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ERI 205513 OSR22 Tosco Faczluy 5886 Stockton Calxforma October 29,2002 • • During second quarter 2000, ERI installed one UST cavity well in general accordance with the CAP (ERI, December 28, 1999) and Tosco initiated periodic purging of groundwater from the UST cavity well and from groundwater monitoring well MW3 Groundwater purging was temporarily discontinued during third quarter 2000 pending clarification from the County regarding water sampling and data collection requirements Purging was resumed during January 2001, and continued through January 2002, when it was terminated following installation and operation of the microsparge remediation system Approximately 285,000 gallons of groundwater were purged from the UST cavity well and well MW3 and transported to the Tosco refinery for recycling during interim groundwater remediation efforts • During June 2001, Tracer Research Corporation (TRC)performed an enhanced leak detection test on underground storage systems to evaluate the system integrity According to Tosco, the results of the enhanced detection test indicated that the underground storage systems are functioning within acceptable parameters During third quarter 2001, ERI submitted a CAP, dated September 25, 2001 The CAP included recommendations to install a microsparge system to remediate MTBE impacted groundwater beneath the site During first quarter 2002, the microsparge remediation system was completed and ERI performed system startup and initiated monthly operation and mamtenance (O&M) of the system iCurrently, there are ten on-site AS wells (AS I. through AS5, AS7, ASS, and AS 10, and nested wells AS6S/D and AS9S/D), three on-site, single-casing groundwater monitoring wells (MW 1 through MW3), four on-site, dual-casing groundwater monitoring wells (MW4S/D through MW7S/D), one on-site UST cavity well, and nine off-site groundwater monitoring wells (MW8S/l/D through MW IOS/IID) consisting of three wells at each nested well location as shown on Plate 2 and the On-Site Well Locations (Plate 3) Based upon data collected during ongoing quarterly groundwater monitoring and sampling, dissolved hydrocarbons are effectively delineated both laterally and vertically in the vicinity of the site However, dissolved hydrocarbons continue to be detected in groundwater samples collected from on-site wells and are concentrated in the vicinity and downgradlent of the UST cavity THIRD QUARTER ACTIVITIES Based upon previous work completed at the site, and in accordance with the correspondence and request from the County, the following tasks were performed during the third quarter 2002 • ERI performed monthly remediation system O&M and collected monthly groundwater samples from wells MW 1 through MW3 . 3