Abstract

The properties of methyl tertiary-butyl ether (MTBE) that are pertinent to subsurface fate and transport and their significance is discussed in the context of contaminant transport and remedial techniques. Due to its high water solubility relative to gasoline hydrocarbons, MTBE is more likely to be leached into groundwater or infiltration. Gasoline that is 11% MTBE (the nominal standard for air pollution uses) is determined to have the potential of creating groundwater concentrations of up to 3,990,000 (μg/L and gas-phase concentrations of 85,000 mg/m³. Due to its high volatility when dissolved in gasoline, vapor extraction is an appropriate approach for remediation of vadose-zone MTBE contamination from gasoline releases. Comparison of vapor extraction remediation of vadose-zone MTBE contamination due to gasoline releases to remediation of benzene from gasoline releases or of neat PCE shows MTBE to be similar to those two contaminants for which the technique is often used. However, the high water solubility of MTBE makes stripping less effective as a remedial technique for dissolved concentrations. Statistics for Los Angeles and Ventura counties near Los Angeles, California, show that 82% of stations have concentrations above the California health advisory level of 35 μg/L in groundwater and that the thickness of the vadose zone has no effect on groundwater MTBE contamination. At one location in Southern California, MTBE was seen to represent the leading edge of the contaminant plume from a gasoline release, and MTBE effects on cross-gradient wells indicate that MTBE can migrate in the gas phase to affect groundwater that is not downgradient of the spill.