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t . U stagy Work Plan to Destroy Existing Monitoring and Remedial Wells 76 Station No.5886 April 18,2011 - investigation in order to estimate methyl tertiary butyl ether (MTBE) concentrations in' groundwater. In February 1999, Tosco advanced three off-site cone penetrometers (CPT1 through CPT3) and. drilled three off-site soil borings(68 through B10). In April 1999, Tosco installed nine off-site groundwater monitoring wells, MW-8S/1/D through` MW-10S/I/D, consisting of three nested wells (shallow, intermediate, and deep) at each of three' well locations. In May 1999, ERI performed an Air Sparge/Soil Vapor Extraction (AS/SVE) feasibility test and subsequently submitted a report entitled Air Sparge/Soil Vapor Extraction(AS/SVE) Test, dated October 18, 1999, presenting the data collected during the AS/SVE 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 (SJCPHD) dated February 22, 2000, approving the remediation recommendations provided in ERI'S CAP as an Interim' Remedial Action document. During the second quarter 2000, ERI installed one-UST cavity well in general accordance with the CAP. 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 the third quarter 2000, pending clarification from SJCPHD regarding water sampling and data collection requirements. Purging was resumed during January 2001 and continued through January 2002, when it was terminated due to the subsequent installation and start-up of an ozone sparge (OS) remediation system. In total, 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 the underground storage systems to evaluate system integrity. According to Tosco, the results of the enhanced detection test indicated that the underground storage systems were functioning within acceptable parameters. During third quarter 2001, ERI submitted an additional CAP. The CAP included recommendations to install an OS system to remediate MTBE-impacted groundwater beneath,' the site. In January 2002, ERI oversaw the installation of on-site sparge wells AS-1 through AS-5, AS-7, AS-8, AS-10, and nested wells AS-6S/D and AS-9S/D. Currently, there are 12 on-site sparge wells (AS-1 through AS-5, AS-7,AS-8, AS-10, and dual- completion wells AS-6S/D and AS-9S/D), three on-site, single-casing groundwater monitoring wells (MW-1 through MW-3); four on-site, dual-completion groundwater monitoring wells (MW 4S/D through MW-7S/D), one on-site UST cavity well, and three off-site groundwater monitoring well clusters(MW-8S/I/D through MW-10S/1/D). 2 - i .