SPOKANE, Wash. (AP) — Two companies that do work at the Hanford Nuclear Reservation will pay fines of nearly $58 million for improperly billing the federal government for thousands of hours of work that were not performed.

Federal prosecutors announced the settlement involving the Hanford Nuclear Reservation, the nation’s most contaminated nuclear site.

The settlement was reached between Bechtel Corp. and AECOM Energy & Construction Inc., which for years have been constructing a giant nuclear waste treatment plant to clean up the Hanford site, which produced most of the plutonium for the nation’s nuclear arsenal.

The announcement was the second settlement agreement between federal regulators and the two companies.

The companies agreed to pay $125 million in November 2016 for allegations that they knowingly violated quality standards at Hanford and used substandard materials in constructing portions of the Waste Treatment Plant.