Federal lands would become a bigger source of revenue that helps maintain the infrastructure of national parks under a proposal supported this week by Colorado U.S. Rep. Scott Tipton.

Tipton, R-Cortez, asked expert witnesses during a congressional hearing about the possibility of using leases and fees on energy companies to clear away an $11.6 billion maintenance backlog in national parks.

The leases and fees have generated an average of $9 billion a year for the past 20 years, mostly from rights granted to companies for oil and gas drilling, according to National Parks Service figures.

Tipton asked whether rights to generate energy from renewable power on federal property could be another way of “trying to get a sustainable revenue source” for maintaining national parks’ roads, buildings and other infrastructure. Renewable energy normally refers to electrical generation from solar panels, wind generators and geothermal plants.

For years Tipton has advocated what he calls an “all of the above” approach to power generation. It refers to maximizing the efficiency of a variety of energy sources like oil, natural gas, coal, solar panels, wind generators and geothermal.

He mentioned that the U.S. Interior Department collected $18 billion a year from energy companies in 2008. Under the Obama administration’s stricter environmental policies, the figure dropped as low as $2 billion.

P. Daniel Smith, the National Parks Service’s deputy director, agreed that federal lands could be used to grant more leases for renewable energy, thereby increasing government revenue.

He testified during a hearing of the House Natural Resources subcommittee on federal lands.

Smith emphasized the urgency for Congress to resolve the lack of good repair in national parks.

“The network of roads, trails, restrooms, water treatment systems, drinking water and visitor centers are aging and are exceeding a capacity they were often never designed to hold and support,” Smith said.

The subcommittee is trying to decide between two bills to fund a restoration of national parks.

One of them is the National Park Service Legacy Act, which would dedicate specific amounts of tax revenue for park maintenance for the next 30 years. It would start with $50 million in its first year and gradually increase to $500 million a year from fiscal 2027 through 2047.

The Trump administration and most Republicans support a second bill, called the National Park Restoration Act. It would contribute as much as $18 billion over 10 years to a park maintenance fund.

“Without a dedicated funding source, the deferred maintenance backlog will continue to grow,” Smith said in support of the National Park Restoration Act. “The backlog of projects at our National Parks limit access, impair visitor experiences and impact recreational opportunities.”

Although the amount of money could be greater under the National Park Restoration Act, it also creates the most controversy. The money would come largely from leasing federal lands to corporations that extract oil, gas or minerals from them.

Environmental advocacy organizations, such as Conservation Colorado, have expressed deep concerns about the National Park Restoration Act.

“Selling off our public lands and resources to the highest bidder to cover the costs of maintaining them isn’t an answer,” Scott Braden, public lands and wilderness advocate for Conservation Colorado, said in a statement to Colorado Politics. “It simply doesn’t make sense to promote harmful practices like drilling or mining on public lands as a way to pay for their upkeep. We cannot save one place by destroying another. National parks belong to all Americans, not just the industries that want to profit off them.”

Nearly 24 million acres, or 36 percent of the Colorado’s land, is owned by the federal government.

National parks in the state include Black Canyon of the Gunnison National Park near Montrose, Great Sand Dunes National Park and Preserve near Mosca, Mesa Verde National Park near Cortez and Rocky Mountain National Park near Estes Park and Grand Lake.

The National Park Service estimated it completed more than $650 million in maintenance and repair last year nationwide. However, the work only barely kept pace with the rate of deterioration.

The infrastructure includes more than 5,500 miles of paved roads, about 1,700 bridges and tunnels, an estimated 24,000 buildings and 1,000 miles of pipelines.

Yellowstone National Park officials say they need road repairs. At New York’s Ellis Island, the seawall is crumbling. At Arlington National Cemetery, buses and heavy trucks are banned from a bridge that connects the cemetery with the Lincoln Memorial. At the Grand Canyon, the water pipeline system is breaking down.

Interior Secretary Ryan Zinke overlooked the controversy over leasing federal land when he issued a statement supporting the National Park Restoration Act this month.

“Infrastructure is an investment, not merely an expense,” Zinke said. “And every dollar we put into rebuilding our parks, will help bolster the gateway communities that rely on park visitation for economic vitality.”