MONTPELIER — The U.S. Environmental Protection Agency may reconsider its approval of the rules governing wastewater treatment plants and other sources of pollution that flow into Lake Champlain.

The move could have a major impact in Vermont, leading to stricter rules on wastewater treatment and phosphorous discharges into waters that lead into the lake.

EPA regulators told a federal court this week that they will reconsider approval of the state's "Total Maximum Daily Load," or TMDL, rules approved in 2002 in conjunction with the EPA. TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet water-quality standards.

The decision is more than legal jockeying among government agencies: A change in those rules – if they end up being rewritten – could eventually have an effect on virtually every town or city in the Lake Champlain watershed, and therefore the bulk of the population in Vermont. The rules are a critical part of what governs wastewater treatment plants and other sources of phosphorous pollution of the lake.

Gov. James Douglas reacted strongly Tuesday, saying the federal regulators are jeopardizing what he believes is a successful effort to clean up Lake Champlain. The EPA filing was made as part of a court case brought against the federal agency by the Conservation Law Foundation environmental organization.

"They have sent signals … that they want to reopen the TMDL. I don't understand why they are giving this any credence," Douglas said. "We have been working on the basis of this plan for all of this time."

Douglas said federal regulators should not be taken aback that the cleanup of the lake is taking time.

"They recognized clearly and in writing in 2002 that this would be a long-term proposition," Douglas said. "It shouldn't be a surprise."

But in a statement explaining its decision to consider reopening the TMDL, the federal regulators disagreed.

For one thing, the TMDL will be re-evaluated in 2013 in any case, so it does not make sense to vigorously defend the pollution plan from the CLF lawsuit.

"Regardless of the merits of the TMDL at the time it was issued, it is now eight years old, and it was based largely on data from 1991," according to the agency. "A re-evaluation offers the opportunity to consider more recent data on precipitation trends and associated increased tributary flows and phosphorus loadings."

More rainfall was one of the reasons the Conservation Law Foundation filed its lawsuit challenging the validity of the pollution reduction plan in the first place. That lawsuit was filed – and separate challenges to wastewater treatment plant permits including in St. Albans and Montpelier – after CLF tried unsuccessfully several years ago to convince lawmakers to reopen the TMDL rules. In part that effort was defeated when municipalities objected to redrafting the rules.

"The governor seems to want to defend a record on Lake Champlain that just isn't borne out by the facts," said Chris Kilian, the head of CLF's Vermont office. "The governor can't really create a legacy of cleaning up Lake Champlain by fighting to keep a flawed cleanup plan in place."

"EPA recognizes that its charge is to protect the waters of the United States," Kilian said. "We know that the underlying assumptions of the TMDL are no longer accurate."

If the EPA reopens the TMDL rules, it could mean that wastewater treatment plant permits and other regulation of discharges of phosphorous – including from farming – will have to be more strict as they come up for renewal or review, a process that typically happens every five years or so.

"It means a big unknown at this time, for us, for folks who have facilities," Vermont Agency of Natural Resources Secretary Jonathan Wood said.

"Potentially permits that have been issued don't have the force of law anymore," he added. "That is the specter that is raised here. That's why this is so big."

But Kilian said his organization cannot allow a TMDL that is based on outdated information to continue if it results in a more polluted Lake Champlain.

"We can't sit idly by and allowing more phosphorous pollution to be dumped into this lake," Kilian said.