Even with work on the Interstate 69 extension proceeding  in earnest downstate, environmental and citizens groups are suing to stop construction of the 142-mile link between Evansville and Indianapolis.

The complaint filed this week in U.S. District Court by Hoosier Environmental Council and Citizens for Appropriate Rural Roads seeks to overturn a permit the Army Corps of Engineers issued for the $3 billion project.

The groups say the permit authorized the Indiana Department of Transportation “to destroy valuable natural resources” by rerouting streams and filling wetlands in the path of the new highway in Daviess and Greene counties.

They contend the Army Corps of Engineers never completed an independent alternatives analysis for the route, such as improving existing U.S. 41 and I-70. Such a route would cost $1 billion less and reduce environmental damage by 60 percent, they claim.

“If our action is successful, the state of Indiana will have to consider alternatives to the chosen route that have less environmental impact on rivers and wetlands,” said Tim Maloney, senior policy director of HEC.

The odds of halting work on the new terrain route appear steep, however. INDOT’s contractors have completed a 1.7- mile stretch of I-69 northeast of Evansville. It’s part of a $700 million segment from Evansville to Crane that’s scheduled for completion next year.

INDOT officials said they had yet to review the lawsuit and declined comment.

An opponent of such a project might use a strategy such as seeking a temporary restraining order, although “you’d have to really show injury” in federal court to succeed, said John Krauss, a professor of public and environmental affairs and adjunct professor of law at IUPUI.

The controversial I-69 extension faces other challenges down the road, including a lack of funding for the section between the Bloomington area and Indianapolis, and for much of the stretch north of Crane. The southernmost section is being funded in part from proceeds of the $3.8 billion lease of the Indiana Toll Road.

INDOT has been trying to stretch its funding by deferring some overpasses and rest stops, and has invited contractors to offer bids using asphalt as well as the concrete that’s traditionally considered superior for new-terrain interstates. Other ideas include thinner pavement in shoulders and passing lanes.

HEC and Citizens for Appropriate Rural Roads also say the new-terrain route poses particular environmental dangers in the hilly region near Bloomington. Last March, the U.S. Environmental Protection Agency told INDOT that “streams and karst features are resources of concern.” Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble bedrock.

“Construction may have started, but it is unlikely I-69 will ever be finished unless INDOT diverts a major share of the state’s dwindling highway dollars away from badly needed road and bridge repairs around the state,” CARR president Thomas Tokarski said in a statement.