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Chevron Environmental Management Company Soil and Groundwater Investigation Report Tracy Byron Road Project µg/L,respectively. When re-analyzed for TPHd following a silica gel cleanup, TPHd was not reported in these samples at or above the laboratory detection limit. Two grab groundwater samples were analyzed for TDS within this section. Concentrations of TDS in the water samples ranged from 1,800 mg/L (GW-20-15)to 2,100 mg/L(GW-24-15). Both grab groundwater samples exceed the recommended secondary MCL threshold of 500 mg/L. Groundwater affected by petroleum constituents does not appear to be defined through this section and the lateral extent is not known. Concentrations of residual petroleum in soil are presented on Figure 3c. Concentrations of petroleum constituents in groundwater are presented on Figure 4b. 6.4 SECTION SB-27 THROUGH SB-35-AREA BETWEEN CALDRON'S STORE AND AREA OF PG&E INVESTIGATION Borings SB-27 through SB-33, which correlate with dewatering wells#33 through#48, were located east of Caldron's General Store. Based on a review of the soil boring and dewatering well logs the presence of sheen or SPO was not observed. Soil samples analyzed from borings SB-27, SB-29, SB-31, and SB-32 did not contain concentrations of TPHc greater than 10 mg/kg. Three soil borings (SB-28, SB-30, and SB-33) contained concentrations of TPHc ranging from 7.2 mg/kg to 3,200 mg/kg. TPHc concentrations detected in samples collected from shallower depths in borings SB-28, SB-30, and SB-33 decreased significantly to 7.2 mg/kg or were not detected in the bottom of boring samples in this area. Lateral investigation of soil may be required for the shallow depths around borings SB-28, SB-30, and SB-33. Groundwater samples were collected from Hydropunch borings advanced adjacent to soil borings SB-29, SB-31, and SB-33. Concentrations of petroleum constituents were not detected in groundwater samples GW-29-18, GW-31-17, and GW-3 3-17 with the exception of fluorene at the concentration of 0.1 µg/L detected in sample GW-29-18. Four grab groundwater samples were analyzed for TDS within this section. Concentrations of TDS in the water samples ranged from 1,200 mg/L (GW-31-17)to 2,100 mg/L (GW-33-17). All grab groundwater samples exceed the recommended secondary MCL threshold of 500 mg/L. Borings SB-34 and SB-35 were advanced just north of the former Monterosso property in the southern easement of West Byron Road. The selected boring locations were in the vicinity of former borings B-10, B-14, and B-15 of the PG&E investigation. Analytical results of soil samples collected from borings SB-34 and SB-35 confirmed the presence of petroleum-affected soil. Trench excavation logs completed during the construction of the WSCO indicate intermittent pockets of petroleum-affected soil within this section of the TBRP investigation. TPHc concentrations of 2,300 mg/kg and 3,100 mg/kg were reported in soil samples collected from SB-34 at the depths of 6 and 12 feet bgs, and from SB-35 (4,500 mg/kg) at a depth of 7 feet bgs. Groundwater samples were collected from Hydropunch borings advanced adjacent to each boring. Concentrations of TPHd at 960 µg/L and 250 µg/L were detected in GW-34-19 and GW-35-18, respectively. Mr. Dean Hubbard of RWQCB was present during the installation of borings SB-34 and SB-35 and requested the collection of split grab groundwater samples from SB-34 and SB-35. Concentrations of TPHd exceeded the 100 µg/L Taste and Odor Thresholds in both samples following silica gel cleanup preparation. Concentrations of these constituents are consistent with those reported after the March 2003 PG&E investigation. Based on the laboratory analytical results,petroleum-affected soil and groundwater in the vicinity of SB-34 and SB-35 does not appear to be delineated and the lateral extent is unknown. Concentrations of residual petroleum in soil are presented on Figure 3d. Concentrations of petroleum constituents in groundwater are presented on Figure 4b. 10