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Parsons Engineering Science, Inc mg/kg), SB$-25 (960 mg/kg) and SBS-30 (160 mg/kg)] contained TPH-D at levels in excess of 100 mg/kg Re ulator Evaluation of Site Groundwater Contamination g Y Both PHS-EHD and the RWQCB staff generally utilize drinking water standards as guidelines for assessment of groundwater remediation standards Numerical drinking water quality standards (primarily Maximum Contaminant Levels (MCLS)] are published for the BTEX compounds detected and are listed in Table 3 However, no MCLs have been published for TPH-D The only contaminant detected at a concentration in excess of its MCL was benzene However, benzene was only detected in one sample (MW-3, June 1993) and the reported concentration (0 7 ug/L) only slightly exceeded the MCL (0 5 ug/L) No other BTEX compound has ever been detected in excess of its MCL either before or after June 1993 Although relatively high levels of TPH-D have been left in place in subsurface soils with w the potential to adversely impact groundwater in the vicinity of the former UFST, they do not appear to have done so For 10 of the 17 groundwater sampling events, TPH-D was not detected in all wells sampled This includes the most recent event (September 1996) With the exception of the concentrations of TPH-D detected in MW-3 and MW-2 in June 1996 (which are probably anomalous), concentrations of TPH-D, when detected, have been in the vicinity of or below 100 pa/1 It is likely that remaining residual soil contamination is isolated in small pockets and will either attenuate before reaching groundwater or as soon as it encounters groundwater Thus, based on historical data, TPH-D in soil does not appear to impact groundwater quality beneath or downgradient of the site Due to the fact that gasoline was never used at the terminal and TPH-G was not detected in the soil and groundwater samples analyzed for TPH-G, it is not a contaminant of concern Since TPH-G is not a contaminant of concern at the site, the additives to gasoline (i e methyl tertiary butyl ether, 1,2-dtchloroethane, tetraethyl lead) should also be of no concern at the site Groundwater seepage probably occurs along Mormon Slough, located approximately 1,300 feet downgradient of the Greyhound site Therefore, analytical results from groundwater at the Greyhound site should be interpreted based on potential impacts of contaminated groundwater on WQOs for surface water at Mormon Slough These WQOs include the WRCB's policy of non-degradation of existing water quality or the beneficial uses of that water body In view of the lack of beneficial uses of groundwater at the site and distance of the UFST release to Mormon Slough, there is a low potential for impending risk to human health and the environment resulting from groundwater contaminated by the former UFST Both soil and groundwater samples recently collected from downgradient well MW-4 support this conclusion PARESSYROI VOLIR 1WP1727607 80969127607803 WW6 11