YAKIMA, Wash. – Six underground tanks that hold a brew of radioactive and toxic waste at the nation's most contaminated nuclear site are leaking, federal and state officials said Friday.

Washington Gov. Jay Inslee said the leaking material poses no immediate risk to public safety or the environment because it would take a while – perhaps years – to reach groundwater.

But the leaking tanks raise new concerns about delays for emptying them and strike another blow to federal efforts to clean up south-central Washington's Hanford nuclear reservation, where successes often are overshadowed by delays, budget overruns and technological challenges.