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Mr Harlin Knoll Environmental <br /> Resources <br /> Page 10 August 1998 Management <br /> Pa <br /> point of reference, all ground water results have been compared to Water <br />' Quality Goals (WQGs) established by the Central Valley Regional Water <br /> Quality Control Board (RWQCB) <br />' Concentrations of benzene detected in ground water from borings B-5 <br /> (2,300 ug/1) and B-6 (38 ug/1) exceeded the maximum contaminant level <br />' (MCL) for benzene of 1 ug/1 Toluene and xylenes were detected in <br /> ground water from boring B-5 at concentrations (310 and 6,500 ug/1, <br /> respectively) which exceed the MCLS for toluene (150 ug/1) and xylenes <br />' (1,750 ug/1) Concentrations of toluene, ethylbenzene, and xylenes from <br /> boring B-6 did not exceed the MCLS Concentrations of TBA were only <br /> detected in ground water from boring B-6 (86 ug/1) and did not exceed <br />' the MCL of 290,000 ug/1 Concentrations of TPH-g detected in the <br /> ground water from borings B-5 (46,000 ug/1) and B-6 (1,500 ug/1) <br />' exceeded the taste and odor threshold of 5 ug/1 for TPH-g It should be <br /> noted that these were grab ground water samples and may not be as <br /> representative as a sample collected from a monitoring well No floating <br /> product was observed in either of the boring B-5 or B-6 ground water <br /> samples <br />' CONCLUSIONS AND RECOMMENDATIONS <br />' Based on the results of this investigation, the TPH-g present in soil at the <br /> former tank location does not appear to be a continued source of benzene <br /> to ground water nor a threat to human health in its in situ state <br /> Although TPH-g is present in the soil, it is weathered, and the greatest <br /> areas of impact occur more than 10 feet above the water table with no <br /> appreciable amounts of benzene In addition, the depth of impacted soil <br /> relative to the ground surface is such that no human contact would be <br /> I expected given either the current or proposed use of the site Therefore, <br /> no further soil remediation is recommended at this site <br /> Ground water appears to be locally impacted with TPH-g, BTEX and <br /> TBA The ground water directly beneath the former tank location <br /> contains weathered gasoline and elevated BTEX concentrations Fifteen <br />' feet downgradient, however, the concentrations decrease substantially, <br /> suggesting the lack of a continued source to ground water and a limited <br /> zone of impact UPRR believes, therefore, that no further work is <br />