.doc-00\ta:l 809251