MTBE in Groundwater: Status and Remediation

Abstract

The addition of methyl tertiary-butyl ether ~MTBE! to gasoline became controversial after its detection in waters of the United States. Probably the beginning of widespread public concern about MTBE came about after the detection of MTBE in the drinking water of the City of Santa Monica, Calif. Fifty percent of Santa Monica’s drinking water came from groundwater, which was found to be contaminated by underground storage tanks ~UST!. In August 1995, MTBE was detected in groundwater from one of two well fields, and by April 1996, the concentration was up to 610 mg/L. All of the wells from that well field ~the Charnock! were closed ~USEPA 2000!. Additionally, the United States Geological Survey ~USGS! National Water Quality Assessment Program ~NAWQA! found that MTBE was detected at a frequency of 16.9% in wells in urban areas and 3.4% in wells in rural areas ~Squillace et al. 1999! ~Fig. 1!. Of 60 volatile organic compounds ~VOC!, only trichloromethane ~chloroform! was detected with greater frequency. This result is rather remarkable, as MTBE has only recently been widely used as a gasoline additive. A more recent joint USGS/EPA study of 12 northeastern states that is examining MTBE and other VOC data in a random sampling of 20% of their drinking water supplies has so far detected MTBE in 7% of drinking water samples, with only 0.8% of the detected amount over 20 mg/L ~the lower boundary of EPA’s consumer advisory! ~USEPA 2000!. The joint USGS/EPA study also found that MTBE was detected more frequently in drinking water from areas with RFG or Oxyfuel than in areas without these fuel types and that there was very little cooccurrence of BTEX ~benzene, toluene, ethylbenzene, and xylenes! with the detection of MTBE. MTBE was initially added to gasoline to boost performance in the 1970s as alkyl lead additives were discontinued and was later added to improve air quality in accordance with the Clean Air Act ~CAA! Amendments of 1990. In 1992, oxygenated gasoline was required in areas that did not meet the carbon monoxide standard during the winter ~Wintertime Oxyfuel program!. In 1995, nine ozone nonattainment areas were required to use reformulated gasoline ~RFG! containing oxygenates year round. MTBE is added at concentrations from 11 to 15% by volume to oxyfuels and RFG ~Fig. 2!. It is the most commonly used oxygenate in RFG because it is low cost and produced from compounds avail-