Two Hanford workers have tested positive for radioactive waste in their bodies. It happened at the Plutonium Finishing Plant—a massive factory being demolished at the nuclear cleanup site in southeast Washington state.

The government and its contractors have been struggling to contain the spread of contamination at the demo site since June. But more and more contamination spread was found this winter since December.

The workers with contamination might have breathed in, or ingested radioactive waste. Officials say it’s at low levels. The person who tested positive with the highest levels, will get 10 millirem of dose over 50 years. That’s about the same as flying 10,000 miles in a commercial jet.

According to the Department of Energy that dose is above background levels, but “well below regulatory limits.”

As of now, 271 workers have requested bioassay tests and more worker test results are due back soon.