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Soil Vapor Extraction Test Results ARCO Facility 2186 Stockton, California Page 2 stored super unleaded gasoline and the two 10,000-gallon USTs formerly stored regular unleaded gasoline The gasoline UST fill ports were located at the northern ends of the tanks Fiberglass piping, located at the northern ends of the USTs, proceeded along the western edge of the site and connected the USTs to two dispenser islands located north of the station building In August 1999 IT Corporation conducted a soil and groundwater assessment consisting of two on-site cone penetrometer test (CPT) borings (CPT-2 and CPT-3) located at the eastern edge of the site and one off-site CPT boring (CPT-1) located to the north of the site Benzene and methyl tertiary butyl ether (MTBE) were detected in water samples collected from CPT-2 Low residual concentrations of total petroleum hydrocarbons as gasoline (TPHG), benzene, toluene, ethylbenzene, and total xylenes (BTEX) in soil remain at depths of 31 to 56 feet bgs The highest detected dissolved petroleum hydrocarbon concentrations have historically occurred in well MW-1 The groundwater flow at the subject site is generally to the northeast to east • A workplan (July 14, 2000) to install offsite groundwater monitoring wells was prepared by Delta and subsequently approved by San Joaquin County PHS/EHD ARCO is currently awaiting authorization from the City of Stockton to access the property where the monitoring wells are proposed to be located FIELD PROCEDURES Three SVE tests were conducted on vapor extraction wells VW-1S, VW-2S, and VW-3S on September 18 and 19, 2000 Field data sheets used to record data during the tests are included in Appendix A Before initiating the test, Delta contacted San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) and notified them of the test schedule and duration During the SVE tests, the wellheads were temporarily modified with appropriate PVC fittings in order to extract soil vapors and convey them to the thermal oxidizer Soil vapors were extracted using a 7 5 hp blower and were abated in a thermal oxidizer (rated at 200 cubic feet per minute [cfm]) before being discharged to the atmosphere Propane was used as supplemental fuel to maintain optimum combustion temperature (1450° F) in the catalytic oxidizer Wells VW-1S, VW-2S, and VW-3S were used as observation wells (see Figure 2) Each wellhead was temporarily modified to monitor the induced vacuum during each vapor • extraction test Magnehelic gages were used to measure induced vacuum in inches of