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INTERNATIONAL <br /> TECHNOLOGY <br /> CORPORATION <br />' February 18, 1993 <br /> IT Job No 190916 <br /> Mary Maeys <br /> San Joaquin County Health <br /> P O Box 2009 <br /> Stockton, CA 95201 <br /> re_QA/QC Anomalies <br /> Pacific Bell Facility UE042 <br /> 345 N San Joaquin Street <br /> Stockton, CA <br /> Dear Ms. Maeys: <br /> Recently you requested a review of QA/QC anomalies which occurred during the analysis of <br /> a soil sample collected from monitoring well MW-3, located at the above referenced site. <br /> The sample in question (#MW3-4) was collected at 20 feet below grade during installation of <br /> monitoring well MW-3 on December 8, 1991 The sample was analyzed for gasoline, diesel <br /> and BTEX using EPA methods modified 8015 and 8020. Upon analysis, 7.4 ppm gasoline, <br /> 0 006 ppm ethyl benzene and 0.013 ppm xylenes were detected. It was noted on the <br /> laboratory report that the compounds detected and calculated as low boiling hydrocarbons <br /> (gasoline) are due to a petroleum mixture other than gasoline Thus was noted since the <br /> chromatographic pattern did not match the gasoline standard pattern used for chromatographic <br /> interpretation <br /> The surrogate recovery percentages achieved during analysis of this sample were outside of <br /> acceptable criteria; therefore, although the recovery percentages do not warrant rejection of <br />' these results, the results achieved must be considered as estimates (qualitative, not <br /> quantitative) As the sample analyzed was a soil sample collected during well installation, it <br /> is a one-tune collection point and is not repeatable. Furthermore, no petroleum hydrocarbons <br />' have ever been encountered m groundwater samples collected from this well, which appears <br /> to indicate that the hydrocarbons originally detected in the soul may have been anomalies due <br /> to organic hydrocarbon impact, lab contamination or a highly limited area of impact which <br /> has naturally attenuated. The hydrocarbon levels encountered were so low that it does not <br /> appear that any further investigative actions are warranted in this area <br /> Regional Office <br /> 4585 Pacheco Boulevard .Martinez California 94553 • 510-372-9100 <br /> IT Coroc-crion is a wholly owned sujusidiary of International Technology Corporation <br />