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' Ms Vicki McCartney Project No 88004OIA 0201 i. October 26, 2004 ' Page 7 tpathway is hydrocarbon volatilization from smear zone soils and groundwater to ambient air The potential exposure pathway for utility maintenance workers is tdermal contact with hydrocarbon-impacted soil and groundwater Based on these potential exposure pathways, and according to the San Francisco Bay RWQCB's Screening For Environmental Concerns At Sites With Contaminated Soil and Groundwater, dated July 2003 (updated ' September 4, 2003), no significant risk is present at the site The groundwater screening levels for the evaluation of potential indoor air impacts, assuming residential land use, which is more conservative than the current commercial use, are 24,000 µg/l for MtBE and 5,300 µg/1 for benzene The direct exposure screening levels for the construction/trench worker scenario are 2,800 parts per million (ppm) for MtBE and 17 ppm for benzene Based on the remaining petroleum hydrocarbon concentrations currently reported at the site, along with declining concentration trends in groundwater, there does not appear to be a significant threat to human health or the environment, or to any other potential beneficial uses of shallow groundwater beneath the site Appropriate conclusions and recommendations for the next phase of work The extent of impact to soil and groundwater appears delineated Additional assessment work is not warranted at this time In order to facilitate timely closure of the site, active remedial action appears appropriate ■ An updated Site Conceptual Model illustrating site conditions showing the extent ' of known soil and groundwater impact relative to the leaking UST system and the relationship between contaminants and potential receptors ' Figure 7 presents a site conceptual model of the site illustrating existing site conditions i Y'� ► r ' N 1sacDM20044Pr1188018800401A 4addoc Shaw Environmental,Inc