Wal-Mart's plans to expand its Rohnert Park store were set back Thursday after a Sonoma County judge ruled in favor of a challenge to the City Council's approval of the project.

Judge Rene Chouteau ordered sections of the project's environmental impact report dealing with traffic mitigation and noise to be redone.

But it was hardly a complete victory for Wal-Mart's opponents, who filed the lawsuit against the city in September.

The decision dismissed a central complaint by the plaintiffs, the Sierra Club and Sonoma County Conservation Action, that the council did not have the authority to approve the project.

And it did not address another key argument by opponents that the project violated the city's general plan.

"I was a little concerned that the substantive issues don't seem to have been dealt with," said Rick Luttmann, a Sonoma State University math professor who helped work on the general plan.

"We're not worried about the EIR per se, we are worried about the project, so we'll have to see," Luttmann said.

Still, the ruling effectively stretches out the process for Wal-Mart, which has tried for two years to make its Redwood Drive store a superstore by adding a grocery.

"I see it as a win along the campaign trail," said Dennis Rosatti, executive director of Sonoma County Conservation Action.

It was one of a number of groups that opposed the project, which the council approved on a 4-1 vote in August. That decision overturned the city's planning commission's earlier rejection of the application, infuriating critics.

"We haven't stopped it, but we've put up multiple roadblocks," said Marty Bennett, a Santa Rosa Junior College history instructor who helped build the coalition of labor and environmental groups that opposed the expansions.

Wal-Mart spokeswoman Tiffany Moffatt said the company is "currently reviewing the ruling to determine its impact."

Attorneys for Rohnert Park, which could appeal the ruling, did not respond to requests for comment Thursday.

Councilwoman Pam Stafford, who voted in favor of the project, said she hoped Wal-Mart would continue steps to complete the expansion.

"I'm disappointed because they had a legitimate right to add the grocery store," she said, "and I think the EIR did address those issues."

In 2009, groups opposed to a Wal-Mart in Roseland won a legal challenge to the Santa Rosa City Council's approval of the environmental impact report on the project. Wal-Mart then abandoned its five-year bid to open the store.