YAKIMA, Wash. (AP) - Washington state fined the U.S. Department of Energy $500,000 on Tuesday for a radioactive hazardous waste spill at the nation's most contaminated nuclear site.

The spill occurred July 27, when workers at south-central Washington's Hanford nuclear reservation were pumping waste from an underground tank. When a pump blocked, they tried to unblock it by running it in reverse, but 85 gallons of waste spilled onto the ground.

"Before the spill was discovered, a series of poor decisions put workers in grave danger from exposure to the tank waste and vapors," Jane Hedges, manager of the state Department of Ecology's Nuclear Waste Program, said in a statement. "This accident calls into question the adequacy of the safety culture which is so critical at the tank farms."

The Energy Department developed more than 200 corrective actions after the incident and has been monitoring and reviewing tank farm operations in the months since, spokesman Erik Olds said.

"Removing waste from aging single-shell tanks is one of the department's highest priorities at Hanford, and we remain committed to the highest standards for the safe, effective and environmentally safe completion of this work," he said in a statement.

Sixty-three workers were within 200 meters, or 656 feet, of the spill and were identified for ongoing medical monitoring. Of them, 13 workers have complained of symptoms that could be attributed to the spill, including upper respiratory problems, upset stomachs, headaches, dizziness, eye irritation and blurred vision, Olds said.

The Energy Department will continue to work with all of those affected employees to ensure continued medical evaluations and health care, he said.

Olds said it was too soon to say whether the Energy Department would appeal the fine.

The federal government created Hanford in the 1940s as part of the top-secret Manhattan Project to build the atomic bomb. Today, it is the nation's most contaminated nuclear site with cleanup expected to continue for decades.

Much of the cleanup involves treating 53 million gallons of highly radioactive waste that has been stewing in 177 aging underground tanks. Most critical is the waste in 149 tanks that have a single-wall construction, making them more susceptible to leaks as they age.

The single-shell tanks, built from the 1940s through the '60s, were designed to last about 20 years. An estimated 67 of them have leaked about 1 million gallons of radioactive brew into the soil, contaminating the aquifer and threatening the nearby Columbia River.

So far, seven single-shell tanks have been emptied to meet regulatory requirements. Contractor CH2M Hill Hanford Group is handling the tank waste cleanup.

The state Department of Ecology issued the fine under the Tri-Party Agreement, a cleanup agreement signed by the state, Energy Department and the U.S. Environmental Protection Agency.

The fine cited two violations: for an inadequate design of the waste retrieval system, and for inadequate engineering reviews required by state regulations.

Hedges also said she was troubled by the length of time it took the contractor and the Energy Department to determine there was a spill.

"There was a delay of more than seven hours from the time the first high radiation readings were discovered," Hedges said in the statement. "This is completely unacceptable."

Last month, the Energy Department notified CH2M Hill that it would see a $500,000 cut in payments as a penalty for the spill. However, the contractor could earn back half that amount by completing all of the corrective actions that were identified in an investigation into the incident.

Meanwhile, none of the highly toxic, radioactive sludge is being emptied from other leak-prone, single-shell tanks until the contractor is sure problems will not recur.

Last month the Energy Department reached an agreement with its regulators to settle a $1.14 million fine for cleanup failures at Hanford. That penalty concerned operations at a landfill for contaminated soils and other hazardous and radioactive waste.

It was the largest fine levied by the Environmental Protection Agency's Northwest office for Hanford work.