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CONESTO3A-ROVERS & ASSOCIATES January 6, 2011 6 Reference No. 632277 • TPHg by EPA Method TO-3 • BTEX and MTBE by EPA Method TO-15 • Oxygen, Carbon Dioxide, and Helium by American Society for Testing and Materials (ASTM) Modified Method D-1946 The results of the current and previous sampling events are presented in Table 1. Copies of the soil vapor sample laboratory analytical reports and COC documentation are included as Attachment E. The current results are discussed below. The duplicate sample analytical results are not included in the following discussion, as similar concentrations within an acceptable range were detected in both samples. Please refer to Attachment E for the duplicate sample analytical results. Table 1 also presents a comparison with the San Francisco Bay Regional Water Quality Control Board (RWQCB) ESLs for shallow soil gas at commercial or industrial sites. The ESLs are for use as screening levels in determining if further evaluation is warranted, in prioritizing areas of concern, in establishing cleanup goals, and in estimation of potential health risks. As stated by the RWQCB, the ESLs are considered to be conservative. The presence of a chemical at a concentration above an ESL does not necessarily indicate that adverse impacts to human health or the environment are occurring; exceeding ESLs indicates that the potential for impacts may exist and that additional evaluation may be needed. Discussion of Results TPHg-was-detected in VP-1,ALP-2,andYR-3atconeentrations_nf100,0o0,o0Dilg/m3" 66,000 µg/m3, and 14,000 µg/m3, respectively. The concentrations in VP-1 and VP-2 exceeded the commercial/ industrial ESL of 29,000 µg/m3. • Benzene and ethylbenzene were only detected in VP-1 (26,000 µg/m3 and 6,600 ltg/m3, respectively) and VP-2 (6.3 µg/m3 and 10 µg/m3, respectively) . The concentrations in VP-1 exceeded the commercial/ industrial ESLs of 280 µg/m3 and 3,300 µg/m3, respectively. • Xylenes were only detected in VP-1 (3,200 µg/m3) . The detected concentration was well below the commercial/industrial ESL of 58,000 µg/m3. • No toluene or MTBE was detected. • Similar TPHg and benzene concentrations were detected in VP-1 relative to the October 2009 event, while the toluene and MTBE concentrations decreased (not detected) . Ethylbenzene and xylenes were not detected in VP-1 during the previous event, but the reporting limits were elevated. • In VP-2 and VP-3, higher TPHg concentrations were detected relative to the October 2009 event. No significant changes in concentration were reported for the other constituents. Worldwide Engineering, Environmental, Construction, and IT Services