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Additional Soil and Grounder Investigation Work Plan CCT Stockton Rail Yard, 1645 Cherokee Lane, Stockton,CA October 4, 2007 Page 4 Results from all soil and grab groundwater samples from boring B-6, installed in 200o, analyzed for TPH-g,TPH-d, BTEX constituents, and five oxygenates were below their respective laboratory limits. Based on historical soil data collected prior to excavation activities in 2005, and on the extent of the 2005 excavation, no apparent data gaps exist with respect to site soils. The excavation, which removed the vast majority of all previously investigated areas and approximately 10,400 tons of hydrocarbon-impacted soil from the site in late 2005, was documented in the RAR. After reviewing the RAR, the SJCEHD, in a letter dated May 14, 2007, requested that the responsible party"submit corrected and/or clarified data tables, and revised maps of the excavation with all sample locations identified and successive excavation margins shown." While representatives of TRC were not involved in the soil sampling and removal activities or the subsequent preparation of the RAR,TRC personnel did review all information presented in the RAR. The conflicting data concerning several of the soil samples identified by the SJCEHD in the May 14, 2007 letter remain problematic. Fortunately, these issues concern samples collected from locations that Nti ere subsequently excavated. The value of analytical results from sample locations that have been subsequently excavated are perhaps limited to profiling soil for disposal rather than identifying data gaps and directing any further site investigation. As with any environmental soil excavation, the only significant soil data is that obtained from confirmation sample locations around the maximum extent of the excavation, representing soil impacts that remain in place. During excavation activities, a total of 52 confirmation soil samples were collected between August 3o and October 13, 2005 for analysis to assess to what extent soil should be excavated. Based on a review of data provided in the RAR, the analytical results from the 52 confirmation soil samples were segregated into two tables. Analytical results for soil samples collected from locations which were subsequently excavated are presented in Table 2. Analytical results for soil samples collected from locations which remained in place'after excavation activities were completed are presented in Table 3. The locations-6f"tMie soil"samples collected from areas which were subsequently excavated out as well as the locations of samples which remained in place after excavation activities are presented on Figure 4, as is the approximate location and depth of the final excavation. Based on a review of all soil analytical data from confirmation samples collected from locations not removed during the excavation (Table 3), only one of the 39 confirmation samples collected reported concentrations of TPH-g and TPH-d that would warrant further investigation. Soil sample WWCSF-78, collected at the northern most extent of the excavation at a depth of 78 fbg, contained 6,000 mg/kg TPH-d and 2,800 mg/kg TPH-g. 4.2 Groundwater Data TPH-d, TPH-g, and benzene were detected in a historic grab groundwater sample collected from boring B-1 on August 2, 1999 by URSGWC at concentrations of 94,000 µg/1, 12,000 µg/1, and 28 µg/L respectively. URSGWC boring B-1 is located within the perimeter of the 2005 excavation (Figure 3) and the grab groundwater sample was collected from a total depth of 56.5 fbg. The total depth of the 2005 excavation was 8o fbg. There have been a total of four monitoring wells installed and subsequently monitored at the site (MW-1 through MW-4). Wells MW-1 through MW-3 were installed in August of 2000, and well MW-4 was installed in August 2001. The only analyte detected in groundwater samples collected