Fuel Oxygenates

In earlier newsletters, we have discussed the measurement of MTBE in groundwater in California. Although MTBE is the major fuel oxygenate, it is not the only compound used to meet Reformulated Gasoline (RFG) standards, and it is not the only oxygenate which has been found in California groundwater from fuel releases. The relative composition of oxygenates in gasoline is variable, and not indicative of any one refiner or distributor. Furthermore, these compounds may have uses other than as fuel blending agents.

Fuel oxygenates include: Methyl t-butyl ether (MTBE), Ethyl t-butyl ether (ETBE), t-Amyl methyl ether (TAME), Diisopropyl ether (DIPE), methanol, ethanol, and t-butyl alcohol (TBA). There is a lack of validated methods to measure these compounds in groundwater and other media.

One California laboratory, Global Geochemistry Corporation (GGC), has modified an ASTM method to measure the oxygenates in groundwater. In one case, GGC found MTBE and TAME in groundwater near a gas station. Fuel taken from the pumps at the presumed source did not have detectable TAME, so it was not useful in predicting what oxygenate may be in the groundwater. There is currently considerable discussion about the measurement of oxygenates in water and soil. Although ETBE and DIPE have not been found in California due to fuel releases, it is recognized that there is a potential for soil and groundwater contamination with all of these ethers and alcohols.

Methanol and ethanol are difficult to measure by the usual purge-and-trap methods, e.g., EPA 8240 and 8260, because of problems with purging from water, hydrocarbon interferences, and potential for lab contamination. However, methanol and ethanol are generally considered to be a lower priority for measurement due to their relatively low toxicity and relatively low persistence.

Validation studies

Lawrence Livermore National Laboratory has begun a validation study with the State Water Resources Control Board and other laboratories to validate methods for oxygenates, including modified ASTM D2887/D4815, EPA 8260, and EPA 8020 for the measurement of MTBE, TBA, DIPE, ETBE, and TAME in water, soil, and air. Preliminary work indicates that 8260 is viable for TAME, DIPE, and ETBE in groundwater, but additional validation is needed for water as well as air, soil gas, and fuel.

Monitoring

Routine monitoring requires verified test methods. Some regional water boards have begun adopting requirements for the measurement of the oxygenated ethers by EPA 8260; additional work needs to be done to develop cost-effective monitoring programs for the fuel oxygenates.

The development of methods for all commonly used oxygenates is a high priority so that monitoring for releases can be done reliably and cost-effectively.

Bart Simmons, Ph.D., is the Chief of the Hazardous Materials Laboratory, Department of Toxic Substances Control, Berkeley.