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ameO level data from monitoring wells formerly present in the eastern portion of the Tracy Rail Yard, north of the Off Site South Area (ARCADIS, 2008). This groundwater flow direction is consistent with information from nearby sites associated with the HPP (TAOC Tracy Pump Station and Alden Park; Geomatrix, 2006). 2.3 PREVIOUS INVESTIGATIONS Geocon, Kennedy/Jenks, ARCADIS, on behalf of UPRR, and AMEC, on behalf of CEMC, conducted soil and groundwater investigations in the southern portion of the Tracy Rail Yard site between 2005 and the present (Geocon, 2005; Kennedy/Jenks, 2006; ARCADIS, 2008; and AMEC, 2010). Soil and groundwater sampling locations and petroleum hydrocarbon analytical results from these past investigations are shown on Figures 3 through 6. Analytical results from these past investigations for borings along the southern boundary of the Tracy Rail Yard site, and borings in the Off Site South Area, are included in Appendix A. 2.3.1 Southern Portion of Tracy Rail Yard During previous investigations, Kennedy/Jenks and AMEC observed evidence of petroleum- affected soil, and elevated concentrations of total petroleum hydrocarbons (TPH) were detected in soil samples from several borings (Figure 3) at depths up to 20 feet bgs in the vicinity of the former TAOC pipeline along the southern boundary of the Rail Yard. Elevated concentrations of TPH were detected in several groundwater samples in the vicinity and downgradient (north) of the former TAOC pipeline (Figure 4). Benzene was detected at concentrations of 0.0005 and 0.007 milligrams per kilogram (mg/kg) in the soil samples collected from boring TRY-11 at 6.0 feet bgs and boring TRY-16 at 5.5 feet bgs, respectively(Figure 3). These concentrations were J-flagged as they were reported between the laboratory method detection limit and the laboratory reporting limit. Toluene, ethylbenzene, and xylenes were detected at concentrations of 3.6, 12, and 9.1 mg/kg, respectively, in the sample collected from boring G-B8-OU3 at 20 feet bgs. Benzene, toluene, ethylbenzene and xylenes (collectively referred to as BTEX) were not detected in any other soil samples collected along the southern boundary of the Rail Yard. BTEX was not detected in groundwater samples collected along the southern boundary of Tracy Rail Yard site (Figure 4). Volatile organic compounds (VOCs)were detected at low concentrations in three soil samples collected along the southern boundary of Rail Yard in 2005 and 2006 by Geocon and Kennedy/Jenks. Detected VOCs include isopropyl benzene, n-propyl benzene, sec- butylbenzene, naphthalene, acetone, and tetrachloroethene (PCE). Acetone and PCE are not associated with the HPP. VOCs were not detected in groundwater samples collected in 2005 and 2006 along the southern boundary of the Tracy Rail Yard site with one exception. AMEC Geomatrix, Inc. X:\16000s\161140\4000 REGULATORY\South WP 063011\1 txt,curs, Itrs\Text.docx 3