Austin environmental groups filed dueling federal lawsuits against the Texas Department of Transportation this week, aiming to halt or rework an Oak Hill highway expansion they fear will be environmentally damaging.

The Save Our Springs Alliance on Monday sued both TxDOT and the U.S. Fish and Wildlife Service, saying the proposed expansion of the U.S. 290 and Texas 71 interchange could threaten local salamanders. The suit accuses the entities of abandoning due diligence in their environmental mitigation planning. The alliance fears runoff will increase and harm the endangered Austin Blind Salamander or Barton Springs Salamander, according to the suit.

The alliance is asking a judge to halt the Oak Hill project until TxDOT's compliance with the Endangered Species Act can be proven in more detail.

Meanwhile, a coalition of environmental and neighborhood groups leaped into the action Tuesday with a lawsuit targeting TxDOT and the Capital Area Metropolitan Planning Organization. That suit argues the project will harm water quality and be a noisy nuisance to neighbors. It asks to halt the project until further analysis is done. The coalition's lawsuit argues the large scope of the expansion came from flawed analysis. It argues its potential impacts on the surrounding area violate the National Environmental Policy Act and National Historic Preservation Act.

The groups, which included Save Barton Creek Association and Fix 290, filed the suit without a lawyer. They said in a news release that they don't wish to stop the project, but to work with TxDOT to improve it.

BACKGROUND: Major interchange project ahead for the “Y” in Oak Hill

The $550 million Oak Hill "Y" project has been long planned to build an interchange at the oft-congested intersection of U.S. 290 and Texas 71. After years of being stalled, the project has moved quickly forward this year with a financial push from the city of Austin to help TxDOT begin acquiring right-of-way and picking a contractor.

TxDOT ranks the intersection the 53rd most congested in Texas. Plans call for turning that stretch of U.S. 290 into an elevated road similar to Texas 71 along Ben White Boulevard in south-central Austin. After breaking from Texas 71, U.S. 290 would go west along a sunken trench. Two flyover bridges would connect U.S. 290 to Texas 71 where the highways merge, and frontage roads will flank both highways. In some spots, there would be up to 12 lanes of roadway.

Austin Council Member Paige Ellis, whose District 8 includes the roadway, did not return phone calls to comment on the lawsuits Tuesday. Ellis voted with the majority of her council colleagues earlier this year to kick in $3.3 million to help the highway project get started faster.

The Save Our Springs Alliance argued that, despite TxDOT assurances of mitigation, ground excavation and runoff from more lanes of concrete is sure to harm the area's sensitive Edwards Aquifer recharge zone and send more sediment downstream to the salamanders. The alliance's lawsuit notes that TxDOT has said it has new methods of reducing the runoff of solids to below even current levels. But the suit registers skepticism at that, pointing to changing TxDOT communications on the subject. It argues U.S. Fish and Wildlife has let the agency get away with a lack of plan specificity.

"In terms of environmental sensitivity, there couldn't be a worse location for this amount of excavation," SOS attorney Kelly Davis said in a statement Tuesday. "The Recharge Zone is highly vulnerable to pollutants, such as silts and fuels, which can impact the underground water quality upon which the endangered salamanders depend."

TxDOT spokeswoman Veronica Beyer said the agency does not comment on pending litigation. Authorities at CAMPO did not respond to requests for comment.

RELATED: Judge tosses challenge to Texas 45 Southwest, South MoPac toll lanes

The Save Our Springs Alliance has been vocally opposed to the highway expansion in general, arguing that instead of a highway expansion, the region should build a secondary meandering boulevard offset by parks. The alliance also has sued in the past to try to stop construction on MoPac and Texas 45 Southwest.

Robert Tobiansky, a former transportation committee chairman for the Oak Hill Association of Neighborhoods, lives near the Y and said something must be done about the bottleneck there.

The alliance, Tobiansky said, perpetually tries to halt any change in the city.

"They're basically a no-growth group, and they don't want anything built and they just can't get over that this highway is going to get built," he said. "I've been working for the last five years to get this highway built. ... The transportation is needed."