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R .J 1.0 SITE LOCATION AND DESCRIPTION The JC Trucking property is located in the southern section of the city of Stockton, San Joaquin County, California, between Jackson Street on the north, Clay Street on the south, '- and South Aurora Street on the east (Figure 1). Private residences border the property to the west, and commercial enterprises are predominant to the north and east. The property presently consists of an unpaved rectangular lot with a 50 X 30 foot concrete slab at its northeast corner, the site of the former office building, and a four foot high 100 X 40 foot foundation for the former loading dock situated along the center of the east La side of the property. The site was formerly a truck terminal and was closed in February 1991, after a fire. Two 3000-gallon underground gasoline storage tanks were located in the northwest corner and two 3000 gallon underground diesel storage tanks were located in northeastern corner of the site, The two former tank location sites are indicated by depressions in the ground surface. Figure 2 shows the location of the tank pits. The property is presently rented for truck maintenance and storage. 2.0 PROJECT HISTORY In May 1992, the underground storage tanks (USTs) were removed and one soil sample was +� taken from each stockpile of soil, and four soil samples were taken from each tank pit. The tank pits were backfilled with clean soil. 4.0 On March 9, 1994, San Joaquin County Environmental Health Division (SJCEHD) notified JC Trucking that a preliminary site assessment was necessary. On January 1996, Aqua Geosciences Inc. (AGI) submitted a work plan. The plan was approved with modifications on L. March 27, 1996. In August 1997, AGI investigated the site and collected soil and grab water samples from nine borings in the vicinity of the former gasoline tank location and the former diesel tank location. Analytical results found gasoline in the soil at low concentrations and diesel at higher concentrations. Groundwater was impacted with high concentrations of both gasoline and diesel. 4 In January 1998, AGI prepared a Preliminary Investigation and Evaluation Report and submitted it to SJCEHD. In their report, AGI recommended further assessment of the 66 groundwater plume. On July 13, 1998, SJCEHD reviewed the report and required further soil and groundwater characterization. i• On August 8, 1998, a work plan was prepared for six monitoring wells. On October 2, 1998, SJCEHD approved the six monitoring wells requested in the work plan and required two additional monitoring wells to 70 feet below ground surface (bgs). In March and April of 1999, six monitoring wells and one deep soil boring were installed by JJW Geosciences (JJW). On August 30 and 31, 1999, two monitoring wells (MW-7 and MW-8) were installed to 110 feet bgs. 1 JJW GEOSCIENCES Inc.