Sometimes, the heating and air-conditioning system at the Hopewell Culture National Historical Park Visitors Center goes on the fritz.

Sometimes, the heating and air-conditioning system at the Hopewell Culture National Historical Park Visitors Center goes on the fritz.

Because he is in charge of the 2,000-year-old artifacts inside that building -- things including copper carvings that are particularly sensitive to temperature change -- such a system failure gives park superintendent Dean Alexander a headache that he doesn't need.

But when he considers that he is one cog in the wheel of a national-parks system that faces nearly $12 billion in long-delayed maintenance projects, Alexander said he realizes that Hopewell's less than $500,000 in deferred projects make him luckier than most.

And besides, as the National Park Service celebrated its 100th birthday Aug. 25, Alexander would rather focus on the positive: a new trail and overlook that will open to the public at the Hopewell Earthworks, one of six archaeological sites that make up the Chillicothe park in Ross County.

"The National Park System has a lot to celebrate," said Alexander, who also oversees the Dayton Aviation Heritage National Historical Park. "Yet the public should be made aware of our needs."

And that's exactly what parks-service officials hope -- that this centennial celebration will increase appreciation of the system, lead to greater public support and translate to more public and private investment to sustain it.

Despite the backlog in maintenance projects, the National Park Service is on pace for its third consecutive record year of attendance, said spokesman Jeffrey Olson. The system saw 292.8 million visitors in 2014, 307.2 million in 2015 and those figures are expected that to increase by at least 3 percent this year.

And on Aug. 24, the 87,000-acre Katahdin Woods and Waters National Monument in Maine became the system's 413th park.

The parks service announced in February that its list of deferred maintenance projects -- defined as necessary work on roads, bridges, trails, campgrounds, buildings and physical plants put off for at least a year -- grew by $440 million from the year before.

President Barack Obama has twice proposed mandatory funding to get rid of the list within five years, but nothing has come of his proposals.

"We have to be able to stop the growth of that deferred maintenance list, and we are not yet at that point," Olson said.

The parks service's total budget appropriation from Congress this year was $2.85 billion.

Some of the pressing maintenance issues at national parks have been well documented: Alcatraz in California is crumbling; Mammoth Cave in Kentucky has dirt trails that are growing dangerous; Glacier National Park in Montana needs a new fire-suppression system.

Closer to home, Ohio's eight parks have their own problems. Cuyahoga Valley National Park, for example, has delayed maintenance needs totaling almost $41 million.

Chris Powell, spokeswoman for the Midwest region of the parks service, which includes Ohio, provided a list of some of the priority deferred-maintenance projects in Ohio. Big-ticket items at Cuyahoga Valley include fixing and replacing bridges and demolishing five old structures.

Other big projects on the waiting list in Ohio include a nearly $5 million renovation of a historic house at the Charles Young Buffalo Soldier National Monument at Wilberforce, and nearly $2.5 million in work at Perry's Victory and International Peace Memorial at Put-in-Bay.

The parks service has created a number of programs in recent years that aim to turn young people into faithful supporters, and this centennial can only help spread the message, Olsen said.

"There's been this rolling interest, this voice, this chorus, coming from the next generation of park users and supporters," he said. "But the park system doesn't stand still, and it's not inexpensive to care for."

The national parks that charge fees are waiving them through Sunday. For more information on parks and the centennial, visit