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Historical Summary <br /> LANGSTON'S MARKET <br /> 15615 South 7"Street,Lathrop,California <br /> June 1990 A 4,000-gallon UST failed at Langston's Market following a helium pressure test and <br /> 1,200 gallons of unleaded gasoline was released. <br /> April 1992 Murray and Associates manually drilled eight 2-inch diameter soil borings to a depth <br /> of 17 feet(ground water between 17-18 feet). Found that soil contamination in the <br /> vicinity of the former UST extended down to capillary fringe zone and water table, <br /> with little lateral spreading. SB-4 about 2.5 feet west of UST pit detected 14 <br /> milligrams per kilogram(mg/kg)petroleum hydrocarbons at 14 feet and 7 mg/kg at <br /> 17 feet. SB-8 about 33 feet NW was non-detect. <br /> April 1993 Installation of four ground watermonitoringwells at the site.Soil contamination was <br /> verified to exist from 15 feet below bsg to below ground water. Benzene <br /> concentrations in ground water samples up to 17,000 micrograms per liter(µg(1). <br /> Sept. 1994 Benzene concentrations up to 31,000µg/1 in groundwater. <br /> Dec. 1994 San Joaquin County Environmental Health Department (EHD) approved as an <br /> interim remediation activity a Remedial Excavation Work Plan to excavate 3,000 <br /> tons of soil. <br /> July 1995 After an asbestos survey, removal of surface structures and the four ground water <br /> monitoring wells by SEMCO. <br /> Aug. 1995 Pothole trenching by WHF Environmental to delineate the extent of contamination <br /> failed due to sandy soil;WHF was given approval to proceed with excavation of the <br /> former tank pit area. <br /> Sept. 1995 Sidewalls and bottom of the excavated area sampled by WHF. Soil samples to north <br /> and west show small amounts of contamination remaining under 50 mg/kg. <br /> Excavation was limited to the east and south by roadways and utilities; remaining <br /> contamination in those directions were less than 100 mg/kg. <br /> Sept. 1995 WHF and Frontier Drilling conducted six soil borings and completed four as ground <br /> water monitoring wells. Borings terminated between 34-35.5 feet after sampling <br /> below a clay interval between 27-33 feet.EW-1(MW-1)and MW-2 are 4-inch wells <br /> that can be used for limited ground water extraction. The wells were surveyed by a <br /> State-licensed surveyor. <br /> Ad. ,d GenEmiranm nl84 Ina <br />