LAFAYETTE — The battle over the proposed expansion of a natural gas storage operation under Lake Peigneur is headed to court.

Save Lake Peigneur, the Louisiana Environmental Action Network and lake-area resident Roger Stelly have filed a lawsuit to void a permit the state Department of Natural Resources granted last month for the project.

AGL Resources is proposing to scour out two new salt caverns for its Jefferson Island Storage & Hub facility, expanding on the two existing caverns that have been used for gas storage in the salt dome under Lake Peigneur since the 1990s.

The permit granted by DNR last month was the first of three state permits needed for the expansion, which residents living around the lake have fought against for several years.

“It’s too bad that we have to sue to get results,” Save Lake Peigneur President Nara Crowley said Tuesday. “It would be wonderful if the state would do the right thing on its own for a change.”

The lawsuit, filed last week in state court in Iberia Parish, argues that DNR did not adhere to a legal standard that requires the agency to carefully consider the environmental impacts of a project.

“DNR maintains that its Office of Coastal Management staff followed the applicable permitting rules procedures and conducted the process appropriately, with potential environmental impacts to the coastal wetlands area being the primary consideration,” DNR Communications Director Patrick Courreges said in a statement.

The state permit at issue in the litigation is for dredging that needs to be done to bring equipment into Lake Peigneur for the expansion project, and DNR’s formal review of that permit focused on the effects of the dredging itself, not the larger project.

DNR officials stated in the permit approval documents that concerns about the overall project will be taken into consideration when the agency reviews the two additional state permits required for the project.

AGL, which defends the proposed expansion as safe, still needs a permit to scour out the caverns in the salt dome and another to store natural gas in the newly scoured-out caverns.

Opponents have raised concerns about the project compromising water quality in the Chicot Aquifer and about safety, pointing to the large sinkhole in Assumption Parish that is believed to be linked to a collapsed salt cavern.

The lawsuit states that there have been 80 documented episodes of bubbling at Lake Peigneur since 2006, similar to the bubbling that occurred in and around Bayou Corne before the sinkhole developed last year.

There have been five episodes of bubbling at the lake this year, according to the lawsuit.

DNR has investigated the reports of bubbling at Lake Peigneur but has reached no conclusion on the cause.