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r� <br /> } ASS O C I ATE 5 I N C . <br /> MTBE was not detected in any other soil sample although some of the method detection limits <br /> were elevated due to dilution. <br /> In general, laboratory results suggest that residual soil contamination is present at the highest <br /> concentrations at approximately 10. ft. bgs and attenuates with depth to non-detectable levels at <br /> 30 ft, bgs. Petroleum constituents were again detected at 35.5 ft. and attenuated to non- <br /> detectable levels at 60 ft. bgs. Analytical results of soil samples are summarized in Table 1. <br /> ' 4.2 Groundwater Analytical Results <br /> The groundwater sample collected from boring SB7 contained concentrations of TPHg (4,700 <br /> 1 part per billion (ppb)), benzene (24 ppb), toluene (120 ppb), ethylbenzne (480 ppb), total xylenes <br /> (520 ppb), and MTBE (270 ppb). <br /> A review of the analytical data indicates that the benzene and MTBE concentrations detected in <br /> the groundwater sample exceed the current California water quality goals for drinking water. The <br /> established maximum contaminant level (MCL) for benzene is 1 ppb. The primary MCL <br /> established the California Department of Health Services (DHS) for MTBE is currently under <br /> development, however Cal/EPA's Office of Environmental Health Hazard Assessment (OHHA) <br /> has adopted a 13 ppb Public Health Goal for MTBE which is being utilized by DHS as an action <br /> level. Analytical results of groundwater samples are summarized in Table 2. <br /> ' 5.0 DISCUSSION <br /> Based on the analytical results and field observations, soil and groundwater beneath the location <br /> 1 of the former USTs are impacted by residual petroleum hydrocarbon constituents. The vertical <br /> extent of impacted soil and groundwater appears to be defined. However, the lateral extent of <br /> petroleum hydrocarbon constituents at or near the groundwater interface is undefined. In the <br /> 1 judgment of ATC, additional site investigation activities appear warranted to further evaluate the <br /> extent of impacted groundwater at the subject site. <br /> I� <br /> 1 <br /> �l <br /> w:192054.0001VeportslsumsbTdoe 5 <br />