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i' A S 5 0 C I A T E S I N c 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 contairung 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 (SB 1 through SB 8) 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 Mumcipal 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 QUARTERLY MONITORING ACTIVITIES ATC performed quarterly groundwater monitoring and sampling on September 29, 1998 Field work included measuring the depth-to-water in wells MW 1 through MW6 and purging and sampling the water from these wells in addition to the nearby Thornton No 2 Municipal Supply Well (Supply Well) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Additionally, at the request of PHSIEHD staff, additional water samples were collected from monitoring wells MW 1 through MW6 and analyzed for dissolved oxygen toDepth to water measurements were collected on September 29, 1998 from monitoring wells MW 1 through MW6 The water table elevation has risen an average of 5 07 feet in the w 19432"uanlyl2gr-1998 dw 2