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With all eyes focused on Butte's Superfund cleanup — including the Berkeley Pit, Silver Bow Creek, and the Parrot tailings — a waste site with the potential to impact human health has been left all but untouched eight miles west of town.

After nearly two decades of consideration, the Environmental Protection Agency is expected to announce sometime later this year a major decision on the Belgian-owned Solvay phosphorus plant's nearly empty site.

The closed plant is a half-mile south of Ramsay Elementary School in Butte's Tax Increment Financial District, a special economic zone for industry. The TFID, called Montana Connections, is home to the rail hub Port of Montana, FedEx, and REC Silicon. Montana's only twin-screen drive-in theater is immediately east of the site.

The closed plant is a 150-acre moonscape of radioactive slag dunes, evaporated tailings ponds, and skeletonized industrial structures visible from Interstates 15 and 90. But the site's most dangerous feature isn't so visible: a 500,000-gallon concrete tank filled with white phosphorus sludge. If the sludge ever touches the atmosphere, it will explode and release a toxic gas.

Currently the dangerous sludge is kept under control by a cap of 2 to 3 feet of water and, on top of that, rows of black plastic "bird balls" to keep migrating fowl from landing. Solvay project site manager Dan Bersanti said last month that if there is any water loss in the tank, an automatic system kicks in and replaces the lost water, so the tank always maintains the 2-to-3-foot water mark.

White phosphorus has the ability to quickly generate smoke that has made the material useful and common for a century among armed forces worldwide. It burns so hot — 5,000 degrees Fahrenheit — that its use as a munition against civilians was banned by the United Nations in the 1980s. White phosphorus burns victims to the bone. The tank holds the equivalent of 853,000 white phosphorus incendiary hand grenades.

Despite its dangers, phosphorous is used for a variety of household items, including baking soda, food preservatives, and agricultural fertilizer. The Butte plant processed phosphorous mostly to make laundry detergent up until the mid-1980s, Bersanti said last month.

But now with the plant and its operations long gone — operations came to a complete halt by 1997 — the question remains over what to do with the concrete tank and its contents. This question has occupied the EPA and plant owners for close to 20 years.

The plant has also occupied the EPA and the state in another way — through its storied past. A raid by federal and state investigators on the plant in 2000 resulted in a criminal trial in 2003. There have been two fires at the site. It is also, despite its hazardous waste, not a Superfund site but a Resource Conservation and Recovery Act (RCRA) site.

The site lacks a Montana-based EPA site manager. Federal oversight for the plant is coordinated directly from the EPA's Denver regional office. Butte and Anaconda's Superfund sites have Helena-based EPA site managers.

The EPA's decision later this year will be whether the federal agency OK's Solvay's recommendation to mine the sludge for profitable chemicals and potentially ship hazardous waste from other sites to Butte-Silver Bow for harvest, filling a "market niche," according to a 2015 study Solvay commissioned.

EPA Denver regional office public information officer Rich Mylott said through email that the EPA is considering "several alternatives."

The other options Solvay has come up with, listed in a 2015 supplemental waste plan, are capping the tank, which the EPA has historically opposed, or shipping its contents off to be incinerated, which Solvay has said is exorbitantly expensive and time consuming at $54 million over 20 years or more.

Could Butte become home to a new phosphorous recovery plant?

The phosphorus sludge in the tank is a byproduct of harvesting elemental phosphorus from phosphate ore. Typically the sludge was burned off for its remaining elemental phosphorus in a roaster, but when the plant was decommissioned in 1997, the clarifier wasn't emptied, Bersanti said in a 2001 letter, because it could no longer be done safely. So it has remained for nearly 20 years.

Solvay's desired solution to the tank and the dangerous muck within it would mean that Butte could become home to a facility that would mine the elemental phosphorus for resale. The new facility would be similar to the plant's old roaster. The roaster was torn down sometime after the plant closed in 1997.

The new facility, if built, could mine up to 98,000 gallons of elemental phosphorus recovered from the tank and sold for up to $2.5 million.

That does not include the waste from other parts of the country that would be shipped to Butte-Silver Bow for extraction.

Such a facility would take Solvay at least 10 years and cost $25 million to build.

BSB's TIFID administrator Kristen Rosa said the county supports Solvay's hope to build a phosphorous recovery plant.

"We are looking forward to them (Solvay) being able to move on and get the site cleaned up," Rosa said Friday.

Not only that, but BSB hopes to purchase a portion of Solvay's land — the site includes 900 acres, all within the TIFID district. Only about 150 are disturbed.

The portion that the county has its eye on is in the northeast corner of the Solvay property, close to the Port of Montana.

"It's a very separate parcel from everything they've developed on," Rosa said.

In addition, hundreds of acres to the west of the moonscape and black dunes where the operating plant once was also have not been disturbed. BSB has expressed interest in working with Solvay to develop that land as well.

Other options for the site

The other two options for the site are creating a permanent cap over the dangerous phosphorous or shipping it elsewhere for incineration.

After purchasing the site from Rhodia in 2011, Solvay compared the options in terms of long-term safety, reduction in toxicity, project safety, project length, and cost. While capping the clarifier is considered to be the short-term safest and cheapest option — $5.4 million over 2 years — capping would do nothing to reduce the volume of crude phosphorus, making it less safe long-term, the 2015 study states.

Safer than leaving the waste in place would be sending it off site to be destroyed, but Solvay projected this would cost ten times as much and take ten times as long as a cap. Bersanti said in mid-July that this is because the only facilities capable of incinerating the plant's crude phosphorus have never had to deal with so much at one time and can't burn it fast enough.

A 2015 Solvay study states that neither shipping the elemental phosphorous elsewhere nor building a new plant on site for phosphorous recovery would solve all the problems. If either plan is implemented, there would still be sludge left in the concrete tank, and Solvay would still have to have some sort of cap over what remained.

The 2015 study also states that both options have high risks for serious worker injury and medium risk for worker fatality for the duration of the sludge cleanup from both fire and phosphine gas.

Even so, Solvay's study recommends building a plant to extract and recover phosphorous from the sludge as the preferred cleanup method.

The EPA and Montana Department of Environmental Quality would have to sign off on commercial on-site extraction, and to store new hazardous waste on-site, Solvay would have to apply for the same kind of RCRA permit the site lacked and Rhodia was originally fined for in 2000 when the agencies initiated the raid.

The raid

Though many companies were responsible for the BSB site over the decades, Rhodia was left holding the hot potato when the EPA and MDEQ knocked on the gate with a search warrant in May of 2000. While plant owners didn't need special permission for the tank's sludge while the plant operated, as soon as the site shut down, the sludge legally became hazardous waste, which requires a RCRA permit to store. Rhodia didn't have one.

EPA and MDEQ investigators found the 2 feet of water capping the tank to be leaking, dropping the water level several inches. Bersanti said to investigators that the tank lost more water to evaporation. Just sampling the concrete tank's contents started fires that couldn't be extinguished with water until the phosphorus in the sludge samples burned up.

While the water cap keeps the white phosphorus from exploding, contact between the two releases toxic and flammable phosphine gas, which investigators detected during the raid to be at levels that exceeded legal workplace safety requirements.

South of the tank, investigators found furnace-lining bricks ranging in size from cinderblocks to refrigerators piled at the edge of the slag dunes. Leftovers from when the plant was scrapped, the bricks were caked thick with phosphorus. One brick ignited when an investigator tossed a rock at it; another brick burst into flames when an investigator flipped it over. The fire had to be smothered with sand for fear it would spread to the whole pile and spark a brush fire.

Investigators warned the company then that phosphate ore at the bottom of the plant's 119 acre kidney-shaped tailings pond could combust and release phosphine gas if the basin ever dried out. Satellite photos show it dried out in 2003. Bersanti said last month that the basin is now sprayed each summer with magnesium chloride, a common dust control compound, and has never caught fire.

After the 2000 raid, the EPA required Rhodia to concentrate the scattered furnace bricks within a newly erected fence before sending off the most contaminated for incineration.

The EPA ordered another new fence to be built around the tank. The EPA also required Rhodia to install a phosphine monitoring and capture system and to look into a long-term plan to deal with the tank's sludge.

The lawsuit

The EPA dropped the real hammer on Rhodia a week before Christmas in 2003, charging the French chemical company in U.S. federal court with two felony counts of illegally storing hazardous waste.

Rhodia pleaded guilty to both counts, and the company's assigned probation officer compiled a pre-sentence report — since sealed — to assist Judge Donald Molloy in determining the severity of Rhodia's punishment. The state found the report acceptable, but Rhodia objected to much of the report. Judge Molloy denied Rhodia's request to seal their objections, giving insight into the company's attempts to lessen their punishment.

In an objection filed to the court, company lawyers claimed Rhodia's probation officer had favored the EPA's factual narrative over the company's, leading to "a badly distorted picture of the situation at the Silver Bow Plant."

Rhodia lawyers accused the report of wrongly suggesting the company deceived MDEQ for years into believing there was no hazardous waste on the site, arguing instead that Rhodia believed at the time that the material was not hazardous and that Rhodia therefore could not have knowingly deceived MDEQ.

Despite the objections, Rhodia did not withdraw its guilty plea, and in 2004 Judge Molloy sentenced the company to pay $1.8 million to the MDEQ and $16.2 million in fines to the federal treasury, the second-largest penalty ever lodged under RCRA. Rhodia's plea deal required them to clean up the site.

Why no Superfund?

RCRA exists to manage hazardous waste on sites still operating, while Superfund is typically for the cleanup of abandoned waste or sites no longer operating. The BSB site was still producing elemental phosphorus during the EPA's Superfund consideration, but the plant shut down within five years after the EPA chose not to declare it a Superfund spot in 1992.

According to Superfund decision documents, the EPA knew there was hazardous waste on site but couldn't determine if documented pollution in the area was from the phosphorus plant or the area's numerous other Superfund sites in Butte and Anaconda. The EPA also considered Ramsay's population too small for concern of exposure to hazardous chemicals. The EPA did not include the concrete tank in its investigation.

Solvay now owns the site, but the place has changed hands and nationalities a half-dozen times. Originally built by the Victor Chemical Company in the early 1950s, Stauffer owned the plant almost from its inception until the company was swallowed by a series of bigger and bigger fish as the international chemical industry consolidated. Between 1985 and 1998, the BSB site was owned by Stauffer, Chesebrough-Pond Inc., Unilever, Imperial Chemicals, Rhone-Poulenc, and then Rhodia.

The rocket explosion

With the help of the Montana Aerospace Development Association and the county's blessing, Rhodia got the green light in 2009 to rent out portions of the phosphorus plant for the testing of experimental hybrid fuel rockets.

Silicon Valley-based Space Propulsion Group tested rockets in a structure paid for by the county on top of the phosphorus plant's old rail car dumping pit 550 feet due east of the tank over open ground. By January 2011, SPG had successfully tested dozens of rocket motors using liquid oxygen to ignite paraffin candle wax and was preparing to test their largest rocket to date.

The rocket exploded immediately after ignition, destroying the test building and scattering debris over half a mile across the plant. The exact cause of the explosion is classified by the Joint Army Navy NASA Air Force Interagency Propulsion Committee. SPG chief engineer Brian Evans and MADA president David Micheletti blamed the explosion on the liquid oxygen freezing a gasket, leaking from a closed valve, and pooling in the test chamber. SPG and MADA's insurance didn't cover the building's destruction, costing the county $168,000.

Rocket testing resumed five months later, with no accidents since in hundreds of motors. SPG still uses the railcar dumper pit but also a new site 300 feet southwest of the concrete tank. Blast mats of woven elevator cable replaced dedicated test structures to deflect shrapnel from an explosion, and Evans said SPG's new rockets are brittle flyweights that fail before dangerously explosive pressure can build up.

"We learned so much from that incident," Evans said.

It wasn't the plant's first accident since decommissioning. In August of 2001, a small storage tank previously unknown to the EPA started a fire when a hole rusted through and allowed the phosphorus within to spill and make contact with air. The fire was noticed by Bersanti's wife from the freeway, according to The Montana Standard in 2001. Bersanti and a contractor smothered the fire with slag.

What happens after the EPA's decision on the tank?

Even after the EPA's decision on the concrete tank is handed down, the EPA will still have other decisions to consider about the site — namely, what to do about the 10 million tons of slag dunes. There is also the 75-to-80-acre tailings basin, which sits west of the concrete tank, and scrap metal sitting out on the site that emits low levels of radiation.

Mylott says the public has nothing to worry about and that the EPA is working toward a solution to the former plant's disturbed property.

"While immediate exposure risks have been addressed at the site, the over-arching goal of the (EPA) 2004 order (to Rhodia and now Solvay) is to hold the facility owners accountable for a deliberate and thorough site investigation and the implementation of effective, long-term cleanup remedies," Mylott said via email.

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Nat'l Resources / General Reporter

Environmental and natural resources reporter for the Montana Standard.

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