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Anadarko Petroleum agreed with the U.S. Justice Department to pay $5.15 billion to clean up 85 years worth of pollution left behind by its Kerr-McGee unit.

About $4.4 billion from the settlement — the government’s biggest-ever recovery for environmental cleanup costs — will be used to deal with contamination in thousands of sites across the country, including uranium mines in Navajo territories in the West, wood-treatment plants in Mississippi and Pennsylvania, and a chemical manufacturing site in Nevada that has led to pollution in Lake Mead.

The remaining money will be allocated to injury claims, according to court documents.

Shares of Texas-based Anadarko soared 15% Thursday on news of the settlement.

The pollution case stretches back nearly ten years. It was based on claims against Kerr-McGee, an Oklahoma energy and chemical company that Anadarko acquired in 2005 for $18 billion.

Kerr-McGee became infamous in the 1970s when Karen Silkwood, a labor activist, alleged the company was poisoning her with radioactive material at its nuclear materials plant outside Crescent, Oklahoma.

On Thursday, Anadarko’s market value rose to $50.7 billion based on its $99.02 close in New York.

The settlement didn’t cover any fines from the U.S. government that could be imposed for the 2010 Deepwater Horizon spill in the Gulf of Mexico.

Anadarko said it will record the impact of the settlement in its first quarter financial statements, including a $550 million net tax benefit.