SITE INFORMATION AND CORRESPONDENCE

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FROM : 1997." -14 17:44 11888 P.07/24 rebruary_ 14, 1997 Pa,e 6 U further define the down�,radient extent of petroleum hydrocarbons in groundwater, respectively. Of the 30 soil samples collected, the maximum concentration of petroleum hydrocarbons of 2,000 ppm TPPH-g was reported at 25 feet bas in Boring SB-2 and also at 30 feet bgs in Boring S5-3. No benzene was detected in any samples analyzed (Figure 2, Table 2). While drilling the boring for Well MW-2R one additional unknown UST was encoun- tered at a depth of approximately 4 feet bas near the southeast corner of the site (Figure 2). GTI retained Spectrum Environmental Services, Inc. to conduct a geophysi- cal survey of the former service station property in an effort to locate other USTs that were not identified previously. No other USTs were found during their investigation. March 1994. Touchstone Developments excavated and removed one 1,000-gallon UST and associated product piping from the site. One soil sample was collected at 8.5 feet bgs below each end of the gasoline tank(Samples TW-8-1/2' and TE-8-1/2'),but no petroleum hydrocarbons were detected. May 1994. GTI drilled six soil borings(SB-4 through SB-9) near the former locations of the USTs and dispensers(Figure 2). A total of 30 soil samples were analyzed from the borings. No petroleum hydrocarbons were detected in any sample analyzed (Table 1). June 1995. GTI drilled four additional confirmatory soil borings (SB-10 through SB-13) in the vicinity and northeast of the former I0,000-gallon gasoline UST complex. The maximum concentrations detected in samples from Borings SB-10 through SB-l3 were 2,400, 240, 5,300, and 10,000 ppm, respectively at between 25 and 30 feet bgs (Table 2). REMEDIATION ACTIVITIES AND EFFECTIVENESS Site remediation to date has consisted of removing product storage and distribution equipment, limited overexcavation to approximately 25 feet below'ground surface,and operation of the SVE system. The SVE system was operated from November 1990 until November 1992, with a 7 month hiatus from February to September 1992. The system was shut down due to low influent concentrations. The wells used to remove vapor-phase hydrocarbons were V-I through V-5, and Monitoring Wells MW-3 through MW-6, screened from approximately 14 to 44 feet bgs(Figure 2). The vacuum radius of influence was estimated to be in excess of 25 feet,for Wells V-1 through V-5. A subsequent vacuum radius of influence analysis was performed on Well MW-4, resulting in an estimated effective radius of 112 feet. During'the SVE, program, an estimated total of approximately 12,000 pounds (1;967 gallons) of petroleum hydrocarbons were removed(Corrective Action Plan, PACIFIC, November 30, 1995). System operational 3201337PICLOStMM