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r 5. <br /> January 10, 1996 <br /> Page 2 <br /> M <br /> located in the southwestern corner of the site At the same time, the former 550-gallon <br /> used oil tank was replaced with a 1,000-gallon tank <br /> PREVIOUS INVESTIGATION <br /> Soil and groundwater investigations at the site have been conducted by Groundwater <br /> Technology, Inc , Dames and Moore, and Sierra Environmental Services Investigative <br /> work included a soil vapor survey, installation of groundwater monitoring wells (MW-1 <br /> through MW-7), soil sampling of the former USTs excavation, and a limited records <br /> search for potential off-site sources Figure 1 presents historical soil analytical data The <br /> findings of these investigations are summarized below <br /> Soils beneath the site consist of interbedded clayey, silt and sand <br /> 4 Historically, average groundwater elevations have ranged from -43 47 <br /> to -35 61 feet mean sea level (MSL) Current depth to groundwater at <br /> the site ranges from approximately 46 to 47-1/2 feet below ground <br /> surface (bgs) <br /> o Groundwater flow is to the southeast <br /> * Total purgeable petroleum hydrocai bons calculated as gasoline <br /> (TPPH-g) were not detected in soil by the soil vapor study <br /> o TPPH-g was detected in only one soil sample Froin beneath the former <br /> UST excavation (56 parts per million [ppm]) TPPH-g and benzene <br /> were not detected in soil samples from borings for the perimeter <br /> groundwater monitoring wells <br /> ® TPPH-g and benzene have been consistently detected in groundwater <br /> Monitoring Well MW-2 (maximum concentrations of 1,200 and <br /> 840 parts per billion [ppb], respectively) TPPH-g and benzene have <br /> been sporadically detected in Wells MW-4 and MW-5 TPPH-g and <br /> benzene have not been detected in Well MW-7 which is located down- <br /> gradient of the former product islands and piping <br /> o A chlorinated plume occurs in the site vicinity as a result of releases <br /> from several dry cleaning facilities This plume extends beneath the <br /> Chevron site The chlorinated compounds that have been identified <br /> beneath the site include 1,2-dichloroethane, 1,1-dichloroethane, <br /> trichloroethene, and tetrachloroethane Tetrachloroethene has been <br /> identified at a concentration of 10,000 ppb beneath the site <br /> 3201351 AIREPQRT <br />