Environmental Progress - Spring 2000

MTBE: Good News / Bad News Additive

Good news for air quality is not-so-good news for groundwater

Most people agree that protecting and improving the air, land and water around us is a worthwhile goal, but the road getting there isn't always a neat and direct line. Recent detections of a worrisome gasoline additive in groundwater supplies around the nation, including a handful in Illinois, underscore how tricky it can be sometimes to achieve the necessary balance. The substance is methyl tertiary butyl ether (MTBE) and it's getting into our water because we want clean air.

In the 1970s some producers began adding MTBE to gasoline as an octane enhancer. A natural gas derivative, MTBE makes gasoline burn cleaner by boosting oxygen. It is highly soluble in water and once introduced, can spread rapidly through an aquifer.

Some 20 years later, as part of a Clean Air Act effort to reduce unhealthy smog levels near some major metropolitan areas, U.S. EPA mandated use of reformulated gasoline in these localities. MTBE quickly became the first choice as an additive. The only real alternative contender was ethanol, a corn derivative that was the additive of choice in corn producing states like Illinois.

By the end of 1997, about a third of all gasoline nationwide met the specifications to be classified as reformulated, and 84 percent of that fuel contained MTBE. It was in use in 32 areas of 18 states. About the same time, some of those states began detecting MTBE in drinking water sources, usually in groundwater but sometimes in surface water as well. Both its prevalence and the detection levels generated such serious concern in California that the governor there has, by executive order, directed its use be phased out in the next couple of years.

MTBE has been found in 26 Illinois community water supply wells.

Illinois, by comparison, has so far had detections in only 26 of the nearly 1,800 public water supplies that the IEPA regulates, and the majority of them have been at very low detection levels. These 26 detections were in groundwater. One surface supply had a single detection but it was never repeated. Some groundwater detections have been intermittent, showing up once or a few times, then disappearing without being detected again.

Illinois EPA Director Tom Skinner credits the state's ethanol use as a key factor in the comparatively low number of "hits" in a heavily populated and heavily traveled state that includes Chicago and part of the St. Louis metropolitan area within its boundaries.

"The presence of any contaminant in our water supply sources is a matter for concern," Skinner said. "But use of ethanol rather than MTBE appears to have helped clean the air in our densely populated metropolitan areas while avoiding the related groundwater contamination problems that are now worrying other states."

During testimony before the U.S. House Committee on Commerce's subcommittee on Health and Environment in early March, Skinner urged the committee to not overreact to the MTBE threat by removing the oxygenate requirement entirely, as some legislation has proposed. He noted that reformulated gasoline blended with ethanol has significantly contributed to cleaner air in the Chicago metropolitan area and urged that those benefits should be allowed to continue.

Taste and odor complaints kick in first

There are currently no MCLs (maximum contaminant levels) for MTBE in drinking water though studies are underway at the federal level to more specifically determine its human health impacts. Though data is lacking to clearly label MTBE as a human health risk, it is considered a possible human carcinogen. However, because at levels as low as 20 to 40 parts per billion (ppb) water contaminated with MTBE has a strong turpentine-like taste and odor, consumers might reject using it even at levels that would not be considered harmful.

Testing for MTBE is not currently required

In the absence of a federal or state MCL for MTBE, there is no requirement that labs test for its presence in drinking water samples. Since 1997, MTBE has been included among volatile organic compounds targeted in potable water testing done by the Illinois EPA laboratories for the state's optional community water supply laboratory fee program. More than 95 percent of the community water supplies in Illinois are enrolled in that program. The rest use certified laboratories of their own choosing, and may or may not request MTBE testing.

Of the detections in Illinois public water supply wells, nearly all were well below the taste and odor detection levels, but wells contaminated with MTBE have been taken out of service in three Illinois communities because levels were high enough to be offensive to users. Individual wells were affected at Island Lake, in northeastern Illinois, and at East Alton, located on the Mississippi in the west central part of the state. In Kankakee County, Oakdale Acres subdivision was forced to shut down its entire groundwater system and connect to a nearby community's public water supply, after a pipeline rupture contaminated the subdivision's aquifer.

Responding to national concerns, U.S. EPA Administrator Carol Browner and U.S. Agriculture Secretary Dan Glickman jointly announced in March that U.S. EPA will order the phase-out of MTBE as a substance that poses a public threat.

A full ban could take several years to implement, and Browner urged Congress to act to amend the Clean Air Act promptly, specifically urging Congress to ban MTBE but require fuels to include a small amount of ethanol or other bio-fuels made from agricultural products such as rice straw in California.