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SECTION 3.0 SUMMARY OF PREVIOUS INVESTIGATIONS 3.1 PREVIOUS SOIL INVESTIGATIONS Environmental investigations have been performed at Stockton Yard since 1988 Historical soil analytical results are summarized in Tables 3-1 and 3-2 A summary of the previous soil investigations is discussed below * On December 20, 1988, NDE Technology, Inc reported that a p leak had been detected on December 2, 1988 at the Stockton Yard from a 10,000 gallon underground storage tank (UST) containing 9,700 gallons of unleaded gasoline (NDE, 1988) • A 10,000-gallon gasoline UST, a 5,000-gallon diesel UST, and two pump islands and the associated product piping were removed in December 1989 through January 1990 Concentrations of TPH were detected in soil samples obtained during the tank excavations Analytical testing results detected TPH-g and. diesel (TPH-d) at concentrations up to 2,000 milligrams per kilograms (mg/kg) and 58 mg/kg, respectively BTEX was detected at concentrations up to 120 mg/kg The maximum TPH-g concentration was detected in a post- excavation soil sample that was collected at a depth of 14 feet bgs, below the fill riser end (west end) of the former gasoline UST (GEOCON, 1996x) • In 1992, Alton Geoscience (Alton) performed a preliminary site investigation at the Stockton Yard In March 1992, Alton drilled five soil bonngs, two for soil characterization (SB-1 and SB-2) and three for monitoring wells (MW-1 through MW-3) The monitoring wells were installed as 4-inch diameter wells, screened between 63 and 78 feet bgs Groundwater was encountered at approximately 65 to 68 feet bgs Concentrations of TPH-g were detected in soil samples collected at 46 feet bgs from borings SB-1 (120 mg/kg), well MW-2 (1 0 mg/kg), and well MW-3 (30 mg/kg) Benzene was detected in soil samples collected from ' each bonng at depths ranging from 35 bgs to the capillary fringe at 66 feet bgs The highest BTEX concentrations were detected in boring SB-1 at 46 feet bgs (benzene = 0 69 mg/kg, toluene = 5 2 mg/kg, ethylbenzene = 2 1 mg/kg, and total xylenes = 13 mg/kg) • Between April 1995 and January 1996, GEOCON drilled 12 soil borings, one for soil characterization (SB-3), nine for monitoring wells (MW-4 through MW-12), and two for vapor monitoring (VW-1 and VW-2) The vapor monitoring wells were installed as 4-inch diameter wells, screened between 15 and 70 feet bgs The groundwater monitoring wells were installed as 4-inch diameter wells screened between 60 and 80 feet bgs. Groundwater was encountered at approximately 61 to 62 feet bgs A total of 171 soil samples were collected and analyzed for TPH-g, TPH-d BTEX, and MTBE MTBE was not detected in any soil samples TPH-d was detected in only one soil sample, identified as MW5-9, collected from well MW-5 at 45 feet bgs at a concentration of 12 mg/kg Concentrations of S IPROJI41040100041SYYARDIMAINTYARDSkDOC 'j»l uRS Greiner woadmrd Clyde M