About a week after a judge disqualified the State of Minnesota’s legal counsel from a longstanding pollution case against Maplewood-based 3M Company, the disqualified firm and the state are appealing the decision.

The state sued 3M in 2010 over alleged damage caused by the company’s disposal of chemicals called perfluorochemicals (PFCs). 3M used PFCs in the production of several consumer, commercial, and industrial products, and the lawsuit claims that decades of disposal of PFC waste in Minnesota polluted ground and surface water.

But in July, 3M sued the state’s law firm, Washington, D.C.-based Covington & Burling, LLP, stating that the firm had worked with 3M for more than a decade on issues pertaining to its fluorochemical business, which involved PFCs, and requesting that the firm be disqualified from the case.

3M alleged that Covington “breached its duties to 3M” by “switching sides.” The firm went from arguing that trace amounts of PFCs did not pose a risk to humans to arguing that exposure to those same chemicals is dangerous, 3M said.

In a letter to the judge overseeing the environmental case between the state and 3M, Minnesota Solicitor General Alan Gilbert questioned why 3M waited 17 months after the original complaint was filed, and until more than 6 million documents had been exchanged, before filing its motion. He also said that 3M made its move “shortly after recent incriminating testimony by 3M employees.”

Hennepin County District Judge Robert Blaeser, however, ruled last week in favor of 3M, granting the company’s motion to disqualify Covington. In his 14-page order, Blaeser said that Covington, during its representation of 3M, “received privileged and confidential information from 3M” that was relevant to the state’s case against the company, and “Covington did not disclose the nature of its conflicts to 3M.”

Following the judge’s ruling, Timothy Hester, chairman of Covington’s management committee, said in a statement that the firm disagreed with the decision. Spokespeople from both Covington and Minnesota’s Attorney General’s office said Wednesday that the parties have filed notices of appeal with the court.

“3M was a former Covington client when we took on the representation of the state (itself a long-time client), and the prior representation identified by 3M was not substantially related to the new matter, and, in any event, 3M waived any right to seek disqualification by its unjustified 15-month delay in objecting,” Hester said in a Wednesday statement.

William Brewer III, a partner at Dallas-based law firm Bickel & Brewer and lead counsel for 3M, said in an e-mailed statement that 3M is “confident that the court’s decision will be upheld.”

“In 3M’s view, there is no question Covington was properly disqualified from representing the State of Minnesota,” he said.