A seven-room section carved out of the underground salt deposits near Carlsbad, New Mexico, has become the final resting place for transuranic waste. 

The leftover tools, rags, sludge and other materials contaminated with radioactive elements, filled the seven-room section, according to a KRQE report. Dubbed Panel 7, it’s part of the Waste Isolation Pilot Plant, the country’s only repository for such waste.

“Filling Panel 7 allows us to continue our important national mission of disposing of transuranic waste,” said Reinhard Knerr, the U.S. Department of Energy Environmental Management's Carlsbad field office manager, in a news release. Knerr said the program ensures the safety of those living near the waste.

Workers mined nearly 160,000 tons of salt to excavate the space, according to the Department of Energy (DOE). The space currently holds 20,056 containers of waste, including 13,000 55-gallon drums. A metal bulkhead sealed off the area. Over time, the surrounding salt will shift and settle, sealing in the waste.

The waste products come from the country’s nuclear defense program, which has been producing waste since the 1940s.  Panel 8 and two additional sections are scheduled for excavation and filling.