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Work Plan for Sail Excavation 2 The Southland Corporation,Store#24304 455 Grant Line Road CA January 26 1998 underground storage tanks(USTs)and associated piping located In the center of the site On October 27,1986,the USTs were taken permanently out of service after a tank failed a leak test From December 1986 to September 1988,Harding Lawson Associates(HLA)drilled borings for Installation of mondonng wells MW-1 through MW-15, and exploratory probes P-1 through P-7(Plate 2, Attachment 1) Highest total petroleum hydrocarbons-as-gasoline(TPH-G) concentrations in sod were detected in boring P-4 at 4 7 feet BGS at 1,400 milligrams per kilogram (mg/kg),and highest benzene was detected in P-8 at 98 mg/kg (Table 1,Attachment 2) In 1990, HLA proposed the installation of a sod vapor and groundwater extraction system They conducted a short-term pump test which indicated well yields ranging from 20 to 40 gallons per minute On May 11, 1993, Groundwater Technology, Inc installed one groundwater extraction well (GWE-1) Benzene and TPH-G were detected in the boring for the well at 2 7 mglkg,and 280 mgfkg, respectively,at 8 feet BGS A discharge line was installed from the remediation system to the storm drain in June 1995 pnor to installing the remediation system equipment in September 1995 Groundwater extraction from GWE-1 began in October 1995 The system was shut off in April 1996 because of low yield and inability to lower the water table MIn October 1996,wells GWE-2 and GWE-3 were installed In vaults along with lateral piping to the remediation system Benzene and TPH-G were detected in the sod boring for well GWE-3, at 3 7 mg/kg and 2,000 mg/kg, respectively,at 5 feet BGS Quarterly groundwater monitoring and sampting of the sde-related wells has occurred since July 1988 Benzene and TPH-G concentrations have decreased from 28,000 micrograms per liter(Ug/L)to 12,000 pg/L and 100,000 pg/L to 52,000 pg/L,respectively Hydrogeology " Tracy is located in the northwestern part of the San Joaquin Valley,California,a broad asymmetric trough filled with Cretaceous and Cenozoic sediments The Quaternary sediments in the Tracy area,were derived from the Coast Ranges to the west The site is situated at approximately 25 feet above mean sea level on a distal northern part of an alluvial fan The shallow groundwater at the site shows seasonal fluctuation from approximately 3 to 6 feet BGS TASK 1: SITE SPECIFIC HEALTH AND SAFETY PLAN The existing site-specific health and safety plan will be revised to include any new safety concerns as required by the Occupational Safety and Health Administration (OSHA)guidelines(29 CFRJ910.120) W5eNKP LTR SOUTHLAND FLUOR DANIEL GTI