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1 <br /> ARCADIS Ms. Kathryn Dominic ' <br /> August 24, 2010 <br /> 1 <br /> (February 1996). PAHs were not detected in wells directly down gradient of the ' <br /> Biotreatment Beds or the TPCA ponds(e.g. MW-02A or MW-08A). <br /> RWQCB Request: The RWQCB requested in the February 19, 2009 letter to UPRR t <br /> that the groundwater downgradient of the Biotreatment Beds be sampled for PAHs. <br /> ARCADIS Response: ARCADIS did not analyze groundwater samples for PAHs ' <br /> because groundwater wells have been analyzed for PAHs in the past (1994, 1996 <br /> and 1997)and were detected below cleanup goals in wells directly downgradient ' <br /> (MW-02A and MW-08A)of the TPCA pond. Due to their insoluble nature, PAHs <br /> would not be expected to be present at elevated concentrations downgradient of the <br /> Biotreatment Beds. Soil samples in which PAHs were detected yielded little to no ' <br /> soluble PAHs in samples analyzed in both 1995 and 1996. Consequently, these data <br /> and the inherent properties of PAHs demonstrate that PAH concentrations have <br /> decreased in the excavated soils and do not pose a threat to groundwater. ' <br /> Furthermore, soil samples collected from the Biotreatment Beds in 1996 were below <br /> the soil cleanup goals as outlined in CAO No 92-720, indicating that bioremediation <br /> of PAHs in the Biotreatment Beds has occurred. t <br /> Metals in Soil and Groundwater ' <br /> Soil and groundwater samples have been collected from the TPCA pond and <br /> Biotreatment Beds and analyzed for various metals data. The soil data include the ' <br /> following: <br /> • In 1987, two soil borings(PD-1 and PD-3)were advanced in the TPCA pond, prior <br /> to excavation, to a total depth of 11 feet below ground surface(bgs)and 9.5 feet ' <br /> bgs, respectively. Eight soil samples were collected from PDA and five soil <br /> samples were collected from PD-2. Lead and chromium were detected at <br /> maximum concentrations of 19 mg/kg and 51 mg/kg, respectively.These results ' <br /> are consistent with samples taken from other locations on the Site that were not <br /> associated with the Biotreatment Beds. ' <br /> • In 1989, the RWQCB analyzed one sample collected from the stockpiled soil for <br /> lead.The lead concentration was 47 mg/kg(Industrial Compliance 1994A). <br /> • From 1990 to 1993, groundwater samples were collected from 35 A-and B-zone ' <br /> monitoring wells and analyzed for metals(including total chromium and lead). The <br /> maximum concentrations were: 280 mg/L for chromium at MW-3B in 1990; and ' <br /> 0.094 mg/L for lead at MW-9A in 1990. <br /> I <br /> Page: <br /> 6/12 I <br />