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HydroGeo Consultants Results from groundwater sampling indicated that wells MW-4, MW-6, TB-1, TB-7, and TB-8 all contained greater than 10,000 gg/L TPH and greater than 1,000 gg/L benzene ' Wells MW-3R and TB-10 contained significantly lower levels but had up to 59 gg/L dissolved benzene Well MW-5 has consistently contained free product and therefore was not sampled , A vapor extraction pilot test was conducted in June 1995 by Alton Geosclences and reported in their "Vapor Extraction Test Report", dated August 14, 1995 Thrifty ' prepared a"Corrective Action Plan, Thrifty Service Station#171, 1250 North Wilson Way, Stockton, California", dated September 26, 1995 1n which they proposed to remediate the Site through the use of vapor extraction and groundwater extraction ' Vapor extraction has been performed at the Site since July 1, 1999, using a Baker Furnace Thermal Oxidizer Unit Approximately 62,941 pounds of TPH-g have been , removed and destroyed by the vapor extraction unit as of March 26, 2002 During the 1St Quarter 2002, groundwater sampling results indicated that the highest , concentrations of TPH as gasoline (TPH-g),benzene, and MTBE were detected in monitoring well MW-5 at concentrations of 101,000 gg/L, 7,260 gg/L, and 23,800 gg/L, respectively Other oxygenates detected included di-isopropyl ether(DIPE) in TB-1 and ' TB-8 and turt-butanol (TBA) in MW-3R, TB-1, TB-8, TB-10, and TB-12 Methyl Alcohol (Methanol) was also detected in TB-12 4.0 SCOPE OF WORK 4.1 Aquifer Testing ' 4 9 A 24-hour constant rate aquifer test was performed on well MW-5 on March 16 and 17, ' 2002 Monitoring wells MW-2, MW-3R, MW-4, MW-6, TB-1, T13-7, and TB-10 were used as observation wells during the pumping test Monitoring well MW-5 was also ' gauged for recovery following completion of the pumping test Prior to conducting the pumping test, the static water level was measured in the pumping ' well and observation wells using a 200 foot Sollnst stainless-steel water level meter Depth to water was measured to the nearest 0 01 foot interval The pumping test was conducted using a two-inch stainless-steel variable speed , submersible Grunfos pump which was decontaminated by washing with non-phosphate detergent and triple rinsed with distilled water Two new 50-foot garden hoses were , connected to the pump and the pump was lowered in the well to a depth of approximately 76 feet, total depth of well 82 18 feet below top of casing, and tied off at that depth at the surface with a rope The purge water discharge from the hose was placed in DOT ' approved 55-gallon drums and labeled The purge water was subsequently removed from the Site and recycled . Page 4 TOC 00171 Aquifer Test and RAP Rpt '