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i Ms Margaret Lagono 5 E C ® R October 18, 2005 Page 3 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) In February 1999, Tosco advanced three off-site cone penetrometers (CPT1 through CPT3) and drilled three off-site soil borings (68 through 1310) (ERI, March 2, 1999) In April 1999, Tosco installed nine off-site groundwater monitoring wells MW-8S, I, and D through MW-10S, I, and D) consisting of three nested wells (shallow, intermediate, and deep) at each of three well locations (ERI, June 9, 1999) In May 1999, ERI submitted a report entitled Air Sparge/Soil Vapor Extraction (ASISVE) Test, dated October 18, 1999, presenting the data collected during the ASISVE feasibility test In December 1999, 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 CAP as an Interim Remedial (IR) Action document During second quarter 2000, 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 MW-3 was also initiated 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 MW-3 and transported to the Tosco refinery for recycling during interim groundwater remediation efforts During June 2001, 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, ERI submitted an additional CAP The CAP included recommendations to install a microsparge system to remediate methyl tertiary butyl ether (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 12 on-site AS wells (AS1 through AS5, AS7, AS8, AS10, and nested wells AS-6SID and AS-9S/D), three on-site, single-casing groundwater monitoring wells (MW-1 through MW-3), four on-site, dual-casing groundwater monitoring wells (MW- • 4S/D through MW-7S/D), one on-site UST cavity well, and nine off-site groundwater 5886 3Q2005 QSSR doc SECOR International Incorporated