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1 I FFsr Work Plan For Additional Groundwater Delineation and Ozone Microsparge system Installation,Tosco(Former BP)Station No.11195 September 19,2002 SITE DESCRIPTION The subject site is situated immediately east of the Louise Avenue off-ramp of Interstate 5 at the southwest corner of East Louise Avenue and Harlan Road in Lathrop, California (Figure 1). Current station facilities include two 12,000-gallon double-wall gasoline USTs, two dispenser islands, related product lines, one canopy, and a station building. Former station facilities removed during construction activities performed in December 1998 and January 1999 included one 10,000-gallon, one 8,000-gallon, and one 6,000-gallon single-wall fiberglass gasoline USTs, two dispenser islands,related product lines, and two canopies. Seven onsite groundwater monitoring wells (MW-1 through MW-6 and MW-10) and nine offsite groundwater monitoring wells (MW-8 and MW-9 plus MW-11 through MW-17) are present at and in the site vicinity. Monitoring well MW-7 was properly destroyed in 1998. In addition, three temporary groundwater extraction conductor casings were installed at the site, one in the former UST pit and two in the new UST pit, prior to backfilling. The locations of pertinent site features are shown on Figure 2. As an earlier interim remedial measure, Tosco has been routinely extracting groundwater from the conductor casing in the former UST pit and selected monitoring wells since January of 1999. GROUNDWATER MONITORING WELL INSTALLATION To further evaluate groundwater conditions downgradient of the site, GR proposes the installation of three offsite groundwater monitoring wells at the locations shown on Figure 2. GR Field Methods and Procedures are included in Appendix A. To complete the proposed scope of work, GR proposes the following tasks: Task L Pre-Field Activities GR will update the site-specific safety plan and obtain the necessary well installation permits from the EHD. An encroachment permit will be Icquired from the City of Lathrop. The proposed well locations will be marked and a private utility locator will be contracted to locate any underground utilities near the proposed drilling locations. Underground Service Alert(USA)will be notified a minimum of 48 hours prior to drilling. Task 2. Monitoring Well Installation GR will oversee the installation three offsite groundwater monitoring wells at the locations shown on Figure 2. A California licensed well driller will install the wells. A GR geologist will observe the drilling activities and prepare logs of the well borings. Prior to drilling, the boreholes will be hand excavated to 5 feet bgs to confirm that the locations are clear of underground utilities. The well borings will be advanced to approximately 20 feet bgs with 8-inch-diameter hollow-stem augers. 140193.14 2