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TERRA <br /> VAC <br /> 14798 WICKS BOULEVARD pup( �q�argc�;rnl ■TEL (510) 351-8900 <br /> SRN LEANDRO, CALIFORNIA 945 ui io ■ FAX (510) 351-0221 <br /> April 12, 1995 P�ktl� <br /> Mr. Brett Hunter MAY 19 v <br /> Chevron U.S.A. Products Company E 1995 <br /> San1 Bollinger Canyon Road <br /> Ramon, California 94583-0804 NPE N Rj 1c tAaN <br /> Subject: Dual Vapor Extraction Test <br /> Former Chevron Service Station 9-4054 <br /> 7103 Country Club Drive, Stockton, California <br /> Dear Mr. Hunter: <br /> On March 16, 1995, Terra Vac performed a dual vapor extraction (DVE) test at the subject site. <br /> A rotary lobe vacuum pump, liquid/vapor separator, and associated monitoring equipment were <br /> mobilized to the site and powered by a portable generator. This equipment is identical to <br /> equipment that would be used in a full-scale DVE system. The purpose of performing the test <br /> was to determine if DVE is a appropriate method for remediating impacted soil and groundwater <br /> at the site. <br /> The subject site is a former Chevron service station. Underground storage tanks have been <br /> removed and aboveground structures demolished. A review of assessment data indicates that <br /> hydrocarbons are present in the vadose zone soil and dissolved in groundwater. Additionally, <br /> during recent drought years, static water levels beneath the site were five to seven feet lower <br /> than at present. Large amounts of hydrocarbons are likely sorbed onto soils located within this <br /> "smear zone". In order to achieve "no further active remediation" for the site, these <br /> hydrocarbons will have to be removed. The DVE approach is to simultaneously remove soil <br /> vapor and groundwater from the subsurface. As groundwater is removed, the water table is <br /> depressed, exposing these soils to direct remediation via vapor extraction. Depth to water levels <br /> recorded at the site during drought years were in the range of 22 feet. Current depths to water <br /> are approximately 15 feet. In order to provide effective direct remediation of"smear zone" soils, <br /> a minimum water drawdown of 10 feet would be required in each extraction well. <br /> Terra Vac performed testing on three existing groundwater monitoring wells (MW-1, MW-2, <br /> and MW-3). Static water levels were measured in each of the wells before the start of testing. <br /> The vacuum blower was used to generate a vacuum induced flow in a suction pipe. As the <br /> suction pipe was lowered below the static water level in any given well, groundwater became <br /> entrained in the vapor flow and was removed from the well. Entrained groundwater was <br />