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1.2 2017 High Resolution Site Characterization 1.2.1 Background In response to the conclusions reached at the meeting, Kennedy/Jenks conducted a file review and developed the High Resolution Site Characterization (HRSC) Work Plan dated 31 March 2016 (Kennedy/Jenks 2016). The file review yielded documents describing five underground storage tanks (USTs) associated with past fueling operations that were located at the Site. Reportedly, two tanks stored diesel fuel, one stored wastewater from the diesel fueling service, and two stored gasoline. The first diesel tank (located near the existing sand tower) was a UST with a capacity of 26,000 gallons; was reportedly constructed out of railcars welded together; was installed in 1949; and was removed in 1990. The wastewater tank was a buried tank car with a capacity of 10,000 gallons; was installed in 1976; and was also removed in 1990. The wastewater was routed from the fueling area to the wastewater tank near the mechanic's shop. One gasoline tank was a UST with a capacity of 2,000 gallons, installed in 1974 and removed in 1990. The other gasoline tank was an aboveground 55-gallon drum. The former locations of the larger tanks (26,000-gallon diesel, 10,000-gallon wastewater, and 2,000-gallon gasoline) were provided in the 1991 tank closure report and are shown on Figure 2. According to the reviewed documents, post-removal sampling in the side-walls and bottom of the excavation of the 26,000-gallon UST found residual soil impacts. The samples from the 26,000-gallon diesel UST area, the remote fill line area, and the associated stockpile found total extractable hydrocarbons (TEH) at concentrations up to 5,100 milligrams per kilogram (mg/kg). Samples from the 2,000-gallon gasoline UST area detected total petroleum hydrocarbons- gasoline (TPHg) at 1.4 mg/kg. The extent of the excavations based on the San Joaquin County Public Health Services (SJCPHS) case closure summary (1996) is shown on Figure 2. The excavation at the former 26,000-gallon diesel tank consisted of a narrow, 20-foot-deep pit (presumably under the tank) surrounded by a larger 250-foot by 50-foot by 6-foot-deep excavation. The excavation under the 10,000-gallon wastewater tank consisted of dimensions of 40-foot by 12-foot by 9-feet deep. Based upon the file review, the HRSC consisted of a total of 15 LIF borings drilled along four transects. The boring locations were arranged around the former USTs, and upgradient and downgradient of the 26,000-gallon diesel UST The LIF probe detects the presence of petroleum constituents by utilizing ultraviolet light generated by a laser and transmitted to the subsurface through a fiber optic cable and sapphire window. The tooling also included a paired electroconductivity probe. Soil conductivity, in general, varies with grain size. 1.2.2 HRSC Summary The HRSC findings are presented in Kennedy/Jenks (2017). In summary, the LIF data indicated that hydrocarbons as light non-aqueous phase liquid (LNAPL) were present in LIF#4. LIF#4 is located slightly northwest (downgradient) of the former 26,000-gallon diesel UST. It is likely the Additional Soil and Groundwater Sampling Work Plan, BNSF Mormon Yard, Stockton CA Page 2 Myybrisf2thnstwo\wp12018 1899020.00_mormon_yard1work_plan_d12018 mormon yard sampling wp_mwm.doc