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Field Sampling Plan for the Former UST Location at Stockton FMS #24 California Army National Guard Table 3-1. (Continued) Notes: Bold indicates contaminant concentration exceeds 100 mg/kg (the recommended Tri—Regional Board guideline for TPHG or TPHD in soil). Lead concentrations were compared to the California Modified PRG of 150 mg/kg. Benzene concentrations were compared to the California Modified PRG of 0.64 mg/kg. Ethylbenzene and Toluene concentrations were compared to the PRG number for sat (soil saturation). Xylene concentrations were compared to the PRG number for nc (noncancer). Contaminant concentrations reported less than reporting limits are considered non—detect (ND). Sources: Versar, Inc., 2004 EPA, 2004 Regional Water Quality Control Board, 1990 3.2.2 Soil samples were collected from three boring locations around the vicinity of the previous USTs as follows: B30 located northeast of the UST excavation; B31 located southeast of the UST excavation; and B32 located northwest of the UST excavation (see Figure 3-1). Soil samples were analyzed for the following; TPHG, TPHD, BTEX and oxygenates, and lead by United States Environmental Protection Agency (EPA) Methods SW8015G and D, SW8260B, and SW6010B, respectively. Results of the soil sampling analysis indicate that the maximum concentration of TPHD was 260 mg/kg at a depth of 35 feet bgs in boring B31, which is greater than 100 mg/kg (the recommended Tri -Regional Board guideline). The highest concentrations of ethylbenzene (up to 18 mg/kg) and xylenes (up to 50.4 mg/kg) were also reported at the same depth and boring. The maximum detected concentration of ethylbenzene (18 mg/kg) is less than its residential Preliminary Remedial Goal (PRG). All detected concentrations of xylenes in soil were less than residential PRGs. The detected concentrations stated above indicate that soils beneath the area southeast of the previous diesel UST location have likely been impacted by leaks from the former diesel UST and contaminant concentrations are present within soil greater than Tri -Regional Board Guidelines but less than residential PRGs. The maximum concentration of TPHG present in soils at the location of the former USTs was in boring B30 at a concentration of 47 mg/kg at a depth of 40 feet bgs, which is less than 100 mg/kg (the recommended Tri -Regional Board guidelines). The highest concentrations of benzene (up to 1.2 mg/kg) and toluene (up to 0.88 mg/kg) were also reported at the same depth and boring. All detected concentrations of benzene and toluene in soil were less than residential PRGs. The concentrations stated above indicate that soils beneath the area northeast of the previous gasoline UST location may have been impacted by leaks from the former gasoline UST and contaminant concentrations are present within soil less than Tri -Regional Board Guidelines and residential PRGs. Fuel oxygenates were not detected in any of the soil samples collected at borings B30 through B32 at the former UST location. Lead concentrations were detected in boring B31 and B32. The maximum concentration of lead detected was 10 mg/kg at a depth of 40 feet bgs in boring B32, which is less than its residential PRGs. Figures 3-2 through 3-4 show the detected concentrations for each analyte at 25, 35, and 40 feet bgs, respectively. At 25 feet bgs, no analyte concentrations had been detected except for lead. The detected lead concentrations were less then its residential PRG. At 35 feet bgs, TPHD, TPHG, BTEX, and lead concentrations were detected less then 100 mg/kg and residential PRGs; however, of those concentrations only one analyte (TPHD [detected at 260 mg/kg]) had concentration levels detected greater than 100 mg/kg. Concentrations of TPHD have not been defined laterally from boring B31 at 35 feet bgs in all directions except to the x:Nwprocess\tw251 \CA ARNG\Stockton FSPTINAUStockton FSP.doc 10 August 2006 1