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7%D California Fuels '\ August 15, 1989 (89062) CONCLUSIONS AND RECOMMENDATIONS The available data suggest that an unauthorized release of fuel to the subsurface has occurred at the facility. Elevated levels of hydrocarbon vapors were detected around the tank fill ports and adjacent to the product delivery line. The highest levels of vapors (greater than 100 ppm) were encountered between the former cashier's office and the unleaded gasoline tank to the north. Due to dense, hard soils encountered at the facility, the depth of contamination could not be determined. The EHD indicated that they would require additional site assessment be conducted at the facility. The site assessment should include the drilling of borings to log, monitor, and sample the earth materials in the subsurface. The borings should be sampled progressively at depths of 5 feet by collecting undisturbed soil samples. The borings should be drilled and sampled until two consecutively uncontaminated soil samples, based on field criteria, are collected. The borings should be completed to ground water monitoring wells if contamination is encountered in the vicinity (within 10 feet) of ground water. If needed, three ground water monitoring wells should be installed to specifica- tions in Title 23 of the California Administrative Code (CAC) to determine the direction of ground water flow, the hydraulic gradient, and the potential impact of fuel contamination on ground water quality. In addition to the assessment, Staal, Gardner & Dunne, Inc. (SGD) recommends that overspill protection boxes be installed around the tank fill ports installed on each of the tanks and appurtenant piping. The overspill protection boxes should contain any product that may leak around the fill port during fueling operations of this facility. Because the tanks are more than 15 years old and are approaching the end of their service lives, the facility operator should consider replacement with new double-walled tanks (and double- walled piping) equipped with overfill protection and leak detection systems.