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M. Scott Mansholt - 5 - 13 December 2006 Chevron/UPRR — TAOC Tracy C. el Pits ranged from 0.0049 to 3.71 mg/kg for the carcinogenic PAHs and exceeded the Cal-EPA CHHSL (0.038 mg/kg) at four locations — GMX-5, GMX-6, GMX-27 and GMX-32. The low concentrations of organochlorine pesticides DDD, DDE, DDT, and toxaphene detected in shallow soil were below the U.S. EPA Region 9 PRGs residential risk-based screening levels. Additionally, the dioxin toxic equivalency quotients (TEQs) results up to 0.34 pg/g were below Cal-EPA's residential screening value of 4.6 pg/g. Furans were not detected above the laboratory reporting limits in the four samples submitted for analysis. Low metals concentrations indicated that the metal results are within the range(s) expected for naturally occurring background values. VOCs were ND, except for naphthalene and 1,2,4-trimethylbenzene corresponding to two soil samples having elevated TPH concentrations. TPHd in groundwater was reported at 770 ug/I and 1,100 ug/I in two samples and the other three were ND. Groundwater was not collected from a sixth boring completed to 61-feet. PAHs were ND except for low concentrations of two PAHs in the boring GMX-27 in the water sample obtained beneath elevated TPH in soil reported at 11 .5-feet. VOCs were ND in the five groundwater samples. A well search of DWR records for the site vicinity did not identify supply wells downgradient, north of the site. However, an industrial well located on property adjacent to the west is 75- feet deep and screened at 40 to 60-feet. Since 770 ug/I TPHd was reported in GMX-24 at the northwest part of the site (depth to water approximately 40 to 50 feet), this well should be sampled to evaluate groundwater conditions lateral-downgradient of boring GMX-24. Conclusions Based on the 1989 to 2005 soil and groundwater investigations, it appears that soil in the gravel pit and the north-northeast part of the site has been impacted by TPH compounds. Vertical impact to soil appears to be defined by ND and/or low TPH concentrations to approximately 10 to 16.5-feet in several boring samples or exploratory trench locations. TPHd concentrations to 1,100 ug/I were reported in groundwater samples from borings located near the northern property boundary; but the offsite extent of impacts was not determined by the current or previous investigations. Additional delineation is needed to determine the extent of impacted groundwater downgradient, north of GMX-24 and north-northeast of GMX-26. For Regional Water Board staff to make a more thorough assessment of potential water quality impacts, water quality parameters for a representative number of site groundwater samples (in addition to TDS) should include General Minerals, electrical conductivity, ammonia as nitrogen, nitrate as nitrogen and total nitrogen.