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ERI 205513 05820 Tosco Service Station 5886, Stockton,California _ April 25,2002 �. gallons of groundwater during second and third quarters 2000 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 • 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 Corrective Action Plan (CAP), dated September 25, 2001 The CAP included recommendations to install a micosparge system to remediate MTBE impacted groundwater beneath the site Currently, there are ten on-site AS wells (ASI through AS5, AS7, AS8, and AS10, 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/I/D through MW IOS/I/D) consisting of three wells at each nested well location as shown on Plate 2 and the New Construction Site Plan (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 form on- site wells and are concentrated in the vicinity and downgradient of the UST cavity FIRST 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 first quarter 2002 • ERI observed installation of ten AS wells (AS1 through AS5, AS7, AS8, and AS 10, and nested AS wells AS6S/D and AS9S/D) The locations of the wells are shown on Plate 3 • Global Project Management Services, Inc (GPMSI), under direct contract to Tosco, installed the groundwater remediation system at the subject site The groundwater remediation system consists of a K-V Associates, Inc (KVA) "C-Sparge"r"' ozone microsparging system The system uses 12 KVA Spargepoint® wells (ASI through AS5, AS7, AS8, AS 10, AS6S/D and AS9S/D)with piping connected to a "C-Sparge"TM panel consisting of an ozone generator, air compressor, and programmable timer/controller • In February 2002, the remediation system was activated and ERI initiated monthly operation and maintenance (O&M) of the system • Approximately 15,000 gallons of MTBE-impacted groundwater were purged from beneath the site and transported to the Tosco refinery for disposal Approximately 280,000 gallons of groundwater have been purged from beneath the site since IR activities were initiated in June 2000 3