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6.2 AMBIENT AIR QUALITY <br />Benzene, methylene chloride, tetrachloroethylene, carbon tetrachlo- <br />ride, 1,1,1 -trichloroethane, and trichloroethylene were detected in <br />one or more ambient air samples. Benzene, carbon tetrachloride, and <br />1,1,1 -trichloroethane concentrations were at or below their respective <br />regulatory detection limits. Methylene chloride, carbon tetrachlo- <br />ride, and trichloroethylene were only detected in downwind ambient air <br />samples. The concentrations of the other VOCs (benzene, tetrachloro- <br />ethylene, and 1,1,1 -trichloroethane) were relatively similar in upwind <br />and downwind ambient air. <br />6.3 GAS MIGRATION <br />No total organic compounds measured as methane were detected in <br />Probe P-1 (3 ppm detection limit). The methane concentration in <br />Probe P-2 was 2 ppm. For the other two probes, P-3 and P-4, the <br />methane concentrations were 24 and 9 percent by volume, respectively. <br />Probe P-1 is located between the fill area and the manager's <br />residence, on the western side of the site. The P-1 results indicate <br />that there is no gas migration to this residence. <br />Except for Probe P-2, the four probes were within 50 feet of the fill <br />area. Probe P-2 is over 400 feet north of the fill area. The <br />presence of 24 and 9 percent total organics measured as methane at the <br />site boundaries at P-3 and P-4 indicates a potential for off-site <br />landfill gas migration. However, no residential housing exists near <br />these probes. <br />PJ9 9390405.00D 6-2 Rev. 0 09/07/88 <br />Emcon Associates <br />