Attorney General Lori Swanson and the Washington, D.C., law firm she hired to pursue a pollution case against 3M both have appealed a Hennepin County District Court ruling last week that disqualified the firm because of its past representation of the Maplewood-based manufacturing giant.

Attorneys for Swanson and Covington & Burling filed separate requests with the Minnesota Court of Appeals late Tuesday to overturn the ruling of Judge Robert Blaeser.

The court motions said 3M's disqualification request should not have been granted because it came more than 15 months after Covington & Burling became the state's counsel of record.

The state alleges in its case that 3M contaminated groundwater sources and stretches of the Mississippi River over 50 years through the release of perfluorochemicals (PFCs).

"3M raised no objection to Covington's representation of the state of Minnesota in this action until March 2012, when the parties had already engaged in substantial discovery, which included producing and reviewing approximately six million documents and taking 50 depositions," the state's notice of appeal said. "The effect of the ruling ... is to reward 3M for an inexplicable sixteen-month delay."

3M contended that Covington & Burling had a conflict of interest in the pollution case because the law firm advised 3M on food packaging matters involving the use of PFCs in the 1990s.

Blaeser agreed with 3M and said Covington & Burling violated Minnesota rules of professional conduct in a "conscious disregard" of obligations to 3M as a former client.

Timothy Hester, chair of Covington's management committee, said the firm and the state will seek an expedited review of its appeal.

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

Counsel for 3M, Bickel & Brewer of Dallas, said it is confident the district court ruling will be upheld. "In 3M's view, there is no question Covington was properly disqualified from representing the state of Minnesota," said William Brewer III, a partner with the firm.

David Phelps • 612-673-7269