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Additional Soil and Grouht(water Investigation Report California Central Traction Company, 1645 Cherokee Lane, Stockton,CA September 22, 2oo8 Page 2 During the excavation activities performed in 2005, groundwater was encountered in the excavation at approximately 75 fbg. The groundwater flow direction has been estimated to be toward the northeast. 4.0 SITE BACKGROUND January 26, 1999: One 1,000-gallon diesel and one 6,000-gallon gasoline underground storage tank(UST) were previously maintained on site for an unknown period of time and were removed from the site by Thorpe Oil Company in January 1999. One soil sample, collected from the diesel tank excavation at 9 feet below grade (fbg) contained 8,000 milligrams per kilogram (mg/kg) total petroleum hydrocarbons as diesel (TPH-d) (Hydro-Environ mental Technologies, Inc. (HETI) 2004). August 2-3, 1999: Five soil borings (B-1 through B-5)were drilled to a maximum depth of 56.5 fbg. TPH-d was detected in 14 of the 28 soil samples collected at depths ranging from 10 to 55.5 fbg. The maximum TPH-d concentration was detected in the sample collected from B-1 at 10 fbg at a concentration of 22,000 mg/kg. TPH-d was detected at 94,000 micrograms per liter (µg/1) in the grab groundwater sample collected from B-1, which was the only groundwater sample collected during this investigation (URSGWC 1999)• These analytical results are included in tabular form in Appendix A1. The locations of these borings are show on Figure 3. July 12, 2000: HETI drilled six soil borings (B-1 through B-6) to total depths of 50 fbg. Grab groundwater samples were collected each of these borings. Analytical results for all soil and grab groundwater samples for total petroleum hydrocarbons as gasoline (TPH-g), TPH-d, BTEX constituents, and five oxygenates were all below reported laboratory limits (HETI 2001). The locations of these borings are show on Figure 3. August 28-29, 2000: HETI constructed three groundwater monitoring wells(MW-1, MW-2, and MW-3) to 50 fbg with 15 feet of screen (Figure 3). Soil samples were not collected for analysis from wells MW-1, MW-2, and MW-3 due to the close proximity of previously installed borings B-1, B-4, and B-5, respectiVely. Soil analytical data from borings B-1, B-4, and B-5 are available in Appendix Al. TPH-d was detected in groundwater samples collected from each of the three wells. Quarterly monitoring was initiated in September 2000 (HETI 2001), and continued through February 2002. The wells were dry during both the November 2001 and -- February 2002 monitoring events (HETI 2004). Groundwater data collected from these wells are included in Table 1. These were subsequently destroyed in 2005 in preparation for site excavation activities. August 20, 2001: HETI installed an additional groundwater monitoring well (MW-4) in the former diesel UST excavation (HETI 2004). June 2004: HETI advanced five additional soil borings (B-7 through B-11) to total depth of 50 fbg. All analytical results for TPH-g and BTEX constituents were below laboratory reporting limits. TPH-d was detected in soil samples at a maximum concentration of 4,300 mg/kg in the sample collected at 25 fbg from B-11. Soil analytical results are included in tabular form in Appendix A2. TPH-d was detected in two grab groundwater samples at a maximum concentration of 2,900 micrograms per liter(µg/L) in the sample collected from B-8 (HETI 2004). These data are included in Table 1.