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1 • During the 28 weeks of system operation,more than 17,000 pounds of contaminant was removed ' (2,600 gallons of gasoline equivalent), and 89,000 gallons of groundwater had been extracted and treated Seventy-five percent of soil samples collected contained nondetectable levels of benzene,and detections in the remaining samples were approximately 0 17 mg/kg Confirmatory groundwater samples collected from three wells contained nondetectable levels of BTEX and total volatile hydrocarbons Site closure was ' obtamed in 1991 I4 4.1 3 Release From An Electronics Manufacturing Facility In Texas A drop-tube entrainment system was installed to remediate VOC contamination at the site of a closed surface impoundment at an electronics facility (GSI 1997) The extraction well network consists of 14 wells incorporating drop tubes The wells were installed to 25 feet below ground surface and are spaced ' approximately 20 feet apart The extraction system includes an air-cooled rotary lobe blower, a liquid/vapor separator,a centrifugal silt removal unit, a groundwater transfer pump, a scale inhibitor ' addition system, and piping and accessories necessary to form a connection to existing treatment plant facilities The system vacuum blower was operated at approximately 20 scf n at 20 inches of mercury Soils at the site consist of four principle strata The uppermost unit is a sandy, silty clay with an ' approximate thickness of 10 to 15 feet(Umt 1) Underlying the uppermost unit is a 5 to 8 foot thick layer of silty,clayey,fine sand (Unit II),followed by a 10 to 12 foot layer of sandy, silty,stiff,laminated clay I (Unit III) Beneath the upper three layers is a fossnlnferous, silty shale Groundwater in the vicinity of the site occurs within the silty layer(Unit II) At most well locations,the static water level is at a depth of ' approximately 10 feet below grade The hydraulic conductivity of the saturated silty sand unit averages approximately 6 1 x 10 5 cm/sec At the start of system operation,the affected groundwater plume ranged ' in depth from 15 to 22 feet and extended over an approximate area of 205,000 square feet The plume contained a maximum concentration of 225 mg/L of chlorinated solvents Contaminants of concern included phenol(5 83 mg/L), 1,2-dichloroethane (118 mg/L),methylene chloride (88 mg/L), ' trichloroethylene (8 44 mg/L), and BTEX(0 074 mg/L benzene, 0 305 mg/L toluene,0 018 mg/L ethylbenzene, and 2 95 mg/L xylene,respectively) 4-16 I I