With gasoline pushing up to and past $4 per gallon in Illinois, this is an opportune time to re-think our driving habits. But from an environmental perspective, it's always a good time to look at ways to use less gasoline. The less we use, the less the potential for pollution of water supplies from gasoline compounds.

The most common contaminants from gasoline are aromatic compounds, specifically the BTEX compounds (benzene, toluene, ethylbenzene, and xylene). Remember the smell of airplane glue? That’s toluene. It addition to being volatile, they are some of the most soluble compounds of gasoline (which is made up of 100’s of different types of organic molecules) and thus a particular problem in groundwater. Gas well explosions such as the Horizon Deepwater disaster in the Gulf of Mexico last year grab our attention, but groundwater supplies are continually being polluted by gasoline from pipeline breaks or leaky underground storage tanks (LUSTs). One estimate is that, of about 1 million underground storage tanks sites in the U.S., 500,000 have had leaks.

In additional to the molecules naturally found in petroleum, refiners introduce additives to improve engine performance and reduce knocking. For many years the additive of choice was tetraethyl lead, which was an environmental disaster. I’m old enough to remember leaded gasoline and the unhappiness of many people when the then young Environmental Protection Agency forced the removal of lead from all gasoline in the U.S.

After lead was banned, refiners began using methyl tertiary-butyl ether (MTBE) instead. It worked great, helping improve air quality and reducing smog in many cities. Unfortunately, it has the unfortunate property of being very soluble and slow to break down. Once leaked into the environment, it could be transported great distances, much further than the BTEX compounds which were much more degradable. In 1988, a pipeline break near Kankakee discharged 120,000 gallons of gasoline; 6 years later MTBE turned up in two nearby public water supplies, and also in some domestic wells. MTBE had turned up in 26 public water supplies in Illinois as of 2000. In 2001, Illinois instituted a partial ban on MTBE in gasoline.

So now we primarily use ethanol. That sounds pretty harmless, right? Unfortunately ethanol may actually increase smog. Although from a groundwater perspective, ethanol is not a problem, being highly biodegradable.