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Lawrence Livermore National Laboratory To: James G. Giannopoulos State Water Resources Control Board From: Anne Happel, Ph.D. Lawrence Livermore National Laboratory, Lr530 Environmental Restoration Division 7000 East Ave., P.O. Box 808 Livermore, CA 94550 Date: August 6, 1996 STTB.IF.CT Comparison of EPA 8020 and EPA 8240 Analytical Results for Measurement of Methyl Ternary Buryl Ether (MTBE) in Ground Water Samples from LUPI'Sites. METHODS We have reviewed MTBE ground water data submitted to us by several oil companies, including Shell, Texaco, ARCO, and Unocal- We have evaluated data from ground water samples concurrently analyzed for MTBE using EPA methods 8020 and 8240. In order to compare the detection and quantification of MTBE by these two methods, we restricted our study to a total of 98 ground water samples that reported MTBE values greater or equal to 20 ug/L by EPA method 8020 and/or 8240. This data was evaluated for the occurrence of false positives and for the level of agreement between values reported by each of these analytical methods. The MTBE values detected by EPA methods 8020 and 8240 were compared without the assumption of =owledge of the true value by calculating the Relative Percent Difference (RPD). In this report, RPD values greater than 40% indicate an unacceptable level of disparity between the values obtained by these two analytical methods. RES 7LTS and DTSCUSSTON Occurrence of False Positives: There has been much discussion as to whether EPA method 8020 is adequate for determining MTBE concentrations in LUFI'ground water samples. Anecdotal information from analytical laboratories and remediation engineers report false positive detections of MTBE by FPA 8020. False positive cases Occur when RDA 8020 analysis, a gas chromatography/photo ionization detector(GCIPID) method,detects MTBE, while confirmation by EPA 87st0, a gas chromatography/mass spectrometry (GClMS) method, determines MTBE to be non-detect (ND). These mis-identifications of MBE by EPA 8020 analysis are attributed to the presence of other hydrocarbons (gasoline components) that may co- elute with_14TBE under standard GC/PID conditions used for BTEX analysis. In this data set, the overall occurrence of false positives by EPA 8020 was low. Among the total 98 MTBE positive samples only 2 false positives were reported (2% of samples with MTBE concentrations >20 ug(1.). As expected, false positives only occurred in samples that contained elevated concentrations of gasoline components (Table 1). False positives occurred in 44, of the samples (2 out of 50 samples) that contained BTEX and/or B compounds at concentrations greater or equal to 150 ug/L. No false negative samples occur.ed in this data set. .1nEqu1Gppan WS7w W-UrwwwglcJCSila •P.a5=gasl�,Gif*rA99.661-;xgonwffl(416)�trca-r„z9rosas'a9Viceutc XFt