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Work Plan—Bvron Road, Tracy,California June 16,2003 06-6102-00-2931-030 Page 4 collected from the Nicholaw property. Polynuclear aromatic hydrocarbons (PNA's) and TRPH were also detected in two soil samples from the Souza property. Groundwater samples collected and analyzed from the six wells did not contain detectable concentrations of petroleum hydrocarbons. Geomatrix performed groundwater-monitoring events at the Nicholaw property in April 1995, and June 1996. Groundwater was analyzed for TPHc, TPHd, TPHg, BTEX, and PAHs. Petroleum hydrocarbons were not present in groundwater above detection limits in any of the samples analyzed. Based on depth to groundwater measurements recorded by Geomatrix, groundwater beneath the site flowed toward the north-northwest at a gradient ranging from 0.003 to 0.01 ft/ft. Groundwater-monitoring wells associated with the Nicholaw property were abandoned on April 7, 1997. Subsequent to well abandonment, SJCEHD granted a"No Further Action"letter dated May 1, 1997. Monterosso Property Toxic Technology, Inc. (TTI) conducted a soil assessment of the Highiet/Monterosso property (Monterosso property) in October 1988. The soil assessment was performed following the installation of a water line by the City of Tracy, which encountered affected soil. Levine-Fricke (LF) reported that TTI advanced nine soil borings in the vicinity of the northern portion of the Monterosso property, approximately 125 feet south of Byron Road. Three additional soil borings were installed closer to the northern property boundary south of Byron Road. Petroleum hydrocarbons were not detected in any of the soil samples analyzed except for one sample collected from a depth of six feet bgs in a boring located 11 ft south of Byron Road. In January 1989, LF advanced 13 soil borings along the northern boundary of the Monterosso property. Ten of the soil borings were located south of Byron Road; the remaining three soil borings were located in areas suspected to have petroleum-affected soils. In addition to soil samples collected from the borings, samples were also collected at an approximate depth of five feet bgs from a trench excavated during the installation of a water line across the site. A total of 23 soil samples were collected and analyzed for TPH. In five samples from three of the soil borings, TPH was identified with a maximum concentration of 1,100 mg/kg at 10 feet bgs. Petroleum hydrocarbon detections varied with respect to depths and concentrations. In May 1990, LF installed four groundwater monitoring wells ranging in depth from 15 to 18.5 feet bgs. Soil samples were collected from each of the well borings, and analyzed for TPHd (Method 8015 modified) and BTEX constituents. Toluene was detected in all soil samples at concentrations ranging from 0.015 to 0.18 mg/kg. Groundwater samples collected were analyzed for TPH and BTEX. These analytes were not detected in the groundwater, with the exception of the sample collected from groundwater monitoring well MW-1, which contained detectable toluene at 0.3 micrograms per liter (jig/L)- Groundwater samples were collected from two of the four wells on April 5, 1996, from one well on April 25, 1996, and from a fourth well on May 3, 1996. At the request of Mr. Mike Infurna of San Joaquin County Public Health Services (SJCPHS), a second round of groundwater sampling and monitoring was performed on June 4, 1996. Samples were analyzed for total extractable hydrocarbons quantified as crude (TEH-C), total extractable hydrocarbons quantified as diesel (TEH-D), TPHg, BTEX, and PAHs. Petroleum hydrocarbons were not detected in any of the groundwater samples submitted for analyses. K:CVX-OVP\RO W—SITES\westsidechannel\draftworkplan.doc