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November 12, 1996 Page 4 t tank Dunng tank excavation, product piping was uncovered leading to two additional steel USTs (3,000- and 4,000-gallon) that had been abandoned in place and filled with soil December 1988. The three additional steel USTs were removed and documented`by Blaine Tech Services, Inc (Blaine) Prior to excavation the liquid inside of the 550-gallon UST was pumped, and soil inside the 3,000- and 4,000-gallon tanks was removed Upon excavation, no holes in the tanks were observed One soil sample was y collected below each end of the 4,000-gallon tank (Samples EF#1 and EOP#4), and below each end of the 3,000-gallon tank (Samples FOP#2 and FF#3), and one soil sample was obtained from below the middle of the 550-gallon tank (DM#5) No petro- leum hydrocarbons, ethylene dibromide, or organic lead was detected in any sample analyzed (Table 2) January 1989.`EA drilled seven borings and completed them as five soil vapor extrac- tion (SVE) wells (V-1 through V-5), and two groundwater monitoring wells (MW-7 and ,MW-8) The maximum concentration of petroleum hydrocarbons were reported at 26 5 feet bgs in the sample collected from Boring V-3 (16,000 ppm TPPH-g and 160 ppm benzene), drilled through the center of the former 10,000-gallon gasoline tank complex (Figure 2) April 1989 EA conducted a pilot-scale test utilizing SVE Wells V-2 through V-5 to determine the design parameters for,a vapor extraction system to remediate areas of hydrocarbon-impacted soil on site Vapor samples from Wells V-2 and V-5 contained concentrations of TPPH-g up to 4,500 and 16,000 ppm, respectively, and a radius of influence of at least 22 feet was calculated indicating that SVE was a practical approach November 1990. SVE was initiated The SVE system was operated from November 1990 until November 1992, with a 7 month hiatus from February to September 1992 f Results of SVE operation are presented in a table included in Attachment A Between July 1991 and June 1993. Groundwater Technology, Inc (GTI) completed five groundwater monitoring wells (MW-9 through MW-13) and one SVE well (V-6) The groundwater monitoring wells were completed to a maximum depth of 75 feet bgs and SVE Well V-6 was completed to 29 feet bgs TPPH-g and benzene were only detected in the samples collected from the borings for Well MW-9 and SVE Well V-6 `The sample collected at 26 feet bgs in the boring for Well MW-9 located proximal to the ' northern corner of the former UST complex reported the maximum concentration of petroleum hydrocarbons at 3,900 ppm TPPH-g and 1 7 ppm benzene (Figure 2, Table 2) 's 1 a ' f 3201337aCLOSUR£2 1 t - t