Gasoline and its additives have historically been a hot topic in the environmental arena, and they have recently made headlines again with the proposed increase of ethanol use in our gasoline. Throughout the years, changes to gasoline additives have improved our vehicle mileage, reduced emissions to the air, and have at least tried to align with the U.S. Environmental Protection Agency’s (EPA’s) mission to protect human health and the environment. But they have also left behind some interesting fingerprints, especially at soil and groundwater cleanup sites.

Gasoline additives have been in use since the 1920s. Lead was added to gasoline as far back as the 1920s, as an alternative fuel to reduce “knocking,” boost octane, and prevent the buildup of deposits within the engine. Lead was phased out in the 1980s, due to identified adverse health risks. In 1990, Amendments to the Clean Air Act required the use of oxygenated gasoline in areas with unhealthy levels of air pollution. As a result, between 1992 and 2005, Methyl tert-butyl ether (MTBE) became the oxygenating additive of choice,but it was later found to have detrimental effects to groundwater from emissions and/or spills, due to its high solubility and resistance to biodegradation. As a result, MTBE was phased out and replaced with Ethanol, which is a corn-based additive that provides the beneficial oxygenation required by the Clean Air Act, while also meeting federal requirements for renewable fuels.

Since the 1970s, when oil became more expensive and subject to international disputes – and as worries rose about the environmental damage caused by fossil fuels – the U.S. government has used various policy incentives to encourage the use of ethanol and other environmentally friendly supplements to gasoline. As a result, ethanol reportedly makes up about 10 percent of current U.S. gasoline usage.

For several years, Federal regulations have allowed the sale of ethanol-containing fuels with up to 15 percent ethanol (known as “E15”). However, most U.S. service stations only provide “E10,” because the more corrosive E15 can cause damage to older model cars. There has been much debate over the pros and cons of E10 versus E15, as many say that E10 provides sufficient oxygenation to make gasoline burn more cleanly and reduce air pollution. And, while it might be assumed that E15 would be better for air quality, the EPA currently blocks the sale of E15 from June 1 to September 15 in areas where smog is a problem, due to the volatility of the fuel, and the greater evaporation of gas during those warmer periods possibly causing more smog. Still, with the overall push for alternative fuels, the changing design of cars to handle the fuels, and a nod to the corn farmers in the Midwest, we may be seeing E15 more widely available in the near future.

An interesting side effect of ethanol use is also being discovered at petroleum cleanup sites. The subsurface geochemistry at a site is a key factor in assessing the source of a release, the speed and extent of contaminant migration, and appropriate cleanup options. Additives such as lead and MTBE have always provided clues as to the age, degradation, and source of releases. But now, in addition to differentiating fuel sources, environmental scientists are recognizing the impact that higher versus lower percentages of ethanol can have on subsurface geochemistry at spill sites, and that ethanol can actually create conditions for increased mobilization of contaminants in the environment. More specifically, studies indicate that ethanol significantly increases the solubility of petroleum constituents in water, which can have several effects at spill sites: