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September 18, 1996 ` Page 5 1 The estimated distance downgradient from Well MW-1'I to the - 10 parts per billion (ppb) concentration contour would be 165 feet 2 The estimated time it would take to degrade the initial dissolved benzene concentration in Well MW-11 (1,500 ppb) to110 ppb would 1 I take 7,197 days or 20 4 years t December 1993. Three 50-foot confirmatory soil borings (SB-1, SB-2, and SB-3) were drilled by GTI near the former 10,000-gallon gasoline UST complex to determine the effectiveness of the SVE system (Figure 2) In addition, two 66 5-foot borings were drilled and converted to Wells MW-2R and MW-14 to replace Well MW-2, and to further define the downgradient 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 bgs in Boring SB-2 and also at 30 feet bgs in Boring SB-3 No benzene was detected in any samples analyzed (Figure 2, Table 2) While drilling the boring for Well MW-21R, one additional unknown UST was encoun- tered at a depth of approximately 4 feet bgs near the southeast corner of the site (Figure 2) GTI retained Spectrum Environmental Services, Inc to conduct a geophysi- caI 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, 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 bdnngs 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 ofthe,former 10,000-gallon gasoline UST complex The maximum concentrations detected in samples from Borings SB-10 through SB-13 were 2,400, 240, 5,300, and 10,000 ppm, respectively at between 25 and 30 feet bgs REMEDIATION ACTIVITIES AND EFFECTIVENESS Site remediation to date has consisted of removing product storage and distribution equipment,,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 Septem- ber 1992 The system was shut down due to low influent concentrations The wells used to remove vapor-phase hydrocarbons were V-1 through V-5, and Monitoring Wells MW-3 through MW-6, screened from approximately 14 to 44-feet bgs (Figure 2) 320 i 337B1CLOSLJRE1 t 1