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Work Plan—Byron Road.Tracy,California June 16,2003 06-6102-00-2931-030 Page 7 concentration 5.1 pg/L) and petroleum hydrocarbons (maximum 27 mg/L TEPH). Based on the results of the screening HRA. Geomatrix concluded that exposure to contaminants of concern in either soil or groundwater does not result in unacceptable risks to future on-site residents. Geomatrix conducted two additional quarters of groundwater sampling of five wells within the area of affected soils. A new well was installed in May 1996 and also sampled in two events separated by one month. Geomatrix collected one soil sample from the well boring at first water and another at total depth of the borehole. The soil samples were analyzed for total purgeable petroleum hydrocarbons quantified as gasoline (TPPHg), TEPHd, and BTEX. Petroleum hydrocarbons were not detected in the soil samples analyzed. Groundwater samples from the newly installed well were collected in April and May 1996 and analyzed for TPPH, TEPH, and BTEX. Petroleum hydrocarbons were not detected in either sample. Geomatrix also conducted a well survey that identified an irrigation well located approximately 800-feet upgradient from the former pipeline location. Geomatrix concluded the well was unlikely to be affected by residual petroleum. In a letter dated October 11, 1996, the RWQCB issued a response to the Geomatrix Response to Request for Additional Information and Recommendation for Site Closure report, dated August 14, 1996, indicating no further investigation,remedial or removal action, or monitoring was required. Dobler Property In October 1998, a soil and groundwater investigation was conducted by Geomatrix to assess the possible presence of petroleum hydrocarbons on the property. Three soil borings were advanced to an approximate depth of 15 feet bgs. One sample from each boring was collected at either the zone of most visibly contaminated soils or just above the water table. Petroleum-affected soils were observed in one of the three borings from 8.5 to 9.5 feet bgs. Three soil samples were collected from the borings and submitted for analyses of TPHc, BTEX, and PNAs. Twoof the three soil samples did not contain petroleum hydrocarbons. However, TPHc was present at 2,100 mg/kg in one of the samples analyzed. Concentrations of pyrene (0.035 mg/kg) and chrysene (0.053 mg/kg) were also detected in this sample. Geomatrix also collected one grab groundwater from a boring, which was analyzed for TPHg, TPHd, BTEX, and PAHs. Petroleum hydrocarbons were not detected in the grab groundwater sample. The SJCEHD granted a"No Further Action"letter dated June 29, 1999. Surland Homes Property Geomatrix advanced eight soil borings in July 1998 to evaluate the lateral and vertical extent of petroleum-affected soils and to collect grab groundwater samples. Petroleum-hydrocarbon stained soils were observed in three of the eight soil borings advanced. Soil samples were collected from depth intervals where the soil appeared to be affected by petroleum, or directly above the water table. At a minimum, one soil sample was collected from each boring between 6 and 9.5 feet bgs. The samples were analyzed for BTEX,PAHs, and TPHc. Grab groundwater samples were collected from three borings and analyzed for TPHd,TPHg,BTEX,and PAHs. In three of the eight soil borings, TPHc was detected at concentrations up to 3,600 mg/kg. Benzene was not detected; ethylbenzene, toluene, and xylenes were either not detected or detected sporadically at low concentrations. Several PAHs were also present in three borings at low concentrations. In groundwater, K:CVX-OVP\ROW SITES\westsidechanneiW mftworkplan.doc