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(VYATC � . ASSOCIATE S INC correspondence dated July 7, 1994 A required demolition asbestos survey conducted previously on the station building, determined the presence of asbestos containing materials E T Abatement, of Modesto, California, properly removed and disposed of the site's suspected asbestos containing materials on November 11, 1994 In February 1995, Smith Technology personnel supervised the excavation of approximately 1,400 cubic yards of soil from the vicinity of the former underground storage tanks Approximately 10,000 gallons of groundwater was pumped from the open excavation into an on- site Baker Tank The excavation pit was subsequently backfilled with imported self-compacting material Excavation activities are discussed in detail in Smith Technology's Excavation Summary Report, dated October 24, 1995 On November 26 and 27, 1996, a total of eight soil borings (SB1 through S138) were advanced to depths ranging from approximately 20 5 to 45 5 feet bgs under the supervision of Smith Technology The distribution of residual TPHg and benzene in soil beneath the site is generally between 11 and 30 feet bgs and extends approximately 70 feet from north of the former UST excavation near the Thornton Municipal Supply Well No 2 (the Supply Well) compound and associated underground water lines The results of the November 1996 investigation is summarized in Smith Technology's aforementioned Problem Assessment Report - Interim Remedial Plan dated September 4, 1997 On December 2, 1996, Smith Technology personnel began the construction of a soil aeration cell in accordance with a letter workplan submitted to PHS/EHD and an authority to construct issued by the San Joaquin Valley Unified Air Pollution Control District Approximately 1,200 cubic yards of stockpiled soil was placed on visquene plastic, with a maximum soil height of three feet, to promote aeration of the hydrocarbon impacted soil On March 24, 1997, soil samples were collected from the on-site soil aeration cell to monitor the progress of soil remediation Four soil samples were collected for every 100 cubic yards of soil and were composited in the laboratory at a 4 1 ratio Soil samples were placed on ice and transported under chain-of-custody to Argon Laboratories, in Ceres, California Samples were analyzed for TPHg and BTEX No soil samples contained TPHg or BTEX at concentrations above laboratory detection limits Smith Technology submitted a Problem Assessment Report - Interim Remedial Plan (Plan) dated September 4, 1997 The Plan recommended that a pilot scale test of soil vapor extraction and air sparge be implemented to determine the effectiveness of these methods as a remedial option To implement the pilot scale test the Plan proposed to install three vapor extraction wells, one air sparge well, and a sentinel monitoring well It was proposed that the sentential monitoring well be nested to evaluate the vertical migration of contaminants San Joaquin County Public Health Services, Environmental Health Division PHS/EHD correspondence dated September 22, 1997 concurred with the Plan's recommendations Pre- w 1625821quaA1y13gr-1999 doe 2