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November 12, 1996 <br /> Page 6 <br /> �*�­bgs below each-eiid of the gasoline ta6r— Shcmples TW=8=112'an&TE=8=1%2');but not" l - -- <br /> petroleum hydrocarbons were detected ' <br /> May 1994. GTI drilled six soil borings (SB-4 through SB-9) near the former locations <br /> of the USTs and dispensers (Figure 2) A total of 30 soil samples were analyzed from <br /> the bonngs No petroleum hydrocarbons were detected in any sample analyzed <br /> (Table 1) <br /> June 1995. GTI drilled four additional confirmatory soil borings (SB-10 through <br /> SB-l3) in the vicinity and northeast of the former 10,000-gallon gasoline UST complex <br /> The maximum concentrations detected in samples from Bonngs SB-10 through SB-13 ' <br /> were 2,400, 240, 5,300, and 10,000 ppm, respectively at between 25 and 30 feet bgs <br /> (Table 2) <br /> REMEDIATION ACTIVITIES AND EFFECTIVENESS <br /> Site remediation to date has consisted of removing product storage and distribution <br /> equipment, limited overexcavation to approximately 25 feet below ground surface ,and <br /> operation of the SVE system The SVE system was operated from November 1990 <br /> until November 1992, with a 7 month hiatus from February to September 1992 The <br /> system was shut down due to low influent concentrations The wells used to remove <br /> vapor-phase hydrocarbons were V-1 through V-5, and Monitoring Wells MW-3 through <br /> MW-6, screened from approximately 14 to 44 feet bgs (Figure 2) The vacuum radius <br /> of influence was estimated to be in excess of 25 feet, for Wells V-1 through V-5 'A <br /> subsequent vacuum radius of influence analysis was performed on Well MW-4, resulting <br /> man estimated effective radius of 112 feet Dunng the SVE, program, an estimated <br /> total of approximately 12,000 pounds (1,967 gallons) of petroleum hydrocarbons were <br /> removed (C orreCl7ve Action Plan, PACIFIC, November 30, 1995) System operational <br /> data including influent concentrations, flow rates, and the operating time is presented in <br /> the table included in Attachment A <br /> The calculations for determining TPPH-g mass in soil and groundwater utilized soil <br /> boring and analytical data to estimate the area] extent of the hydrocarbon plume Aver- <br /> age concentrations were applied to distinct cross sectional areas in order to arrive at the <br /> total hydrocarbon mass both prior to and after SVE treatment Figures 3 through 5 <br /> depict soil conditions beneath the site prior to operation of the SVE system (November <br /> 1990 -November 1992) Figures 6 through 8 depict these conditions and show soil <br /> analytical data from soil borings and wells drilled after the operation of the SVE system <br /> Well construction details are presented on the boring logs included in Attachment C <br /> Calculations for determining the TPPH-g mass in soil before and after the operation of <br /> the SVE system are presented as Attachment A Details of the methodology used to <br /> i <br /> 3201337i31CL OSLTRE2 <br />