A leak in the basement of Honolulu’s Daniel K. Inouye International Airport may be a pricey problem to fix.

The state Department of Transportation recently approved a contract with engineering company Oceanit Laboratories Inc. for $500,000 to locate the source of the water leaking into the basement of the overseas terminal and international arrivals building, and figure out a way to stop it.

The contract does not include the task of actually fixing the leak, which will cost extra, said Tim Sakahara, spokesman for the department.

The basement of the airport has been leaking for years — probably more than 10 years — but the water has not interfered with airport operations, Sakahara said.

Still, the water seeping in from the floor has defied all attempts at a fix by airport staff, and state officials installed a sump pump to remove water as needed and deposit it into a drainage area, he said. Sakahara could not estimate how much water is involved, saying the leak is not consistent.

The basement was built in 1973 and is below sea level, and a liner was installed to try to keep water out. That liner might have deteriorated, which may be causing the leak in the room adjoining a baggage-handling area in the 360,000-square-foot basement, Sakahara said.

“It is kind of an intricate process that they’re going to have to go in and try to figure it out and make the fixes,” Sakahara said. “The difficulty has been trying to determine the exact source of the leak … without tearing up the floor.”

The leak is in a side room that houses huge fans that circulate air into the basement for ventilation, he said. There has been no damage apart from some cracking of the concrete floor, he said. The leak is “not major by any means, and it’s not in a high-traffic area,” he said.

Sakahara said the problem is not believed to be associated with sea level rise.