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Work Plan—Byron Road. Tracy,California June 16,2003 06-6102-00-2931-030 Page 3 by EPA Method 8310. Benzene was not detected in the soil sample analyzed. However, TPHg, TPHk, TPHd, TPHc, and TRPH were detected at concentrations of 580, 260, 350, 860, and 820 mg/kg, respectively. The grab groundwater sample analyzed was noted as having separate phase oil entrained in the sample. Sample results were not considered representative of dissolved phase constituents in groundwater. On October 11, 1996, Geomatrix observed Precision Sampling advance one continuous core soil boring to an approximate depth of 15 feet bgs. Theboring was advanced to a depth below affected soil to assess groundwater quality beneath the site. One grab groundwater sample was collected from a screened interval between 10 and 15 feet bgs. The grab groundwater sample was submitted for analyses of TPHc with a silica gel preparation, BTEX, and PAHs. Petroleum hydrocarbons were not detected in the grab groundwater sample analyzed. San Joaquin County Environmental Health Department (SJCEHD) granted a "No Further Action" letter dated May 1, 1997. Nicholaw Property In 1990, a preliminary site reconnaissance and soil investigation were performed by Terrasearch, Inc. (Terrasearch), where eight soil samples from four random locations were collected at depths of one and three feet bgs using a 4-inch diameter hand auger. Soil samples were analyzed for TPHd and oil and grease (O&G). O&G was not detected in the soil samples analyzed. However, low concentrations of TPHd ranging between 3.3 and 4.8 mg/kg were detected in two of the eight soil samples analyzed. In 1994, Terrasearch performed an additional investigation at the subject property to further characterize soil and groundwater beneath the site. The scope of work included the installation of one groundwater monitoring well and advancement of nine soil borings completed to depths between three and 15 feet. Three soil samples and one groundwater sample were collected from the monitoring well, in addition to ten soil samples from the remaining soil borings. Water and soil samples were analyzed for Total Extractable Petroleum Hydrocarbons (TEPH) that includes TPHd, TPHc, and BTEX. Soil samples analyzed from six of the borings contained detectable concentrations of xylenes ranging from 5.6 to 9.3 micrograms per kilogram (pg/kg). The groundwater sample contained low concentrations of TPHd and BTEX compounds. According to the Terrasearch report, these contaminants were thought to have been derived from an outside source. Environmental Closures, Inc (ECI) conducted a soil and groundwater investigation that included the construction of three groundwater- monitoring wells. Soil and groundwater samples were collected and analyzed for TPH as gasoline, diesel, crude oil, kerosene, TRPH, O&G, BTEX, and PAH's. Petroleum hydrocarbons were detected in one of the three soil samples analyzed. Low concentrations of PA-Hs were detected in the soils collected from 5.5 feet bgs from two samples. Petroleum hydrocarbons were not detected in any of the groundwater samples analyzed. However, lead was detected at low concentration in one groundwater sample. In December 1994, Mill Creek Associates (MCA) conducted a soil and groundwater investigation of the Nicholaw property and adjacent Souza property. MCA installed a total of six groundwater-monitoring wells, three wells per property. Soil and groundwater samples were collected and submitted for analyses. Results of the MCA investigation confirmed moderate levels of petroleum hydrocarbons detected in soil K:CVX-O VP\ROW_SITES\westsidechannel\draftworkplan.doc