Health and Environmental Assessment
Of the Use of Ethanol as a Fuel Oxygenate

• Peer reviewed citations for selected chapters

Concerns over the potential groundwater impacts of methyl tertiary butyl ether (MTBE) have prompted many states to ban or limit its use in reformulated gasoline. California took the lead in dealing with MTBE when Governor Gray Davis issued Executive Order D-5-99, which called for its removal from gasoline by no later than December 31, 2002. The primary alternatives to the use of MTBE in gasoline, which was used to meet mandated oxygen levels in reformulated gasoline, include the addition of ethanol or removal of the oxygen requirement altogether. In either case, the overall composition of gasoline will change in order to meet fuel vapor pressure requirements and to maintain the octane levels of the reformulated gasoline. One change that is expected to occur is the increased use of alkylates (i.e., branched alkanes) because of their high- octane content.

California requires that any new fuel introduced into the market place must undergo an evaluation of the possible environmental impacts that may occur. In December, 1999, a report entitled "The Health and Environmental Assessment of the Use of Ethanol as a Fuel Oxygenate" summarized the results of a screening analysis performed in fulfillment of the requirements of the Executive Order. As a result of this report, the California Environmental Policy Council found that the impacts associated with the use of ethanol will be significantly less and more manageable than those associated with the continued use of MtBE, but that further research was warranted.

The ongoing research conducted to meet the California Environmental Policy Council's requirements involved laboratory studies using field materials collected from a variety of fuel release sites, including a site where bulk ethanol was released. The results of this ongoing research was reported on October, 2001, in " Environmental Assessment of the Use of Ethanol as a Fuel Oxygenate: Subsurface Fate and Transport of Gasoline Containing Ethanol". These studies examined the:

• Behavior of ethanol-containing gasoline (gasohol) as it infiltrates through the unsaturated zone.
  
  
• Biodegradation kinetics of the gasoline components benzene, toluene, ethylbenzene, and xylenes (BTEX) in the presence of ethanol.
  
  
• Ethanol-related changes in subsurface bacterial populations (microbial ecology) that may influence the biodegradation rates of gasoline components.
• In addition to laboratory studies, further ground water impact modeling was performed and ethanol chemical analysis and sample handling methods were evaluated.

The proceedings of a workshop hosted by LLNL on the "Increased Use of Ethanol and Alkylates in Automotive Fuels in California" are also available.