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• ATTACHMENT A SITE INVESTIGATION HISTORY The Chevron Banta Terminal is located approximately 5 miles east of Tracy, in the agricultural community of Banta, California The active fuel terminal on site has been in operation since 1966, and consists of nine aboveground fuel storage tanks, tank-truck loading racks, above- and below-ground piping, and an office The tank farm is enclosed by a 3-foot high secondary containment berm A portion of this berm forms a spill containment area located in the northern portion of the terminal Fuel lines from the fuel storage tanks run above ground within the secondary containment area The fuel lines run below ground between the secondary containment area and the tank-truck loading racks under the paved portion of the terminal (Plate 1) The San Joaquin Groundwater Basin underlies the site • Beneficial uses of groundwater in the area include municipal, domestic, irrigation, stock watering, process, and service supply i Four spills have been documented at the site The first spill occurred on June 9, 1984 and consisted of 13,000 gallons of gasoline, diesel and heating oil Soil was excavated immediately after the spill in the spill area until no subjective evidence of hydrocarbons remained The second spill was a tank overflow in August 1990 consisting of approximately 300 gallons of gasoline The third spill occurred in August 1998, when an unknown volume of gasoline was released as a result of overfilling tank T-137 In November 1999, an unknown quantity of red dye diesel was released from a tanker overfill at the loading racks Since December 1983, 23 monitoring wells (MW-1 through MW-23) and three piezometers (T-1 through T-3) have been installed at the site Well T-2 has since been destroyed and well MW-9 has been inaccessible since 1992 With the exception of four wells, all are constructed to monitor the shallow water-bearing zone to depths of 25 to 30 feet bgs Four wells (MW- 12, MW-13, MW-22, and MW-23) were constructed to monitor a Iower water-bearing zone at an approximate depth of approximately 48 feet bgs Geraghty & Miller, Inc (G&M) performed a site assessment in August 1993 Twenty soil borings were drilled in the farm field adjacent to the site Groundwater samples collected i