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rISL OEOMYTRIX • Petroleum hydrocarbon affected soil has been encountered at the site at depths ranging between 7 and 19 feet bgs. The lateral extent of affected soil on the western portion of the property has been delineated. The lateral extent of affected soil on the eastern portion of the property has been delineated to the east,west,and south(Figure 2). Additional investigation is necessary to delineate the extent north of boring GMX-32. • Groundwater quality downgradient of the western area of affected soil is characterized by a grab groundwater sample from boring GMX-25. TPHg,BTEX,and PAHs were not detected in this sample. Material quantified as TPHd(without a silica gel preparation procedure)was detected at 86µg/1,which is below the diesel taste and odor criteria that is used as a water quality objective(WQO)by the Regional Water Quality Control Board—Central Valley Region(RWQCB). It should be noted that TPHd was not detected following a silica gel preparation procedure,indicating that constituents quantified as'TPHd"(without silica gel)is soluble polar biogenic byproducts resulting for intrinsic bioremediation of residual petroleum hydrocarbons in soil. • Groundwater downgradient of the eastern area of affected soil is characterized by grab groundwater samples from borings GMX-30,GMX-31 and GMX-33;however, groundwater downgradient of boring GMX-32,where petroleum hydrocarbon affected soil was encountered,has not been characterized. TPHg,benzene,ethylbenzene and PAHs were not detected in any ofthese samples. Toluene and xylenes were detected at concentrations well below their respective WQOs(e.g.,the drinldng water maximum contaminant levels are 150 and 1750µg/l,respectively). Constituents quantified as TPHd(without a silica gel preparation procedure)were detected at concentrations of 140 to 560µg/1,which is above the diesel taste and odor criteria that is used as a WQO by RWQCB. It should be noted that TPHd was not detected in any of the samples following a silica gel preparation procedure,indicating that the material quantified as"MHd" (without silica gel)is soluble polar biogenic byproducts resulting for intrinsic bioremediation ofresidual petroleum hydrocarbons in soil. • Groundwater within the area of affected soil is characterized by grab groundwater samples from borings GMX-6 and GMX-29. MTBE was not detected Benzene, toluene,ethylbenzene and xylenes were detected at concentrations below their respective WQOs(e.g.,the drinking water maxim=contaminant levels are 1, 150,700 and 1750 µg/1,respectively). Very low concentrations gess than 1 µg/1)of two PAHs(fluorene and phemmthrene)were detected. TPHg was detected at 140µg/1 and constituents quantified as TPHd(without a silica gel preparation procedure)were detected at a concentration of 660µg/I,which is above the diesel taste and odor criteria that is used as a WQO by RWQCB(100µg/1). Results from sample aliquots that were filtered prior to extraction and analysis(360µg/1)and treated with a silica gel preparation procedure(160 µg/f)indicate that much of the original'TPH&'quantification is due to non-dissolved constituents adhered to particulates in the sample and soluble polar biogenic byproducts resulting from intrinsic bioremediation of residual petroleum hydrocarbons in soil. • A human health screening evaluation was previously performed by Geomatnx (Geomatnx,2000)based on the methodology presented in the PEA. This evaluation \%1`3\OEP ATAXnOC SA�S1W 7W370M9O SOILGW R OVM .DOC 7