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source test, MW10 was disconnected from the blower and the two risers in the tank field were connected for a duration of 1/2 hour to obtain source samples that could be generated from the tank backfill. 6.2 PILOT TEST Gasoline range hydrocarbons are known to exist beneath the underground storage tanks area. The tank excavation was overexcavated to the 26 foot depth. on December 27-28, 1990, monitor well MW10 was manifolded to the allanmtub scrubs wer0e January 3, 1991, activated charcoal in 85 g delivered to the site. The blower was installed on January 7, 1991, and a few days later, the test was begun. The test was conducted for five days (January 11-January 151 1910) . Break through was noted from a sample obtained on January 14 and analyzed on January 15, 1991- At this time the system was sampled, shut down, and disconnected. 6.3 TEST PROCEDURES Vapor extraction well MW10 was connected to a vacuum system (1HP Rotron Blower) that exhausted into 85 gallon activated charcoal tub scrubs. Sample ports were located at excavation wellsdEXI and EX2 and monitor wells MW1, MW2, MW3, MW4, MW6, obtaining vacuum/pressure and vapor readings during the test. Also sample ports were located at the intake of the blower, the exhaust of the blower, and the exhaust of the charcoal. The exhaust from the tub scrubs was checked daily for breakthrough using a hand held photoionizing detector (PIU) that was calibrated to 50 ppm Isobutylene in air. Breakthrough was assumed to be a reading of 500 on the PID. On January 14, 1991, the PID registered 250, and a slight odor was noted from the exhaust of the charcoal. A bag sample way then obtained and brought back to Western Geo-Engineers portable laboratory in Woodland, California, late in the evening. The sample was immediately run the next morning and determined that breakthrough had occurred. The pilot test was then terminated that day, see Tables 1 and 2 of Appendix C. During the source test, bag samples were obtained from monitor well MW10 and showed a relatively stable vapor stream cofsiTatal of 119 to 164 mg/L (31,000-42,700 ppm gasoline vapor) Fuel Hydrocarbons (TFH) in air along with 14% methane (Stockton area is a known basin. for natural gas production and it is believed that this methane is produced from the underlying formations and not from a leak in the gas main) . At the completion of the test the extraction system was connected to the excavation wells so samples could be obtained from that source area. steady state was probably not reached in the excavation during the short 1/2 hour duration. of vapors being ' pulled 11