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CHEVRON PIPELINE COMPANY <br /> Date: April 1987 through December 1995 <br /> Subject: Subsurface Investigation <br /> Prepared by: Western Geologic Resources, Inc. and Geomatrix Consultants, Inc. <br /> Addressee: Chevron Pipeline Company <br /> Summary: The site is located at the northwest corner of the intersection of the Grant Line and Corral Hollow <br /> Roads. In April 1987, an estimated 870 barrels of unleaded premium gasoline and diesel fuel were released into <br /> the surrounding soils due to the puncture. Approximately 840 barrels of product were subsequently recovered. <br /> On May 11, 1989, Western Geologic Resources (WGR) collected groundwater samples from 3 <br /> monitoring wells, 3 dewatering wells, and one non-operating domestic well. Peak concentrations <br /> (collected from the western edge of the release area) were reported at 1,200 ppb. Peak benzene <br /> concentrations were reported at 410 ppb. Oil and grease were also reported at 50 ppm. <br /> In early 1991, WGR drilled five soil borings and groundwater monitoring wells to evaluate the overall <br /> extent of impact to groundwater. Peak TPH and BTEX concentrations were reported at 1,300 ppm, 15 <br /> ppm, 73 ppm, 28 ppm and 140 ppm, respectively. Groundwater samples contained TPH, as gasoline, <br /> and BTEX concentrations of 120 ppm, 16 ppm, 18 ppm, 3.7 ppm, and 18 ppm, respectively. <br /> According to a letter from the California Regional Water Quality Control Board (CRWQCB) dated <br /> September 23, 1993, no further action has been conducted since 1991. <br /> In October 1995, the extent of impacted soil at the water table and the distribution of dissolved <br /> petroleum hydrocarbons in groundwater was determined. Soil impact is limited to the depth interval <br /> between approximately 8 and 12 feet below ground surface (bgs). Lateral extent of impacted <br /> groundwater is limited to an area approximately 160 feet long and 110 feet wide beneath the site. Peak <br /> TPH and BTEX concentrations in soil samples were reported at 1,500 mg/kg, 5,600 µg/kg, 75,000 <br /> µg/kg , 57,000 µg/kg , and 390,000 µg/kg, respectively. Results from the groundwater sampling <br /> reported peak concentrations at 20 mg/l, 4,500 µg/l, 190 µg/1, 1,300 µg/I and 3,400 µg/1. <br /> Recommendations for intrinsic bioremediation have been submitted to the CRWQCB, and actions are <br /> pending on state officials. <br /> IN 40007-088-01 <br /> uig�=w\97-06j un\arco frac.doc <br /> 5-3 <br />