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M. Scott Mansholt - 4 - 13 December 2005 Chevron/UPRR — TAOC Trac ravel Pits Toxicity equivalence factors (TEFs) derived by the World Health Organization and endorsed by OEHHA, are used to estimate toxic equivalency quotients (TEQs) for dioxin. The TEQ values are 0.18 pg/g for GMX-27-11.5, 0.00099 pg/g for GMX-32-1 .0, and 0.00053 pg/g for GMX-34-5.0, for dry weight results. The wet weights were slightly lower. The TEQ dioxin concentrations in the sample from GMX-27-11.5 (0.18 pg/g) are similar to the TEQ results (0.27 and 0.34 pg/g) found in two samples of similar material analyzed during the 2003 investigation. The TEQs reported for dioxin are below the Cal-EPA OEHHA residential screening value of 4.6 pg/g. Groundwater Groundwater samples were obtained from five borings (August 2005) at approximate depths of 55 to 60-feet using temporary grab-groundwater sampling devices. Two of the five samples reported TPHd concentrations of 770 ug/I (GMX-24) and 1,100 ug/I (GMX-26). Samples from GMX-25, 27, and 28 were ND for TPHd. No VOCs or TPHg and most of the PAHs were ND; low concentrations of two PAHs at or slightly above reporting limits were present in GMX-27, which reported more than 100,000 mg/kg TPH in the 11.5-foot soil sample. Groundwater was not encountered in a sixth boring, GMX-29 that was completed to a total depth of 61-feet. Geomatrix conducted a well search of Department of Water Resources (DWR) records identifying seven wells - north, east, and west of the site. None of the wells identified were immediately downgradient of the anticipated groundwater gradient to the north. At least 16 monitoring wells (of unknown depth or construction design), for monitoring chloroform in groundwater, were reported on the adjacent Georgia-Pacific property west of the gravel pits. Additionally, one industrial well, approximately 400-feet to the northwest, located on the Georgia-Pacific property adjacent to the west, is 75-feet deep and screened at 40 to 60-feet. This well should be selected for sampling since boring GMX-24 (TPHd at 770 ug/1) is located nearby in the northwest corner of the gravel pits site. Summary Soil samples and observations from borings and excavations completed at the site suggest that petroleum hydrocarbon compounds have not significantly affected soil within the southwest one-third portion of the site, south-southwest of the gravel pits. Elevated TPH concentrations in soil were found primarily on the north-northeast portion of the site and generally in the upper 10 to 12 feet. Soil samples obtained from beneath affected soil at 11 .5-feet in SB-27 was over 100,000 TPH. The 16.5-foot sample from this same boring reported TPHd at 3.3 mg/kg. Other borings similarly reported ND or very low TPH concentrations in the 10 to 16.5-foot samples from beneath affected soil. Thus, based on the borings completed to date, it appears the vertical extent in soil is limited to approximately 10 to 12-feet in the north-northeast portion of the site. PAHs were detected in 20 soil samples from both investigations with the elevated values corresponding to the soil samples having elevated TPH concentrations. Benzo(a)pyrene (B(a)P) was present at concentrations ranging from 0.0065 to 1.7 mg/kg. The B(a)P TEFs