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August 10, 2001 <br /> San Joaquin County <br /> Public Health Services <br /> Environmental Health Division Fa <br /> Site Mitigation Unit <br /> 304 E Weber Street c <br /> Stockton, CA 95201 w <br /> Attention Dot Lofstrom <br /> Re Frank's One Stop co <br /> Dear Ms Lofstrom, <br /> Further to analyses of three NAPL samples and one gas pump sample by ZymaX <br /> forensics, Inc and reviewing historic monitoring well analyses and the site map you <br /> submitted, I have reached the following conclusions <br /> From first measured chemical analyses available, it appears that although TPI-Ig <br /> was high in wells MW-5 and MW-6, the concentration of benzene, toluene and MTBE <br /> was low (or ND) in these wells Xylenes were the hydrocarbons in highest <br /> concentration By contrast, the downgradient well MW-13 contained benzene <br /> concentration equal to or higher than xylene and increased with time until December 18, <br /> 2000, after which time the benzene concentration decreased abruptly from 1500 ppb to <br /> 8 8 ppb This well and the adjacent downgradient well MW-14 are the only ones with a <br /> high concentration of both MTBE and TBA and both contain measurable concentrations <br /> of TAME (an impurity in MTBE) Toluene concentration in MW-13 is much lower than in <br /> either MW-5 or MW-6, suggesting that during migration 1n a NW direction from the area <br /> of possible release (between MW-5 and MW-6), the groundwater was anaerobic <br /> (depleted to dissolved oxygen) which resulted in removal by bacterial metabolism of <br /> toluene and xylene but not impacting benzene or ethylbenzene to the same extent <br /> Analyses of the NAPL samples by ZymaX display relatively low toluene <br /> concentration relative to the reference newly dispensed pump gasoline, an enrichment <br /> of xylenes and an absence of benzene This is suggestive of a product that has been <br /> moderately water washed, retaining the least soluble and volatile hydrocarbons The <br /> C3-C10 analysis of the NAPL samples further illustrates that loss of volatiles has <br /> occurred, although biodegradation appears to have been minimal based on the <br /> relatively high olefin and paraffin contents These losses could also have occurred from <br /> site remediation, which by your report began in October 2000 <br /> Ms Dot Lofstrom -San Joaquin County -ZymaX 1D 24358 Page 1 of 1 <br /> Frank's One Stop <br /> www Zym aXfore nsics com 16921 Parthenia Street Ste 201-North Hills CA 91343+fax 818 893 8940 4o 818 893 4103 <br /> laboratory 71 Zaca Lane•San Luis Obispo CA 93401 +fax 805 544 8226+vox 805 544 4696 <br /> email torensccs@ZymaXusa cam <br />