ARCHIVED REPORTS FINAL SITE INVESTIGATION

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FMS #24 Site Investigation Report California Army National Guard • Toluene was detected at 98,000 ppbv. • Ethylbenzene was detected at 16,000 ppbv. • Total xylenes (m,p-xylenes and o -xylene) were detected at 30,200 ppbv. 3.3.4 Groundwater samples were collected in each boring at the first encountered water (see Tables 3-5A, 3-5B, and 3-6 and Figure 3-9). As with the soil results, primary contaminants detected were BTEX and TPH compounds, with the maximum concentrations detected as follows: • Benzene was detected at 73,000 µg/L in boring FMS24SB05 (MCL is 1 µg/L). • Ethylbenzene was detected at 7,100 µg/L in boring FMS24SB04 (MCL is 300 µg/L). • Toluene was detected at 45,000 µg/L in boring FMS24SBOI (MCL is 150 Rg/L). • Total xylenes were detected at 39,000 µg/L in boring FMS24SB04 (MCL is 1,700 µg/L). • TPHD was detected at 7,700 µg/L in boring FMS24SBOl (EPA taste and odor threshold is 100 4g/L). • TPHG was detected at 450,000 µg/L in boring FMS24SBOI (EPA taste and odor threshold is 5 4g/L)• 3.3.5 In summary, the May 2007 URS investigation showed that soil, soil gas, and groundwater contamination extends in all directions from the former USTs, and that BTEX and TPH concentra- tions exceeded regulatory clean-up levels. hi addition, the lateral and vertical extent of contamination was not defined. Based on these results, a second phase of sampling was conducted by URS in October 2007. 3.4 URS October 2007 Site Investigation 3.4.1 The site investigation conducted by URS in October 2007 included the collection of soil and groundwater samples from six HSA borings (FMS24SB06 through FMS24SB11) and four soil gas samples from shallow direct -push probes (FMS24DP01 through FMS24DP04) for analysis by an on- site laboratory. The borings were placed further from the former UST initial five borings to help define the lateral extent of contamination. Soil, soil gas, and groundwater samples were analyzed by the on-site lab for BTEX and TPHD/TPHG compounds. Direct -push shallow soil gas samples were collected at 8 feet bgs adjacent to four buildings in the vicinity of the USTs, to determine whether a potential health risk exists to workers within the buildings. 3.4.2 All soil samples collected for analysis (at 30 and 40 feet bgs in each boring) showed non - detect for all analytes. Following the completion of the first four step -out borings (SB06 through SB09, located approximately 300 feet to the north, east, south, and west of the Phase 1 borings), two additional borings (SB 10 and SBI l) were completed based on concentrations detected in ground- water samples in borings SB06 and S1307. In summary, the groundwater samples collected from SB06 and SB07 were the only samples containing BTEX and TPHD/TPHG compounds; all other groundwater samples showed non -detect for all analytes. The groundwater sample from soil boring SB07 (north of the former USTs) contained only low concentrations of BTEX compounds (all below MCLs) and 5,000 µg/L of TPHD (EPA taste and odor threshold is 100 pg/L); samples from the 6 December 2007