BOISE, Idaho (AP) — Fines paid by the U.S. Department of Energy to Idaho for missing a deadline to get radioactive liquid waste out of underground storage tanks have surpassed $3.5 million and the money could be used for enhanced monitoring of a huge aquifer beneath the site, officials say.

The federal agency started paying the fines in 2015 for violating a 1992 agreement involving 900,000 gallons of waste sitting above the Eastern Snake Plain Aquifer at the department's isolated desert site in eastern Idaho that includes Idaho National Laboratory, the nation's top federal nuclear research lab.

Officials say contamination from the 890-square-mile (2,305-square-kilometer) site reached the aquifer through injection wells, unlined pits and accidental spills, mainly during the Cold War era before regulations to protect the environment were put in place.

The U.S. Geological Survey last year released a report saying monitoring of existing wells found the aquifer to be as free of radioactive contamination and other pollutants as it has been in more than six decades of monitoring.

Federal and state officials are currently discussing spending about $2.2 million of the money generated by fines for monitoring wells in the aquifer that's used by cities for drinking water and farmers for irrigation.

"Anytime we can enhance the protection of the Eastern Snake Plain Aquifer, that's a benefit to Idaho," said Natalie Creed, manager of the Hazardous Waste Unit at the Idaho Department of Environmental Quality.

The Energy Department has paid some of the fines in cash that goes into an account used to respond to emergency hazardous waste situations anywhere in the state.

The rest of the money is used for environmental projects.

The federal agency has until the end of May to formally propose the aquifer monitoring project, and state and federal officials have been communicating about it. Creed said she has asked the federal agency for more information about how the monitoring project might benefit the environment.

Roy Bartholomay, chief of the U.S. Geological Survey's Idaho National Laboratory Project, said the proposed additional monitoring of wells could help that agency's tracking of radioactive material in the aquifer.

Some of the possible new wells and other monitoring equipment would be in the Lost River Basin, an area where the Lost River disappears into the ground and is not well understood. Part of the river, when it's flowing, reaches the Energy Department site.

"At this stage, there's a need for a lot more data to make that a better flow model," Bartholomay said.

The Idaho Water Resource Board has already approved spending the $2.2 million — if it gets it — for the wells and monitoring. The agency's primary objective is to get a better understanding of the surface and underground water flow to allocate water to irrigators.

"There are a lot of water-use conflicts in the Big Lost," said Brian Patton, manager of the state's Water Planning Bureau. "We want to get a better handle on the hydrology of that system so we can make better management decisions."

The daily fine of $6,000 levied on the Energy Department will continue while radioactive waste remains in the tanks. The Energy Department built a $600 million facility to treat the liquid waste, but it has failed to work.

The Energy Department didn't respond to inquiries about the situation.

The failure to remove the liquid waste has also left the Energy Department in violation of a separate, 1995 agreement preventing experimental quantities of spent nuclear fuel from entering the state for examination at Idaho National Laboratory.

Idaho for a number of years granted extensions to the Energy Department before finally initiating the fines in 2015.

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