Evaluation of standard methods for the analysis of methyl tert-butyl etherand related oxygenates in gasoline contaminated groundwater

The U.S. Environmental Protection Agency (EPA) now requires monitoring of o xygenate compounds in groundwater at leaking underground storage tank (LUST ) sites nationwide. Three purge-and-trap gas chromatography methods most co mmonly employed for this purpose were tested, and their performance as a fu nction of total petroleum hydrocarbon (TPH) content of the sample matrix wa s determined. Tests included a formal method evaluation, a round-robin stud y, and a split-sample study (424 groundwater samples). Consistently good re sults were achieved with EPA Method 8240B/60B (mass spectrometry) and ASTM Method D4815 (flame ionization detection) when five oxygenates were monitor ed in reagent water and gasoline. However, one protocol routinely employed for analysis of LUST samples had serious limitations: EPA Method 8020A/21B (photoiozination detection) was unfit for monitoring of tert-butyl alcohol (TBA) and frequently yielded false-positive (12-50% of samples) and inaccur ate results when ether oxygenates were monitored in aqueous samples contain ing high concentrations of TPH ( 1000 mug/L). Thus, care should be taken in the analysis of LUST databases populated with EPA Method 8020/21 data beca use results reported for methyl tert-butyl ether (MTBE) in samples containi ng high levels of TPH have a high likelihood of being inaccurate or false-p ositive. For all three methods, detection limits determined in reagent wate r were sufficiently low for monitoring MTBE at the stringent primary (13 mu g/L) and secondary (5 mug/L) action levels set by the state of California.