The U.S. Environmental Protection Agency has ruled that several changes to Montana’s water quality standards passed in the 2021 legislative session do not comply with the federal Clean Water Act, asserting in a letter sent to state officials this week that previously approved standards are on the books until the feds say otherwise.

The changes to nitrogen and phosphorous pollution standards were not only adopted without proper review by EPA, whose authority supersedes the state’s when dealing waters subject to the Clean Water Act, but also could lead to degradation of Montana’s waterways, the regulator wrote in its May 10 action letter.

It’s not yet exactly clear how EPA’s actions will affect the ongoing process to replace the state’s existing numeric nutrient criteria with broader, more flexible narrative criteria, only that this development ensures numeric criteria remain in place for now. The numeric standards, EPA wrote, are scientifically defensible and protective of designated uses of waterways.

“EPA is not aware of any information demonstrating that the science has changed to alter this conclusion,” the letter to DEQ Director Chris Dorrington states.

A spokesperson for the Montana Department of Environmental Quality, which under Senate Bill 358 must replace the old standards, said the agency is still reviewing the impact of the letter on the state’s implementation of new water quality standards, a rulemaking process that has been playing out for months under the auspices of a stakeholder body called the “Nutrient Work Group.” DEQ will discuss the letter at the work group’s next meeting on May 17.

Nutrient pollution impairs 35% of river miles in the state. Eutrophication, or an overabundance of nutrients, can kill fish and create water conditions that are even potentially harmful to humans.

The EPA for years urged states to adopt numeric criteria as the best way to protect river health from nutrient loading, something Montana did in 2014. The standards govern discharge permits to point-source polluters like sewage treatment plants, municipal governments and others.

Regulated entities in Montana argued numeric standards were too costly to meet with current technology, leading lawmakers — mostly Republicans — to push for a removal of the numeric standards in favor of a watershed-specific “adaptive management program” that prioritizes more affordable phosphorous reduction and assesses the impact of nutrient loading through monitoring, rather than precise measurements of nutrient contamination taken at the source.

The bill directed the Montana Department of Environmental Quality to develop rules to implement the transition, but also stipulated that until that happens, DEQ was to administer its discharge permitting program following the intent of the bill.

However, that legislation was an unauthorized revision that conflicted with the Clean Water Act, which requires the EPA to approve state and tribal water policy changes, the federal regulator ruled.

The EPA took issue with four provisions in the bill: the section establishing an immediate effective date, two sections directing the state to remove reference to the numeric standards from rules, and a section that creates a de minimis exemption from the nutrient criteria under certain conditions, something that “could allow degradation of high-quality waters,” the letter said.

The agency’s action comes amid litigation from a Montana water quality advocate alleging that EPA has been delinquent in recognizing that the changes in SB358 constitute unlawful revisions to water quality standards. Guy Alsentzer, executive director of Upper Missouri Waterkeeper, the organization that filed the suit and a member of the Nutrient Work Group, said the EPA’s letter affirmed that DEQ has no adequate basis for relying solely on narrative standards.

The state has argued in response to concern from groups like Alsentzer’s that it had yet to formally submit revised standards, and that it wouldn’t do so until rulemaking was complete by this fall. But EPA said in its letter that it does not need the state to submit revisions for the federal government to act on them.

“EPA is disapproving these provisions because the revisions are not consistent with the requirements of the CWA,” the letter reads.

Alsentzser said DEQ should heed EPA’s letter as it continues the rulemaking process under SB358, should that process continue at all. Instead of removing numeric standards, though, Alsentzer said that DEQ should focus on developing durable, scientifically sound nutrient standards for both point source and non-point source pollution like septic runoff.

“If there’s any effort to go forward with putting in front of EPA this fall a proposal to strip numeric nutrient criteria, boy, buckle up,” he said.