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SACRAMENTO — Federal and state environmental officials announced a settlement that could generate more than $800 million in new cleanup money for the Iron Mountain Mine Superfund site near Redding, home to what scientists say is the world’s worst water. 

The settlement with Aventis CropSciences USA Inc. – formerly known as Rhone Poulenc Inc. – will ensure that 95 percent of the highly acidic water coming from the defunct copper mine will be treated before it reaches the top of the Sacramento River system, said U.S. Environmental Protection Agency officials. 

The site is one of the nation’s most toxic Superfund sites. It is also home of the world’s most acidic water, according to scientists with the U.S. Geological Survey. 

“As recently as five years ago, this site dumped the equivalent of 150 tanker cars full of toxic metals into the Sacramento River each day during winter storms,” said Felicia Marcus, regional EPA administrator in San Francisco. 

Aventis, which is based in Stasbourg, France, has agreed to pay $160 million now for an insurance policy that will pay up to $300 million in cleanup costs over the next 30 years if it is needed, plus a final $514 million payment in 2030. 

In addition, the company has agreed to drop efforts to recover $150 million it already has spent on cleanup since 1989, said Tom Bloomfield, an EPA attorney. 

“When you add in the past costs they won’t seek to recover, the settlement approaches $1 billion,” Bloomfield said. It is the largest settlement in the EPA region that includes Arizona, California, Hawaii and Nevada, he said. 

With the agreement, the company is released from future liability, Bloomfield said. 

The Iron Mountain Mine, located about three hours north of Sacramento in an unpopulated area, was an active copper mine for more than 100 years and contains miles of tunnels, said Bloomfield. 

“If you took all the buildings south of Market Street in San Francisco, they would fit within the area that was mined out below Iron Mountain,” he said. “It was a big operation.” 

Those tunnels expose iron sulfate in the pyrite deposit below the mountain, which reacts with oxygen in the air and water to form sulfuric acid, scientists say. 

The neon green water that flows out of the mine’s portals has a pH level of 0.5 – the most acidic water found on the planet. Scientists say the closest previous measurements were found in volcanic lakes, but those were created naturally, while the mine’s water is the result of mining. 

Researchers from the University of Wisconsin and the Woods Hole Oceanographic Institute in Massachusetts discovered earlier this year that the mine is also host to a microbe that thrives in the highly acidic conditions. 

Scientists say the microbe speeds up the dissolution of iron in the water, compounding the pollution problems.