The Environmental Protection Agency is conducting two broad investigations into possible violations of federal air pollution regulations by a "significant" percentage of the nation's 160 oil refineries, a senior agency official said today.

At issue in the probes is whether refineries have under-reported what are known as "fugitive" emissions of volatile organic compounds from valves and pipes, and whether they have installed new refining units that increase emissions without meeting legal requirements to offset emissions elsewhere or install new pollution control equipment.

Facilities that are found to have violated the Clean Air Act are subject to penalties of up to $27,000 per day.

The probe into fugitive emissions has uncovered 17 refineries that were emitting more pollution than their monitoring programs reported, in some cases by a factor of four. Enforcement actions--which can include lawsuits--are expected to be taken against several of those unnamed refineries, said the official, who requested anonymity.

A second ongoing investigation into the suspected failure of refineries to offset increased pollution coming from the installation of new refining units has revealed what the official said was likely "a widespread" problem.

"Our initial investigation showed [plants] are making a number of modifications without going through the permit process and putting on pollution control equipment," said the official, adding that of those refineries investigated so far "a very significant percentage" would likely be subject to enforcement actions by the EPA.