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to adequately define the extent of contamination. One boring should be completed to first groundwater. Additional borings may be required based on conditions encountered. Since no solvent contamination was encountered in the absence of TPH/BTXE during this sampling program, soil analysis by EPA m8015/502 will be adequate to determine contaminant extent. Several endpoint samples should be selected for EPA 8270 analysis to verify the absence of solvent contamination. If soil contamination is followed to within 10 feet of the present saturated zone one boring should be converted into a groundwater monitoring well. The boring in the presumed downgradient direction should be selected. In this event, a groundwater monitoring program will require development for submittal and approval by the Central valley Region, Water Quality Control Board. 5.3 Discharge Pit A more thorough site investigation is recommended for this study area. Specifically, three additional borings with associated soil sampling every 5 feet are recommended. Barings should be sited around the outside perimeter of the pit. One boring should be angled to terminate directly under the pit bottom. Based on conditions encountered, additional borings may be needed to fully define the complete extent of contamination. Since no solvent contamination was encountered in the absence of TPH/BTXE during this sampling program, soil analysis by EPA m8015/602 will be adequate to determine contaminant extent. Several endpoint samples should be selected for EPA 8270 analysis to verify the absence of solvent contamination. Presuming one deep boring is completed at the clarifier study area, the discharge pit borings need only be advanced under clear of the contaminated zone. If contaminated soil is followed to the saturated zone a groundwater well should be installed as described in Section 5 . 2 . 5. 4 Flightline Catch Basin The flightline catch basin is an enclosed concrete structure, consequently contaminants cannot escape from it into the immediate environment. No additional site investigation is proposed in the immediate catch basin vicinity. The storm drain system should be surveyed and additional downstream sediment samples collected to determine if contaminant concentra- tions are present. The possibility that other sources are con- tributing to downstream contamination should also be investigated. 20