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ERI 205513 QSR19 Tosco Service Station 5886,Stockton,,Califonua January 30,2002 . 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 three on-site, single-casing groundwater monitoring wells (MWI 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 (MWBS/I/D through MWIOS/I/D) consisting of three wells at each nested well location as shown on Plate 2 The purpose of these wells is to evaluate the lateral and vertical extent of dissolved hydrocarbons detected in groundwater beneath the site Based upon data collected during ongoing quarterly groundwater monitoring and sampling, dissolved hydrocarbons are delineated both laterally and vertically in the vicinity of the site However, dissolved hydrocarbons continue to be detected in groundwater samples from beneath the site and are concentrated in the vicinity and downgradient of the UST cavity FOURTH 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 fourth quarter 2001 • The County approved installation of a micosparge system to remediate MTBE-impacted groundwater beneath the site in a letter dated October 2, 2001 • The County approved discontinuing laboratory analysis of groundwater samples for total petroleum hydrocarbons as diesel (TPHd) in their letter dated November 6, 2002 • ERI submitted a well installation permit to the County to install eight single-completion and two dual-completion microsparge wells at the subject site • Approximately 54,500 gallons of MTBE-impacted groundwater were purged from beneath the site and transported to the Tosco refinery for disposal Approximately 265,000 gallons of groundwater have been purged from beneath the site since IR activities were initiated in June 2000 • GRI of Dublin, California, under direct contract to Tosco, collected monthly groundwater samples from on-site wells MWI through MW4D/MW4S and MW6D/MW6S for MTBE analysis and performed quarterly groundwater monitoring and sampling at the site on November 19 and 20, • 3