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' �-- %Tc ATC Associates Inc <br /> 1117 Lone Palm Avenue, Suite B <br /> Modesto, California 95351 <br /> (:Vyj 209-579-2221 <br /> A S S O C I A T E S I N C <br /> fax 209-579-2225 <br /> In December 2001, sail-bonng VEWI was advanced to approximately 35 feet bgs, and borings <br /> VEW2 and VEW3 were advanced to approximately 45 feet bgs Borings MW5, MW6, and MW7 <br /> ' were advanced to approximately 65 feet bgs Soil borings VEWI, VEW2, and VEW3 were <br /> completed as 2-inch diameter vapor extraction wells and soil borings MW5, MW6, and MW7 <br /> ' were completed as 2-inch diameter groundwater monitoring wells Boring CPT 1 was advanced <br /> to approximately 100 feet bgs utilizing a truck-mounted cone penetration test (CPT) rig A soil <br /> vapor extraction pilot test was conducted which yielded a radius of influence (ROI) of <br /> approximately 30 feet, at a vacuum of 115 inches of water Approximately 2 64 pounds of total <br /> petroleum hydrocarbons quantified as gasoline (TPHg), benzene, toluene, ethylbenzene, and <br /> xylenes (BTEX) were removed during the vapor extraction pilot test Soil vapor extraction <br /> ' appeared to be a viable method for remediating TPHg and BTEX impacted soil at the site Field <br /> activities and analytical results are detailed in ATC's Remedial In vesagahon/Feasibihty Study, <br /> dated November 19, 2002 <br /> Historical soil and groundwater analytical data is presented in Tables I and 2, respectively <br /> ' 4.0 HIGH VACUUM DUAL PHASE EXTRACTION <br /> High vacuum dual phase extraction events were performed at the site in an effort to remediate the <br /> hydrocarbon-impacted vadose and capillary fringe zone soils The methods and procedures and <br /> the results are discussed in the following sections <br /> ' 4_1 Hiah Vacuum Dual Phase Extraction Methods and Procedures <br /> From October 2004 through April 2005, ATC performed six monthly high vacuum dual phase <br /> extraction events at the site During the initial event, ATC extracted from wells VEWI, VEW3, <br /> and MW2 to compare extraction removal rates The volatile fuel hydrocarbon (VFH) <br /> ' concentration was monitored in extracted vapors from each well using a photo ionization detector <br /> (PID) Based on the PID readings, high vacuum dual phase extraction remedial action was <br /> conducted using existing vapor extraction well MW2 as a source well MW1, MW3, MW4, <br /> VEWI, VEW2, and VEW3 were used as observation wells The remedial action was conducted <br /> during monthly events, each having a duration of approximately five days or forty hours Vacuum <br /> influence and depth to water was monitored at the observation wells to evaluate the radius of <br /> vacuum influence and groundwater draw down During the remedial action the soil gas oxygen <br /> concentration was monitored using a GasTechTm combustible vapor analyzer The VFH <br /> concentration was monitored with a PID During the events, soil gas samples were collected in <br /> ' Tedlafm bags for laboratory analysis for VFH, BTEX and MTBE using EPA Test Method TO- <br /> 14 <br /> ' The high vacuum dual phase extraction remedial action was conducted using mobile extraction <br /> equipment having a hquid-ring blower and associated flow rate and pressure measuring <br /> equipment During the remediation period, an equipment malfunction occurred with the high <br /> vacuum system Ms Lon Duncan of EHD verbally approved the use of a standard 5 horsepower <br /> 3\eI►vn-o�w2577-Diesel PerRTeportsVnterlm rem.doc 3 <br />