Sen. Lamar Alexander and other lawmakers see an avenue to enact the “most important piece of legislation for national parks in decades,” the Tennessee Republican said Tuesday.

In March, a bipartisan group of senators and House members introduced legislation to fund nearly $7 billion in national parks maintenance projects that have been on hold for years.

The maintenance backlog totals a daunting bill of roughly $11.6 billion in pending projects and upkeep.

The maintenance projects in the backlog include repaving roads and parking lots, renovating old lodges, and restoring bathroom facilities.

The National Parks Restoration Act represents a rare opportunity for lawmakers to address the maintenance backlog during President Donald Trump’s administration, which has sought to roll back funding for national parks and environmental protections in favor of increased opportunity for energy production and source exploration.

It is the only bill funding deferred maintenance projects that the president and his Office of Management and Budget have fully supported. They have swatted away similar bills over funding concerns.

The legislation in the House and Senate would divert a certain amount of revenue from energy leases and permits for federal land and offshore regions toward funding maintenance projects.

Interior Secretary Ryan Zinke said in March he had been discussing such a funding framework with lawmakers “to rebuild and revitalize our parks and communities” and touted the bill as “the largest investment in National Parks in our nation’s history.”

“It’s an old principal,” Alexander said Tuesday on a tour of the Chickamauga and Chattanooga National Military Park in Tennessee, the Chattanooga Times Free Press reported. “You use an environmental burden and turn it into an environmental benefit.”

Some interested parties have said the plan has its drawbacks, including a volatile funding stream that ebbs and flows based on energy prices and other factors.

“It relies on energy revenue being at a certain level,”Kristen Brengel, National Parks Conservation Association vice president of national affairs told the Times Free Press. “That fluctuates so much and isn’t guaranteed. It could be a lot of money, or it could be no money. It could make a lot of sense sometime in the future if we know oil and gas is going to be at a certain price above what it is now, but there’s no certainty in that.”

Neither the House nor the Senate has voted on the measure. It is not on the imminent agenda when lawmakers return to the Capitol next week.