Several studies on the potential cleanup costs of MTBE contaminating drinking water sources reveal wide differences in the perceived threat the substance presents to human health.

MTBE has been added to gasoline since 1979, first to prevent knocking after prohibition of leaded gasoline took effect and later as an oxygenate that allowed more complete combustion and hence a lower level of polluting tailpipe emissions. But MTBE is extraordinarily mobile if it leaks from underground storage tanks, much more so than other gasoline constituents. The result is that MTBE has been found in ground water used as drinking water sources.

The contamination is so advanced, according to two studies sponsored by the American Water Works Association and the Association of Metropolitan Water Agencies (AMWA), that costs to remove MTBE from drinking water systems across the country will range from about $30 billion to $85 billion. The studies point out that much of the current attention on MTBE focuses on cleaning up areas around leaking underground storage tanks (LUST). This avoids the problem of ground water contamination more removed from the area of tanks.

"Leaking underground tank remediation and water supply cleanup require different solutions, so the LUST program will do little or nothing to clean up public drinking water wells," said Diane VanDe Hei, AMWA's executive director.

The dollar signs provided by the water associations were fewer in a study released shortly afterward by the American Petroleum Institute (API).

According to API, MTBE is rarely present in private wells in concentrations that would require treatment. API quotes a statement by the U.S. Geological Society, which said that it has not found widespread high-level MTBE contamination in rivers, reservoirs and ground water that are actively used as sources for community water systems.