MTBE has been called “the Houdini of pollutants.”

The gasoline additive is a colorless, odorless, tasteless carcinogen that slips into groundwater, where it can remain undetected for years.

But if the Senate approves the federal energy omnibus bill, passed Tuesday by the House of Representatives, those whose drinking water has become contaminated with the chemical could lose the right to sue its manufacturers.

Nationwide, more than 9,000 wells in 31 states are believed to be contaminated with the chemical, according to a 2000 study.

Here in Maine, a 1998 study indicated that at least 16 percent of the state’s public water supplies, and more than 900 private wells have become contaminated since the state began using the gasoline additive.

In 2001, five southern Maine homeowners won a $35,000 settlement for their contaminated water. That may be the state’s one and only such suit if, as anticipated, the energy bill is signed into law by President George W. Bush before Thanksgiving.

This debate pits environmental goals against each other, because MTBE – methyl tertiary-butyl ether – was originally intended to reduce air pollution. MTBE increases the octane rating of gasoline, as well as its oxygen content, which means that motorists get an efficient fuel that burns more of the chemicals that would otherwise become air pollution.

“You’re having fewer nasty byproducts come out of the tailpipe,” said John Peckenham, a research scientist at the University of Maine at Orono Mitchell Center, who is working on a study of MTBE’s impacts in Maine.

Nationwide, about a third of all gasoline sold contains additives to address air pollution problems. Eighty percent of the time that additive is MTBE, according to the federal Environmental Protection Agency.

After joining the EPA’s reformulated gasoline program, Maine in 1994 began selling gasoline with a high MTBE content throughout the state’s seven southernmost counties, where air pollution levels have exceeded federal standards for ozone pollution.

As far as air pollution is concerned, the system worked, according to the state Department of Environmental Protection. Air quality improved almost immediately with visible decreases both in ozone pollution and in the presence of toxic chemicals from gasoline in the air.

But soon thereafter, reports of MTBE contamination in groundwater began coming in from all over the state, the DEP said.

Several late 1990s studies indicated that dozens of wells were contaminated with low levels of the contaminant, even in areas far from stations that sold reformulated gasoline.

“It’s fairly widespread,” Peckenham said Wednesday. “The only way to keep MTBE out of the groundwater is to keep it out of the gasoline.”

Today, Maine purchases a specially blended fuel, primarily from Irving, which contains between 2 percent and 3 percent MTBE, on average. Reformulated gasoline contained about 15 percent MTBE, according to the DEP.

But the groundwater contamination remains.

Other states have found similar pollution, with 24 choosing to ban MTBE altogether. Dozens of towns, states and even a small Catholic school in Connecticut have filed lawsuits, seeking funds to clean up their MTBE pollution problems.

A California utility district won a groundbreaking $50 million settlement last year on the argument that MTBE producers had put a defective product into the marketplace. In mid-October, New Hampshire sued 22 oil companies on the same grounds, seeking millions of dollars to clean up MTBE pollution that has contaminated a third of the state’s water.

But petroleum industry spokespeople like Frank Maisano, a Washington D.C.-based lobbyist, argue that they were forced by regulation to use MTBE and are now being punished for doing so.

“The product defect argument is frivolous,” he said Wednesday.

“MBTE does what it was intended to do,” Maisano said, citing air quality improvements.

Leading Republicans, particularly House Majority Leader Tom DeLay of Texas, say that the protection is vital to stop lawyers “on a rampage.”

Most of the plants that produce reformulated gasoline with MTBE are located in Louisiana or in DeLay’s and Bush’s home state of Texas, leading some Congressional Democrats to criticize the MTBE liability protection as “a get out of jail free card” for campaign contributors.

The reformulated gas companies could have chosen other ways to meet the EPA air quality rules, such as increasing the use of ethanol, but petroleum interests lobbied heavily for MTBE because it was the easiest, cheapest option, critics of the liability protection have said.

Maisano argues that the high cost and low availability of ethanol made MTBE the only viable option.

Even Peckenham concedes that the issue is politically and economically complex. He is working with fellow researchers to determine whether MTBE’s groundwater risks outweigh the health and environmental benefits that it brings to the air.

But regardless of who is to blame, the nation is struggling with a tremendous MTBE contamination problem that must be addressed, he said.

The U.S. Conference of Mayors estimates that MTBE cleanups nationwide could cost more than $29 billion. Fears that states and municipalities will be saddled with the cost decided the issue for Maine’s delegation.

Maine Sens. Susan Collins and Olympia Snowe have broken with the Republican party to speak out against the MTBE liability protection. Both have pledged to vote against the energy bill unless it is substantially improved.

Maine Reps. Tom Allen and Michael Michaud both voted with the majority of their Democratic party, unsuccessfully opposing the House bill Tuesday.