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REVIEW OF PREVIOUS ENVIRONMENTAL AND GEOTECHNICAL STUDIES (cont.) <br /> 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 <br /> were released into the surrounding soils due to the puncture. Approximately 840 barrels of <br /> 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 <br /> overall extent of impact to groundwater. Peak TPH and BTEX concentrations were reported at <br /> 1,300 ppm, 15 ppm, 73 ppm,28 ppm and 140 ppm, respectively. Groundwater samples <br /> contained TPH,as gasoline,and BTEX concentrations of 120 ppm, 16 ppm, 18 ppm, 3.7 <br /> ppm,and 18 ppm, respectively. <br /> According to a letter from the California Regional Water Quality Control Board(CRWQCB) <br /> dated 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 <br /> interval between approximately 8 and 12 feet below ground surface(bgs). Lateral extent of <br /> impacted groundwater is limited to an area approximately 160 feet long and 110 feet wide <br /> beneath the site. Peak TPH and BTEX concentrations in soil samples were reported at 1,500 <br /> mg/kg, 5,600 µg/kg, 75,000 µg/kg, 57,000 µg/kg,and 390,000 µg/kg, respectively. Results <br /> from the groundwater sampling reported peak concentrations at 20 mg/1, 4,500 µg/1, 190 µg/1, <br /> 1,300 µ0 and 3,400 W 1. Recommendations for intrinsic bioremediation have been submitted to <br /> the CRWQCB, and actions are pending on state officials. <br /> D-3 <br />