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S E C 0 R � W July 1997 through December 1998—Tosco consultants performed the following tasks 1) conducted an underground utility search (ERI, October 6, 1997), 2) continued to perform quarterly groundwater monitoring and sampling, 3) obtained access agreements to drill soil borings at select properties located south and southwest of the site, 4) requested Sequoia Analytical Laboratories (Sequoia) to review chromatograms of groundwater samples collected during the September 1995 Geoprobe® investigation (Delta, February 6, 1996) in order to estimate methyl tertiary butyl ether (MTBE) concentrations in groundwater(ERI, March 2, 1999) • February 1999—Tosco consultants advanced three off-site cone penetrometers (CPT1 through CPT3) and drilled three off-site soil borings (138 through B10) (ERI, March 2, 1999) • April 1999 —Tosco consultants installed nine off-site groundwater monitoring wells consisting of three nested wells (shallow, intermediate, and deep) at each of three well locations (ERI, June 9, 1999) • May 1999—Tosco's consultant ERI submitted a report entitled Air Sparge/Sar! Vapor (AS/SVE) Extraction Test, dated October 18, 1999, presenting the data collected during ERI's May 1999, AS/SVE feasibility test • December 28, 1999—Tosco's consultant ERI submitted a Corrective Action Plan (CAP) Tosco received a letter from the San Joaquin County Public Health Services department (the County) dated February 22, 2000, approving the remediation recommendations provided in ERI's December 28, 1999 CAP as an Interim Remedial (IR)Action document • 0 During second quarter 2000, Tosco consultant ERI installed one UST cavity well in general accordance with the CAP (ERI, December 28, 1999) Periodic purging of groundwater from the UST cavity well and from groundwater monitoring well MW3 was also initiated Groundwater purging was temporarily discontinued during third quarter 2000 pending clarification from the County regarding water sampling and data collection January 2002, when it was terminated following installation and operation of the s microsparge remediation system Approximately 285,000 gallons of groundwater were purged from the UST cavity well and well MW3 and transported to the Tosca refinery for recycling during interim groundwater remediation efforts • During June 2001, contractor Tracer Research Corporation 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, consultant ERI submitted an additional 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 maintenance (O&M) of the system Currently, there are ten on-site AS wells (AS1 through AS5, AS7, AS8, and AS10, and nested wells AS6S/D and AS9S/D), three on-site, single-casing groundwater monitoring wells (MW1 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 MW10Sll/D) consisting of three wells nested at each location