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Work Plan—Byron Road. Tracy,California June 16,2003 06-6102-00-2931-030 Page 6 A Phase II site assessment of the south parcel was conducted in August 1991 by TTI. Eleven soil borings were advanced and sampled, 10 groundwater-monitoring wells were constructed, and two groundwater- monitoring wells were abandoned. Petroleum hydrocarbons were present at 5 to 15 ft bgs in five of the locations. One well had detectable concentrations of petroleum hydrocarbons in the groundwater. In April 1992, TTI excavated 10 trenches to depths ranging from 7 to 15 feet bgs. Petroleum hydrocarbons were observed as free product in soil and groundwater in five of the trenches near the southem property boundary. The RWQCB was notified of TTI's observations. In June 1992, TTI conducted an additional investigation of the southern parcel that included: trenching of 34 locations to depths ranging from 10 to 20 feet bgs. Free product was observed in four of the trenches located along the southern parcel boundary. In July 1992, TTI excavated five exploratory trenches west of the Dividend property. Soil samples were collected at each change of color ranging in depth from 9.5 to 12 feet bgs. One grab groundwater sample was also collected. Soil and the grab groundwater samples were analyzed for BTEX and TPHd. In addition, soils were analyzed for. TRPH. TPHd was identified in every soil sample at concentrations ranging from 110 to 320 mg/kg. Concentrations of TRPH, ethyl benzene and xylenes were also present in the soil samples analyzed. In the grab groundwater sample, TPHd, ethylbenzene, and xylenes were detected at 68,7,and 183 µg/L,respectively. In August 1992, Erler & Kalinowski, Inc. (EKI) performed a field investigation in order to identify petroleum hydrocarbons occurring in soils, assess groundwater impacts, identify sources, and define groundwater flow direction. Fieldwork included installation of five monitoring wells and eight soil borings. Petroleum hydrocarbons were observed in all but three of the borings at approximate depths from 5 to 16 feet bgs. Select soil samples were analyzed for TPH, PAHs, and fingerprint analyses. In all soil samples analyzed, TPH was detected at concentrations ranging from 1,841 to 23,907 mg/kg. Groundwater samples from the five newly installed wells and ten of the existing site wells were collected by EKI. Analysis included total purgeable petroleum hydrocarbons (TPPH), TEPH, BTEX, and total dissolved solids(TDS). Detection of BTEX compounds was at low levels with a maximum concentration of 12 pg/L of toluene. Concentrations of TPPH were detected in groundwater samples collected from three wells only. Extractable hydrocarbons characterized as diesel were encountered in 6 of the 15 wells sampled. Concentrations of TDS in the five newly installed wells ranged between 1,700 and 2,500 mg/L. In 1995, Geomatrix conducted additional soil assessments and groundwater monitoring on behalf of ChevronTexaco in support of a revised screening health risk assessment(HRA). Twenty-two soil borings were advanced in February 1995 to a maximum depth of 7 feet bgs. One sample was collected from this depth in each boring. Samples were analyzed for BTEX, TEPHc, and PAHs. Four soil samples received additional PAH analysis by an alternate method. Concentrations of BTEX were not detected in any of the soil samples analyzed. Total extractable petroleum hydrocarbons as crude was detected in soil samples from 11 of the soil borings, at concentrations ranging from 310 to 7,500 mg/kg. Five PAHs were present at low concentrations. As part of the revised screening HRA, Geomatrix conducted quarterly monitoring and sampling at the Dividend Property from August 1994 through August 1995. Samples were analyzed for TRPH, TPPH, TEPH, PAHs, and BTEX. Several wells exhibited minor concentrations of fluorene (maximum K:CVX-OVP\ROW_SITES\westsidechannel\draftworkplan.doc