A tank containing highly radioactive waste may be leaking into the soil at the Hanford Nuclear Reservation (the US’s most contaminated nuclear site) in Washington state, employees have told media.

State and federal officials are investigating reports that workers detected elevated radioactivity levels under tank AY-102 during a routine inspection on Thursday.

According to technician Mike Geffre, who works for contractor Washington River Protection Solutions, an inspection was made of a pit under the tank. Its water samples had an 800,000-count of radioactivity and a high dose rate, which means that workers must reduce time spent in the area.

"Anything above a 500 count is considered contaminated and would have to be disposed of as nuclear waste," Geffre explained. "Plus, the amount of material we've seen from the leak is very small, which means it's a very strong radioactive isotope."

If the waste escapes the tank and gets into the soil, it may reach groundwater and potentially the Columbia River.

"This is really, really bad. They are going to pollute the ground and the groundwater with some of the nastiest stuff, and they don't have a solution for it," Tom Carpenter, executive director of the Seattle-based advocacy group Hanford Challenge, a watchdog group that conducts environmental sampling to monitor for radioactive and chemical contamination, told AP.

A sign is seen as you enter the world's largest environmental cleanup project at the Hanford Nuclear Reservation 30 June, 2005 near Richland, Washington. (Jeff T. Green/Getty Images/AFP)

There are 177 tanks holding up to 56 million gallons of waste, 149 of which are single-shell. Six of those tanks were discovered in February to be leaking at a rate of about 1,000 gallons annually.

AY-102 is one of Hanford's 28 tanks with two walls, which was installed when single-shell tanks began leaking and some of the most radioactive liquid in those tanks was pumped into the sturdier double-shell tanks. The tanks are now beyond their intended life span.

Two radionuclides comprise much of the radioactivity in Hanford's tanks: cesium-137 and strontium-90. While both take hundreds of years to decay, exposure to either can increase the risk of cancer.

Officials say that leaking tanks pose no immediate threat to the environment or public health, with the closest communities being several miles away.

"These last few months just seem like one body blow after another," said Ken Niles of Oregon's Energy Department. "It's true this is not an immediate risk, but it's one more thing to deal with among many at Hanford."

“The Energy Department has been actively monitoring double-shell tank AY-102 since it was discovered to have a slow leak from the primary tank,” the department said in a statement. “Workers detected an increased level of contamination during a routine removal of water and survey of the leak detection pit.”

Additional testing is expected to take several days, though the state will demand an accelerated plan to deal with all the waste at Hanford, said Washington Governor Jay Inslee, adding that the potential leak "raises very troubling questions."

55-gallon drums containing transuranic (TRU) waste are prepared for shipment at the Waste Receiving and Processing facility (WARP) on the Hanford Nuclear Reservation, 30 June, 2005 near Richland, Washington. (Jeff T. Green/Getty Images/AFP)

An engineering analysis team will conduct additional sampling and video inspection to determine the source of the contamination, Spokeswoman Lori Gamache said.

The Energy Department announced last year that AY-102 was leaking between its two walls, but gave reassurances then that no waste had escaped. However, Seattle’s KING5 television station has reported that the cleanup contractor and the department knew a year earlier that the tank was leaking.

At the height of World War II, the federal government created Hanford as part of a secret project to create the atomic bomb. The site ultimately produced plutonium for the world's first atomic blast and for one of the two atomic bombs dropped on Japan; it continued production through the Cold War.

These days, it has a reputation as the nation's most contaminated nuclear site, with a cleanup expected to take several decades. It costs up to US$2 billion annually and has already set taxpayers back US$40 billion, with US$115 billion more expected to be needed.

The biggest challenge thus far has been removing highly radioactive waste from the 177 aging underground tanks and constructing a plant to treat that waste, which will be encased in glasslike logs for permanent disposal. Workers designing and building the unique plant have encountered numerous technical problems, however, as well as delays and rising costs. The plant is unlikely to begin operating before 2019, far beyond the original 2011 deadline.

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