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FARR ASSOCIATES <br /> TPH (TPH-g = 1.3 m /L}, diesel range TPH {TPH- <br /> d — 0.28 mg/L}, benzene (38µg/L), <br /> toluene (2.9 µg/L), ethylbenzene (58µg/L), and total xylenes (26 µg/L) (see also Figure 5). <br /> 1 This was the only sample from the August 1996 event that yielded detectable BTEX <br /> concentrations. TPH-d was detected in all of the wells sampled in August 1996, at concentra- <br /> �f - <br /> tions ranging from 0.13 mg/L in MW-4 to 2.5 mg/L in MW-1. TPH-g was only detected in = <br /> sample MW-2 where a concentration of 1.3 mg/L was yielded. No compounds were detected <br /> in the trip blank. <br /> As shown on Figure 6 and Table 2, benzene, ethylbenzene, and TPHg were reported at 2.6 <br /> ug/L, 2.4 ug/L, and 0.07 mg/L, respectively, for one of:the two groundwater samples <br /> F-41, <br /> collected from monitoring well MW-2 during the March 1997 event. The duplicate sample <br /> t <br /> from MW-2 was reported to have no detectable BTEX, TPHg, or TPHd. The sample from <br /> well MW-1 had 0.11 mg/L TPHd reported, and MW-3 had 0.07 mg/L TPHd reported (which <br /> f <br /> t is just above the 0.05 mg/L reporting limit). No compounds were detected in the trip blank. <br /> 5.0 CONCLUSIONS <br /> The soil-gas investigation detected petroleum vapors in the vicinity of the former Tank 3 <br /> location, indicating that some petroleumhydrocarbons remain in vadose-zone soils at the site. k <br /> However, the chemical concentrations reported for soil samples collected adjacent to the <br /> r highest detected soil-vapor concentrations indicate that'the.highest concentrations of petroleum <br /> hydrocarbons are relatively low (max. TPHk = 10 mg/kg; TPHg = 0.8 mg/kg, xylenes = 6 <br /> ug/kg). These concentrations of petroleum hydrocarbons in vadose-zone soiIs do not pose a <br /> significant risk to human health, safety, or beneficial uses of water. <br /> Although petroleum hydrocarbons continue to be detected in groundwater above Water Quality <br /> Objectives, the reported concentrations appear to be decreasing, and natural <br /> k <br /> attenuation/intrinsic bioremediation is expected to fully restore the site groundwater quality <br /> over a resonable period of time (e.g., 5 - 10 years). Thus, it appears that this site meets the <br /> criteria for a "low risk groundwater designation," as defined in the October 1996 draft revision <br /> i <br /> R4182OA-625960-9 <br /> } unionice/soilgaslwpd 9 <br />