The Washington state Department of Ecology (WDE) on 29 April cited the US Department of Energy (DOE) as announcing that an underground radioactive and dangerous chemical waste storage tank at the Hanford Site in Southeast Washington was leaking. WDE’s Nuclear Waste Programme, along with the US Environmental Protection Agency, oversees DOE’s clean-up of Hanford.

“It’s a serious matter whenever a Hanford tank leaks its radioactive and dangerous chemical waste,” Ecology Director Laura Watson said. “Based on the information we have right now, the leak poses no immediate increased risk to workers or the public, but it adds to the ongoing environmental threat at Hanford.”

Tank B-109, which is at least 75 years old, is estimated to be leaking 3.5 gallons a day, or nearly 1,300 gallons a year. WDE has been concerned with this tank and tracking it for more than a year, when a formal leak assessment first began. B-109 is leaking into an area where other tanks have already leaked 200,000 gallons into the soil.

WDE said B-109 is 10 miles away from the Columbia River, and the water table is 210-240 feet below the tank. An estimated 1,700 gallons have leaked into the soil from B-109 dating back to March 2019.

The Hanford tanks contain widely varying volumes of mixed waste (waste with both radioactive components and dangerous chemicals), each with a unique blend of constituents. “This leak is adding to the estimated one million gallons of tank waste already in the soil across the Hanford site,” Watson said. “This highlights the critical need for resources to address Hanford’s ageing tanks, which will continue to fail and leak over time.”

WDE was notified about a year ago that DOE had started a formal leak assessment for B-109. At that time, DOE said the tank’s levels were decreasing but it was not sure why. WDE said it has been tracking the situation and was notified that DOE had determined that the tank is leaking.

WDE has authority under the Tri-Party Agreement, which governs the Hanford clean-up, to take immediate action in response to a leaking single-shell tank only if it is “necessary to abate an imminent and substantial endangerment to public health or welfare or the environment”. The state’s initial assessment is that, while any leak is a serious issue, there is no imminent danger. WDE said the next step is to try to reach agreement with DOE about the best path forward. It added: “If the two agencies cannot agree, WDE retains the authority to take an enforcement action and require specific actions to address the leak.”

The Hanford Nuclear Reservation was established during World War II and is the subject of a decades-long, multibillion-dollar clean-up effort. |It is the most contaminated site of radioactive waste in the USA. While operational, it produced about 66% of the plutonium used for US nuclear weapons, including the bomb dropped on Nagasaki, Japan, in 1945.

Tank B-109 is part of the 12-tank B Farm, which is one of Hanford’s oldest tank farms and is co-located with the BX and BY tank farms. B-109 has an estimated 15,000 gallons of liquid waste as part of its total waste volume of about 123,000 gallons. B-109 began receiving waste in 1946 and was taken out of service in 1976. It was still full of waste at that time, but no further waste was added. The tank was interim stabilised and declared sound in 1985. This tank received bismuth phosphate waste, evaporator slurry bottoms, Plutonium-Uranium Extraction Plant (PUREX) cladding waste, and B-Plant ion exchange waste.

An environmental impact statement from the National Environmental Policy Act said that "numerous geologic problems with the Hanford Reservation have been pointed out”. It added: “"Leaving the waste in the ground is just not acceptable. There is not enough information to take a chance on leaving any radioactive waste in the ground."

WDE communications manager Randy Bradbury told CBS News that it will take years to address the problem of the tanks. "They're all very well into the ground. "This isn't something that's going to happen next week or next month." He said WDE’s main concern is preventing the waste from reaching the Columbia River. "It will just basically sit around in the soil but in fact, it does migrate and some of it has migrated," he said.

“There is no increased health or safety risk to the Hanford workforce or the public,” said DOE spokesman Geoff Tyree. “Contamination in this area is not new and mitigation actions have been in place for decades to protect workers, the public and the environment.” DOE said the tank had been previously emptied of pumpable liquids, leaving a small amount of liquid waste inside, adding that systems in the area capture and remove contaminants that reach the groundwater and ensure the protection of the Columbia River.

However, an estimated 200,000 gallons of waste already has leaked from other tanks in the B-BX-BY tank farm complex, WDE said. This is the second of Hanford’s 149 single-shell tanks believed to be currently leaking waste, although in the past 67 tanks are suspected of leaking. The first leak was discovered in 2013, when DOE confirmed that Tank T-111 was leaking, it said liquid levels were decreasing at a rate of 150 to 300 gallons a year, or half a gallon to a gallon a day.

From the 1990s to about 2005, DOE removed as much pumpable liquid as possible from the single-shell tanks, leaving radioactive sludge and saltcake in the tanks to address concerns about leaks. “This is one we did empty out,” said Ben Harp, the deputy manager of the DOE Office of River Protection referring to Tank B-109. The 16 underground tanks that make up the B Tank Farm had 10 assumed leaker tanks previously. They are estimated to have leaked or spilled 157,000 gallons of liquid tank waste into the soil.

In addition, two adjoining Tank Farms, the BX and BY tank farms with a total of 24 single-shell tanks, are believed to have leaked or spilled about 200,000 gallons of waste in the past. However, the largest source of contamination comes from the historic practice of disposing of radioactive liquids in trenches and tile fields. At the B, BX and BY tank farms, an estimated 51 million gallons of contaminated liquids were poured directly into the ground.

With some contamination already reaching groundwater in central Hanford, DOE is pumping up contaminated water and cleaning it at the Hanford 200 West Pump and Treat plant. According to a detailed report in the Tri-City Herald, Hanford officials are concerned about the radioactive iodine and technetium in the leaking waste because it does not bind to the soil like other radioactive isotopes in the waste, making it move toward groundwater faster. Both are radioactive isotopes the 200 West Pump and Treat plant was designed to remove from groundwater.

DOE has some possible methods to address the leak and resulting soil contamination, Harp said. DOE has installed three ground-level plastic or asphalt barriers over areas of two tank farms to prevent rain and snow melt from carrying contamination already in the soil deeper toward groundwater. A barrier also could be installed over the B Tank Farm. There is a barrier installed over the T Tank Farm, which was constructed before the leak from Tank T-111 was detected. An exhauster also was installed in Tank T-111 to help evaporate tank liquids.

To date most of the waste from at least 17 of the site’s 149 single-shell tanks have been emptied into sturdier and newer double-shell tanks until the waste can be treated for disposal. Hanford has 27 double-shell tanks after a 28th tank was emptied and taken out of service when it sprang a leak between its shells, with the waste believed to be trapped between shells as the tank was designed to do.

DOE is working to start glassifying some of Hanford’s liquid tank waste at the $17 billion vitrification plant by the end of 2023.

Reports of the leak came a week after DOE announced the stabilisation of two underground structures at the Hanford site, which had been at risk of collapse. The partial collapse of a tunnel storing nuclear waste the nuclear reservation in 2017 had prompted a federal study which concluded in 2020 that a large settling tank and two trenches where plutonium-contaminated liquids were poured into the ground for disposal posed a high risk of collapse and contamination, Tri-City Herald reported. The largest of the three underground structures, which operated from 1955 to 1962, was estimated to be contaminated with 105 pounds (48 kilograms) of plutonium.

Scott Sax, president of Hanford contractor Central Plateau Cleanup Co, told employees that the three underground structures identified in the study were filled with concrete-like grout to prevent them from collapsing. He added that at least one of the trenches was buried deep enough to prevent nuclear waste from being released into the air in the event of a collapse. “Routine monitoring will continue to ensure all three structures remain stable,” Sax said, at least until further environmental clean-up action is taken. “With this work completed, Hanford has ensured the stability of these structures and reduced risks to workers and the environment,” said DOE’s Geoff Tyree.