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Attachment A:Previous Environmental Activities The investigation also evaluated the presence of TCE in Site soil at the request of the Central Valley Regional Water Quality Control Board (RWQCB). TPH quantified as crude oil (TPHc)was detected in soil at a concentration of 10,000 mg/kg at 37 feet bgs from GMX-3, and polynuclear aromatic hydrocarbons (PAHs)were detected at concentrations ranging from 0.007 to 0.55 mg/kg. TPHd, TPHg, PAHs,and BTEX were not detected in the groundwater sample collected from WFSMW-1. TPHg and TPHd were detected in the groundwater sample from GMX-6 at concentrations of 110 and 92 µg/L, respectively. Geomatrix concluded that TPHd in down-gradient groundwater samples was either at non-detect concentrations or below Central Valley RWQCB Water Quality Objectives (WQOs)9. TCE was not detected in the soil samples analyzed. The presence of TPHg, benzene, and naphthalene in GMX-6 was likely from the adjacent former Union Oil Service Station, and not from the former Old Valley Pipeline (OVP)or Tidewater Associated Oil Company (TAOC)pipelines. GEOMATRIX 2002 SOIL AND GROUNDWATER INVESTIGATION10 On May 20 and 21, 2002, Geomatrix advanced three soil borings (GMX-8, GMX-9, and GMX-1B)at the site to further assess the extent of affected soil and groundwater. TPHc were detected in soil from GMX-8 at concentrations of 8,000 mg/kg at 5 feet bgs and 1,200 mg/kg at 55 feet bgs, and at 5,100 mg/kg in GMX-1B at 30 feet bgs. Benzene was detected only in GMX-8 at a concentration of 0.067 mg/kg at 55 feet bgs. Toluene was detected in all samples at concentrations ranging from 0.006 to 0.58 mg/kg. Ethylbenzene concentrations ranged to 0.87 mg/kg in GMX-8 at 55 feet bgs. Xylenes were reported up to 2.1 mg/kg in GMX-1B at 30 feet bgs. Various PAHs were reported in the GMX-8 sample collected at 55 feet bgs, and in the GMX-1B sample collected at 30 feet bgs. GEOMATRIX 2003 OFF-SITE SOIL AND GROUNDWATER INVESTIGATION" The Central Valley RWQCB requested additional off-site assessment, and Geomatrix subsequently advanced three off-site soil borings (GMX-10, GMX-11, and GMX-12) between the former HPP-BTR pipelines and Welty Road. A TPHc concentration of 15,000 mg/kg was detected in the soil sample from GMX-12 collected at 41.5 feet bgs. Benzene, toluene, and total xylenes were also detected in soil from GMX-12. TPHd concentrations were detected in groundwater samples collected from GMX-10, GMX-11, and GMX-12 at 210, 3,600, and 110 gg/L, respectively. Geomatrix recommended that a search of California Department of Water Resources (DWR)files be conducted to identify water wells within 2,000 feet of the Site. 9. Central Valley RWQCB,2007. Water Quality Control Plan(Basin Plan)for the Sacramento River Basin and the San Joaquin River Basin,4th ed. October. 10.Geomatrix,2002. Report of Soil and Groundwater Investigation, US Can/Welty Road, Vernalis, California. August. 11.Geomatrix,2003. Report of Off-site Soil and Groundwater Investigation, US Can/Welty Road, Vernalis, California. November.