MTBE in California's Public Drinking Water Wells: Have Past Predictions Come True?

Abstract

Extensive water quality monitoring data in California are now available for methyl tertiary butyl ether (MTBE) that span the past 16 years. The statewide database includes most of the active (and some inactive) public drinking water wells in the state, most of which have been repeatedly sampled for MTBE during 1995 to 2010. The cumulative detection frequency of MTBE in public drinking water wells in California at any concentration level is approximately 1.6% and 0.9% based on a one-detection criterion and two-detection criterion, respectively. The detection frequency of MTBE is approximately two to three times lower at concentrations above the state drinking water standards. Since 1996, the annual detection frequency of MTBE at any concentration level has ranged from 0.4 to 0.9% (one-detection criterion) and 0.2% to 0.7% (two-detection criterion). Despite repeated sampling, MTBE has been detected in only 1 or 2 years for most public drinking water wells that have ever been found to contain MTBE at any concentration level. The annual average detected concentration of MTBE has ranged from 5 to 16 µg/L (arithmetic mean) and 2 to 5.5 µg/L (median), excluding two outlier samples. MTBE detections are more prevalent in select geographic locations, rather than widespread across the entire state. The cumulative detection frequency for MTBE is approximately 1% for wells that belong to very small and small public drinking water systems (i.e., that serve between 25 and 3,300 people) and is approximately 2% for wells that belong to large and very large public drinking water systems (i.e., that serve >10,000 people). No detections of tertiary butyl alcohol (TBA) were found from 1996 to 2000, although few samples of TBA were collected during this time period. From 2001 to 2010, the cumulative detection frequency of TBA in public drinking water wells in California at any concentration level was approximately 1.4% and 0.2% based on a one-detection criterion and two-detection criterion, respectively. The cumulative detection frequency of tetrachloroethylene (PCE) in public drinking water wells in California is at least six times greater than that of MTBE and TBA, and unlike the trends observed for MTBE and TBA, PCE is often consistently detected in the same wells over time. The results of this analysis can be used to assess historical and current detections of MTBE in public drinking water wells in California. Also, if coupled with other chemical and site-specific information, the results can be used to assess potential future impacts of MTBE on drinking water supplies.Methyl tertiary butyl ether (MTBE) is an ether compound containing an oxygen atom bonded to two carbon atoms that is manufactured via the chemical reaction of methanol and isobutylene. Starting in the early to mid-1990s, this compound was widely used a fuel oxygenate in many regions of the United States in response to the 1990 Clean Air Act Amendments, which required an oxygenate be added to gasoline to reduce air emissions of ozone-forming volatile organic compound...

Life Cycle of Methyl tert-Butyl Ether in California Public Water Supply Wells

“…However, it is difficult to predict the time lag between decreases in contaminant concentrations observed at monitoring wells located close to the gasoline release location and the corresponding changes at public water supply wells located farther from the release locations. The frequency of MTBE detection in California public water supply wells was relatively stable between 2000 and 2010 . In other parts of the country, MTBE concentrations and detection frequencies in pubic water supply wells have begun to decrease in recent years .…”

“…The frequency of MTBE detection in California public water supply wells was relatively stable between 2000 and 2010. 8 In other parts of the country, MTBE concentrations and detection frequencies in pubic water supply wells have begun to decrease in recent years. 9 The goal of this study was to evaluate the prevalence of MTBE in groundwater recovered by public water supply wells in California and to evaluate the changes in detection frequency and concentration over time.…”