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i to r i c• ERT 205513 QSR18 Tosco Service Station 5886 Stockton Califorma October 25 2001 • 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 Currently, there are three on-site, single-casing groundwater monitoring wells (MW1 through MW3), four on-site, dual-casing groundwater monitoring wells (MW4SID through MW7SID), one on-site UST cavity well, and nine off-site groundwater monitormg wells (MW8SII/D through MWIOSII/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 THIRD 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 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 • Approximately 54,500 gallons of MTBE impacted groundwater were purged from beneath the site and transported to the Tosca refinery for disposal Approximately 216,000 gallons of groundwater have been purged from beneath the site since IR activities were initiated In June 2000 • Tosco, subcontracted with Gettler-Ryan, Inc (GRI) to seal surface cracks on the site • 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 monitormg and sampling at the site on August 20 and 21, 2001 The GRI Third Quarter 2001 Groundwater Monitoring and Sampling Report is provided as Attachment A The results of the third quarter monitormg and sampling event indicate the following • Groundwater was measured at approximately 6 7 to 10 0 feet below ground surface (bgs) in the groundwater monitoring wells (an elevation variation of approximately 0 3 to 1 2 feet when compared to the second quarter 2001 groundwater monitormg and sampling event) 3