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Kennedy/Jenks Consultants ESI (1991) describes the removal of three tanks, above grade diesel fuel dispenser piping, a fill line, and results of post-removal sampling completed in 1990. The approximate layout of the former USTs, fill line, wastewater line, and inspection pit from the ESI (1991) report is shown on Figure 2. The 2,000-gallon gasoline UST was located near the mechanical shop. The 10,000-gallon wastewater tank was located south of the tracks along what is currently a parking lot along the east-west portion of Diamond Street. The 26,000-gallon diesel tank was located alongside the former/current sand tower. The fill line extended from the diesel UST southeast under the tracks to Worth Street. The wastewater line is shown to have extended from the diesel UST to the wastewater tank with two drain lines entering the wastewater line from a former inspection pit. The wastewater line reportedly failed an integrity test in 1990 and was left in place with the recommendation that additional characterization along the drain line be conducted. Per ESI (1991), post-removal sampling in the former equipment cavities found residual soil impacts such that "additional soils investigation and removal activities were completed and a final report (was) being prepared." The additional investigation and removal report referenced was not found during review of BNSF files. The 1990 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 (TPH-G) at 1.4 mg/kg. The stockpile sample from the 10,000-gallon wastewater UST area had a TEH concentration of 22 mg/kg and a polychlorinated biphenyl (PCB) detection of 0.095 mg/kg of analyte Aroclor 1254; in situ samples from the wastewater UST area did not detect TEH, TPH-G, or PCBs. By January 1996, additional investigation and removal was apparently completed as reported in the SJPHS (1996) case closure summary. SJPHS (1996) presents dimensions of all completed removal excavations at the Site but did not include a figure or years during which the removal activities were completed. The interpreted extents of the excavations based on SJPHS (1996) are 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 250-foot by 50-foot by 6-foot-deep excavation. Under the 10,000-gallon wastewater tank, the pit was 40 feet by 12 feet by 9 feet deep. The wastewater line was reportedly ultimately grouted and decommissioned in place. 2.4 Site Background Findings to Inform HRSC Plan Based on the above described background information, Third Quarter 2015 Monitoring Report, Diamond Foods, Inc. for the Diamond Foods hexavalent chromium site, the First Quarter 2015 (Biennial) Groundwater Monitoring Report for the San Joaquin County Public Works Department site, and an EDR of the area around and including the Site, the following information is used to inform the HRSC plan presented in Section 3.0: High Resolution Site Characterization Work Plan, BNSF Mormon Yard, Stockton, California Page 4 g:lis-groupdminljob11311365020.01_bnsf109-reports1hrsc-wkpin1text.doc