The studies were carried out by the Pacific Northwest National Laboratory on the behalf of the Department of Energy. According to the reports, waste from at least five of the tanks has seeped 70m below into local groundwater. Each tank contains approximately 204 million litres of radioactive material produced from plutonuim production in Richland, Washington.

Officials who spoke to 'The Oregonian' newspaper, which broke the story, believed Hanford's dry soil would soak up the pollution before it reached the aquifer. Handford contains 177 underground tanks, of which 67 are suspected of leaking.

There is a ongoing 29.5 billion dollar program to clean up the tanks to remove the radioactive solids. The report is unconclusive on whether the contamination in the groundwater would eventually seep into the Columbia River.

Hanford has pumped over 11 billion hectolitres of waste water into the ground since 1945, significantly contaminating the aquifer.