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The chemical company Solvay should build a facility west of Butte to harvest phosphorus from waste left behind when the plant closed in 1997, the Environmental Protection Agency has decided.

EPA chose the $25 million, 10-year “mud-still” harvester option over two other proposals by Solvay to cap the waste on-site or take it off-site to be incinerated.

The mud-still is Solvay’s preferred option, according to a 2015 waste plan exploring options for cleaning up 500,000 gallons of flammable phosphorus sludge in the plant’s old clarifier tank. The sludge will ignite if it touches air.

To pay for the plant, Solvay has suggested it could use the plant for commercial purposes, importing waste to process after the cleanup is done. But that would require signficant permitting at both state and federal levels, after a cleanup expected to take a decade.

The 150-acre phosphorus plant is a half-mile south of Ramsay School, across Silver Bow Creek, and produced elemental phosphorus from phosphorus ore from 1952 to 1995 before shuttering. A raid by state and federal regulators in 2000 found the clarifier tank sludge and other hazardous waste improperly stored, and then-plant owner Rhodia Inc. was fined $16.2 million in federal court in 2004.

Solvay bought Rhodia in 2011, inheriting a requirement under the Resource Conservation and Recovery Act — similar to Superfund — to clean up the site. Fencing off hazardous waste and cleaning up portions of the site happened early on, but the flammable clarifier tank sludge has sat for 20 years.

EPA has been deciding how to clean up the phosphorus sludge since 2002, when the agency denied Rhodia Inc.’s recommendation to merely cap the waste on-site. The Montana Standard reported then that EPA’s Montana office director John Wardell told plant manager Dan Bersanti in a letter that “EPA will not agree to capping in place unless there are no other options.”

An EPA order in 2003 sent Rhodia back to the drawing board. Twelve years later Solvay came back with the same options proposed, but this time recommended on-site treatment with a mud-still instead of just capping.

One reason Solvay personnel said in the waste plan that they prefer on-site remediation is that shipping the sludge off to be destroyed would be too expensive and take too long — $54 million over 20 plus years — because no incinerator has ever had to deal with so much at once.

The waste plan said Solvay’s mud-still could “fill this market niche” for large scale incineration if the EPA and the Montana Department of Environmental Quality allowed the company to import phosphorus-containing waste from other facilities for harvest.

Solvay expects to extract $2.5 million worth of commercial-grade elemental phosphorus from the clarifier tank alone. But that won't pay for the construction of the $25 million plant.

Kristie Ponozzo, DEQ public policy director, said Solvay won’t be making money off shipped in waste any time soon. Ponozzo said the EPA decision does not greenlight Solvay to import waste, and that cleanup must be completed before the mud-still could be used for commercial purposes. Commercial activity would also require extensive environmental permitting, and be separate from clean-up activities, Ponozzo said.

But Solvay's first responsibility, and the sole subject of EPA’s proposed corrective action decision and public comment period, is the cleanup of the clarifier sludge, said EPA spokesman Richard Mylott.

"If Solvay proposed to treat offsite waste following the completion of any remedy for the clarifier sludge, they would be required to apply for a RCRA permit from Montana DEQ," he said.

Solvay issued this statement in response to EPA’s most recent decision:

"After considering environmental and technical aspects of several options, EPA’s recommendation marks a milestone toward ensuring the safe disposal of the on-site phosphorus.

“Further steps are required before EPA’s recommendation can be implemented. Solvay has not received any regulatory approval for treating phosphorus from any other source," the statement read.

Solvay has successfully tested a prototype mud-still, but still needs to design, permit, build and test the full-size facility, which the company projects will take at least two years. The waste plan states the facility would operate for at least five years, with total time from start to finish approximately 10 years given its experimental nature. The plan would end with a cap built over the clarifier tank.

According to conceptual layouts, the mud-still requires a 4,300-square-foot facility be built between the clarifier tank and a “blast mat” where Silicon Valley-based Space Propulsion Group tests experimental rocket motors, one of which exploded in 2011. SPG did not respond to questions as to how the EPA’s decision will affect rocket testing at the phosphorus plant.

When the plant was operational, clarifier sludge was incinerated in a roaster on-site for its remaining elemental phosphorus. Plant manager Bersanti said in a 2001 letter that the feed system from the tank to the roaster became unsafe to operate in May of 1997, and the remaining sludge was left to sit in the clarifier. The roaster was torn down along with most of the plant.

EPA’s decision does not address the numerous other sources of waste at the Silver Bow phosphorus site, including 10 million tons of radioactive slag, and a dried tailings basin DEQ has warned in the past could ignite.

Tuesday’s legal notice comes ahead of any formal press release by EPA, and is the agency’s first announcement of the decision.

“We weren’t notified,” Butte-Silver Bow Chief Executive Matt Vincent said, “but progress is good.”

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