More than three years after Minnesota Attorney General Lori Swanson sued 3M Co. over PFC pollution damages, the state’s case is at a ­crucial pivot point, at risk of having to start from scratch.

The state Supreme Court on Monday will hear arguments with high stakes for both sides: whether the state can keep using Covington & Burling, the Washington, D.C., law firm that took the case on a contingency basis in December 2010.

The hearing comes after the state Court of Appeals in July affirmed Covington’s disqualification for violating professional rules of conduct in failing to properly notify 3M that it was representing the state in its suit. Covington had represented 3M on PFC-related regulatory matters before taking the state’s case on the opposing legal side, creating a conflict of interest, the appellate court ruled. The state is contesting that decision.

The issue has essentially been a lawsuit-within-the-lawsuit, taking more than a year and a half and waylaying the state’s efforts to press its claims against 3M that it damaged the environment by its dumping of PFCs at several legal and permitted east metro sites. PFCs, or perfluorochemicals, are a family of compounds made by 3M over five decades until 2002, but still made by other companies and used in a vast array of consumer and manufactured goods. Among its claims, the state says the water supply for more than 125,000 people in the Twin Cities area has been contaminated.

A trial, expected to hinge on the disputed health effects of PFCs, was to have taken place last July. “We would be done by now,” said Alan Gilbert, the state’s solicitor general.

Gilbert acknowledged that the state was blindsided by 3M’s move to disqualify Covington & Burling 15 months into the case. But that delay also is part of the argument the state plans to make for keeping the law firm. 3M, in defending the timing of its move, countered it had not realized the extent of Covington’s legal involvement with PFC-related issues.

Gilbert declined to speculate on what is to happen if Covington is disqualified. But in briefs submitted to the court, the state says that, even if it were to find a new law firm with Covington’s expertise willing to work on a contingency basis, the litigation “may well have to start over.”

Millions of dollars have been expended in the legal clash, and millions more are at stake. The state’s contingency deal with Covington has provisions for a potential settlement exceeding $150 million, ­documents show.

But the case isn’t about money, Gilbert said. It’s about holding 3M legally accountable for damage to the state’s natural resources and potential future damages as more is learned about the extent of harm posed by PFCs.

The state’s case cites studies by a scientific panel created in 2005 following a $235 million settlement in a class-action lawsuit brought by citizens against chemical giant DuPont involving PFC contamination of drinking water in the Ohio River Valley. It found “probable” or “possible” links between the compound and several diseases, including testicular and kidney cancer, thyroid disease, pregnancy-induced hypertension, ulcerative colitis and ­elevated ­cholesterol.

Other studies cited by the state have found that children exposed to PFCs by eating fish had less protection from immunizations.

In simplest terms, said Ben Wogsland, spokesman for the attorney general’s office, the case comes down to the familiar sign found in a pottery shop: “You break it, you pay for it.”

“This case is really about what 3M broke,” he said, which includes polluting four aquifers, a 139-mile stretch of the Mississippi River and more than dozen lakes.

The question of harm

William A. Brewer III, 3M’s lead attorney in the case, adamantly defended its long-held assertion that PFCs, such as the common types PFOA and PFOS that have been detected in the east metro, cause no harm to people at levels typically found in the environment.

“The state’s case is built on an incorrect premise,” he said. “PFCs such as PFOS and PFOA are not hazardous — there are just no [negative health effects] from environmental exposure to these compounds. The state’s case boils down to the allegation that the mere presence of PFCs in the environment equals harm.” That claim won’t hold up under legal scrutiny, he said.

When pressed in pretrial documents, the state admitted that it “cannot identify a single instance where exposure to PFCs in the state’s waters proximately caused an adverse effect in any person.” Even officials with the Minnesota Department of Health, in a 2012 assessment, “concludes that, currently, drinking water from public or private wells that contain PFCs is not expected to harm people’s health.”

There are other problems with the state’s allegations, Brewer said, adding that 3M has acted responsibly, spending about $100 million in remediation work in Cottage Grove, Oakdale, Woodbury and Lake Elmo. “We wouldn’t be involved in the case if we didn’t believe 3M was right,” he said.

Likewise, Gilbert said the state is hoping to get its case back on track because the impetus for bringing the suit hasn’t changed: to keep 3M’s feet to the fire to clean up PFCs. He added: “These compounds are going to have a direct effect on the state’s natural resources for a long period of time.”