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QUARTERLY SUMMARY REPORT ��'-_ C V U First Quarter 2003 A p R 16 2003 (January- March) ENVIRORMENT HEALTH PERMIT/SERVICES TOSCO (76) Service Station No. 11195 16500 South Interstate 5 Lathrop, CA CITY: Lathrop COUNTY: San Joaquin BACKGROUND: • The site contains an operating 76 service station. Five groundwater monitoring wells were installed in December 1992. Two additional monitoring wells were installed in September 1993. In July 1998, one waste oil underground storage tank (UST) and the associated remote fill piping were removed from the site. Approximately 10 cubic yards of soil were removed from the site and disposed of at an approved landfill. An abandoned domestic well was sampled and properly destroyed in July 1998. In September 1998,one monitoring well was destroyed and five monitoring wells were installed in the vicinity of the site. Sensitive receptor and water well surveys have been performed for the site. In December 1998 and January 1999,three fuel USTs were removed from the site during UST replacement activities. Approximately 1,017.96 tons of soil and backfill materials were removed from the site and disposed of in an approved landfill. A slotted temporary conductor casing was installed in the former UST pit to facilitate removal of hydrocarbon-impacted groundwater. Subsequently, periodic groundwater purging began January 2000. In May 1999 Tosco Marketing Company assumed responsibility for investigative and remedial activities at the site from British Petroleum (BP). Submitted Interim Remedial Action Plan in July 1999. In February 2002,five offsite geoprobe soil borings were advanced downgradient of the subject site. Five offsite Groundwater Monitoring Wells were installed in May 2002. Four offsite monitoring wells were installed in December 2002. In December 2002, an Ozone Microsparge Interim Remedial System was installed using ten onsite sparge points and five offsite sparge points. The twenty monitoring wells are currently sampled on a quarterly basis. Corrective Action Plan(dated August 28, 2002) submitted. RECENT QUARTER ACTIVITIES: • Monitored and sampled the existing wells. • Prepared and submitted the quarterly summary report. • Purged a total of 35,000 gallons of groundwater from the conductor casing CC-1, monitoring wells MW-3, MW-5 and MW-10 during 7 weekly purging events from January 6 through February 18, 2003. ANTICIPATED NEXT QUARTER ACTIVITIES: • Monitor and sample groundwater monitoring wells. • Prepare and submit the quarterly summary report. • Perform monthly system maintenance and sampling of selected wells (MW-3 and MW-10). • Submit Groundwater Monitoring Well Installation and Ozone Microsparge System Installation and Startup Report. • Re-issue updated potentiometric maps from the most recent three QMR reports with corrected information. i 140193.1 1