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5•0 CONCLUSIONS <br /> The analytical results show a slight decrease Y g ease in hydrocarbon <br /> concentrations from last quarter There was a slight increase in <br /> tetrachloroethene (PCE) concentrations from last quarter, although the <br /> PCE concentrations are still very low <br /> The only well which showed a significant increase in hydrocarbons was in <br /> monitoring well MW-5 which contained free-floating hydrocarbons <br /> The 2-methylnaphthalate, bis(2-ethylhexyl)phthalate and di-n-butyl <br /> phthalate detected in groundwater samples collected from monitoring <br /> wells MW-6, MW-7, MW-8 and MW-10 are plasticissors, which are <br /> common sampling and laboratory contaminants since they are present in <br /> all plastic including pump tubing, laboratory tubing, gloves, etc The <br /> Ipresence of these compounds should not be considered a significant <br /> environmental concern at these concentrations <br /> fThe only hydrocarbon concentrations detected in groundwater samples <br /> which exceeded California Department of Health Services (DHS) <br /> maximum contaminant levels (MCLS) for drinking water were the toluene, <br /> ethylbenzene and total xylene concentrations in groundwater samples <br /> collected from monitoring well MW-6 and the benzene concentration in <br /> groundwater samples collected from monitoring well MW-7 It can b e <br /> assumed that the hydrocarbon concentration in monitoring well MW-5 <br /> would have exceeded DHS MCLs had the well been sampled None of t h e <br /> other- VOCs or SVOCs detected exceeded DHS MCLS for drinking water <br /> TPH-D was detected in several of the monitoring wells, including the on- <br /> site drinking water well However, the laboratory noted that none of the <br /> detected hydrocarbon concentrations in the diesel range had <br /> chromatogram patterns indicative of diesel-fuel contamination At the <br /> request of ASE, Chromalab reviewed the chromatograms and reported to <br /> ASE that the detected concentiations were definitely not related to diesel- <br /> fuel Chromalab stated that the patterns most resembled a lighter range <br /> hydrocarbon such as gasoline However, since the samples collected from <br /> MW-8, MW-9 and MW-10 did not contain detectable TPH-G, the TPH-D <br /> concentration may have been a result of carryover from the very high <br /> concentrations detected in the groundwater samples collected from <br /> monitoring well MW-6, which was analyzed prior to these samples <br /> Frank's One Stop Quarterly Report - August 199$ Sampling <br /> -4- <br />