ARCHIVED REPORTS_XR0002310 - Laserfiche WebLink

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Chevron Products Company Page 3 Former Chevron Station#9 8632,575 Grant Line Road,Tracy,California Jud 16,2001 • Benzene was detected in ten groundwater samples at concentrations ranging from 0 51 µg/L (CPT-11 at 18 feet bgs) to 31 µg/L (CPT-7 at 9 feet bgs) Toluene was detected in five groundwater samples at concentrations ranging from 0 58 gg/L (CPT-4 at 18 feet bgs) to 14 gg/L (CPT-10 at 18 feet bgs) Ethylbenzene was detected in thirteen groundwater samples at concentrations ranging from 0 66 ggCL (CPT-2 at 15 feet bgs) to 110 gg/L (CPT-6 at 23 feet bgs) Xylenes were detected in twelve groundwater samples at concentrations ranging from 0 68 gg/L(CPT-12 at 34 feet bgs) to 76 pg/L (CPT-14 at 16 feet bgs) MtBE was detected in seven groundwater samples at concentrations ranging from 4 8 µg/L (CPT-10 at 24 feet bgs) to 56 µg/L(CPT-9 at 16 feet bgs) EtBE,TBA, TAME, DIPE, EDB, 1,2-DCA, methanol, and ethanol were not detected above laboratory reporting limits in any of the groundwater samples collected DISCUSSION OF FINDINGS Based on the data collected during this assessment, there is little evidence that suggests petroleum constituent transport occurs from the site towards the offsite property near CPT-1 The highest detections of petroleum hydrocarbons were generally reported from the groundwater samples collected at CPT-6 through CPT-8, indicating groundwater generally flows towards those boring locations (northwest) This is consistent with the groundwater flow direction observed during all previous groundwater monitoring episodes performed at the site • Data also suggest that an area-wide diesel plume exists All of the soil and groundwater samples from the borings, including the samples from the offsite boring, contained low to moderate concentrations of diesel The highest diesel concentrations were detected at the downgradient borings on the site (CPT-6 through CPT-8), which suggests that the former Chevron station may have contributed to the diesel impacts in the area However, the detection of diesel in the offsite boring (upgradient of the site) indicates that the former Chevron service station, at the very least, is not the sole source of the diesel in groundwater j I Based on measured water-levels in the onsite wells, groundwater at the site was expected to be encountered at approximately 6 to 8 feet bgs, but was encountered at approximately 15 feet bgs This observation suggests the water-bearing zone may be semi-confined The majority of the sediments encountered were fine grained with the exception of a sand lens in the area around CPT-10 The highest concentrations of hydrocarbons in groundwater generally occur in the area of CPT-6 through CPT-8 Vertical definition to non-detect levels was not achieved in the deeper groundwater samples collected from CPT-10 (24 feet bgs) and CPT-12 (34 feet bgs), however concentrations of hydrocarbons generally decreased significantly with depth i 11Chevron1986321Reports12001 CPT seteassess doc