SITE INFORMATION AND CORRESPONDENCE_FILE 1

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Wendy Cohen,SLIC Unit -3- I*.rr i February 1996 Y equivalent to the following concentrations in water: Unleaded Gasoline 1400 µg/1 Diesel Fuel 56 µg/1 JP-4 Jet Fuel 560 µg/1 JP-5 Jet Fuel 140 µg/1 These criteria are based on animal studies with whole fuel mixtures. They would be relevant to implementation of the narrative toxicity objective in the Basin Plan for these hydrocarbons in ground water. For BTEX, the most limiting criteria would be OEHHA's cancer potency factor for benzene (equivalent to 0.32 µg/1) and the following taste &odor thresholds: toluene 42 µg/1 ethylbenzene 29 µg/1 xylenes 17 µg/1 The only polynuclear aromatic hydrocarbon found during the four recent sampling periods was fluorene, with a USEPA reference dose (IRIS) equal to 280µg/1 in water. All samples in which fluorene was found had concentrations well below this health-based criterion. Data Quality and Quantity Issues Analytical quantitation limits have varied significantly during the investigation of this site. During the four recent sampling events (1994 and 1995) TPPH (gasoline-range hydrocarbons) quantitation limits were 500µg/l, ten times higher than the limit listed in the Tri-Regional Recommendations for Evaluation of Underground Tank Sites. TEPH (diesel-range hydrocarbons) quantitation limits were 20 times higher than listed in the Tri-Regional Recommendations. Quantitation limits equal to those listed in the Tri-Regional Recommendations were used during the 1992 sampling. Artificially high quantitation limits can magic the discovery of potential water quality impacts. The Regional Water Board monitoring program called for four quarters of ground water sampling; however,only three monitoring events have occurred under the program for wells MW 4A, MW-8A, MW-11A,MW-12A, and MW-13. In addition, a smaller set of analytes were run in the earliest sampling period for the other nine wells;TPPH and TRPH were omitted. Therefore, a full four quarters of ground water data have not been generated under the monitoring program. Field Study To examine the extent of biodegradative activity at the site, Geomatrix conducted a"Field Study" on samples from the wells with the greatest water quality impact (MW-13 and MW-23). To examine the potential contribution of entrained sediment, split samples from these wells were filtered prior to analysis for TRPH and diesel-range hydrocarbons (TEPH) and centrifuged prior to analysis for gasoline=range hydrocarbons (TPPH). To examine the contribution of"biogenic" hydrocarbons (formed by the degradation of petroleum hydrocarbons by microorganisms), silica . gel cleanup was performed on split samples from these wells prior to analysis for diesel-range hydrocarbons. To examine both effects together, split samples were cleaned up with silica gel prior to filtration and analysis for diesel-range hydrocarbons. I shared this information with our