The rose bush in Shirley Melancon’s front yard used to bloom full and pink, but recently she noticed the flowers from the 100-year old plant are coming in white and shriveled.

She doesn’t know why this is, but it’s difficult not to wonder if there’s a link to the sprawling radioactive waste storage structure that sits less than a mile from her tidy cottage in the fourth district of St James Parish, Louisiana.

It is a gargantuan manmade 960-acre lake containing hundreds of millions of gallons of toxic, radioactive water that sits on top of a 200ft pile of waste byproduct, an enormous, chalky white wall that makes the bulldozers and cranes atop look like children’s toys. The massive white mound is shaped like a giant bathtub, formed with a naturally radioactive element called phosphogypsum and filled with toxic cargo. It has reshaped the horizon in this parish, which has transitioned from a center of slavery, to black-owned farmland, to an industrial corridor.

Melancon lives close enough to the big “gypstack” mound as it’s known, to hear occasional sirens and loudspeaker announcements. “If that broke open, how could you contain it all?” wondered Melancon from her front patio.

And fears of exactly this scenario of a breach grew dramatically in January, when it emerged one of its walls was found to be shifting by as much as 0.7in a day, potentially threatening to spill its store of 750m gallons of toxic, radioactive wastewater on to surrounding lands and waterways.

Facebook Twitter Pinterest The Mosaic pile. Photograph: Phin Percy

‘They don’t tell us anything’

The 87-year-old lives in the heart of an area known as Cancer Alley, a stretch of land between New Orleans and Baton Rouge along the Mississippi River with a dense concentration of petrochemical and industrial plants, and some of the nation’s highest cancer rates. Her municipality neighbours Saint John the Baptist parish, which is the focus of a year-long Guardian series, Cancer Town, examining the fight for clean air in an area that has the highest risk of cancer due to airborne toxins, according to US government science.

Melancon is affiliated with a group of activists, led by black women, many of whom can trace their ancestry to former slaves from nearby plantations, fighting on multiple fronts to stop further industrial development in this already heavily polluted and economically disadvantaged area.

But that giant lake of industrial waste, and the piles of phosphogypsum containing it, is the most concerning to Melancon right now. It is owned by the Mosaic Company, a fertilizer producer, and lies directly across from her front porch.

Even as the Louisiana department of environmental quality (LDEQ) considered the discovery of the shifting wall in January an “emergency condition” and Mosaic told some farmers that it leases land to that they could not be on the property for months, residents only heard about the situation after it was reported in the local news.

“None of us knew what was up,” said Matthew Jacques, 28, said of the situation. He lives in a house two doors down from Melancon. “They don’t tell us anything.”

For many residents in this predominantly black area, LDEQ and the companies behind pollutive industries have a virtually non-existent approach to community health and safety. “We feel that it’s environmental racism, because basically where most of the plants are located is where black people are staying,” said Barbara Washington, a lifelong resident of the area and a member of Rise St James, the environmental justice group formed by parish residents. “They just let us die out here,” said Washington about the experience of living in Cancer Alley.

The Mosaic fertilizer plant has been a continuing source of concern among many residents since opening in the 1970s. Even at the best of times, the storage site across from Melancon’s house, known as the Uncle Sam site, is an eyesore that has been under a consent decree since 2015 for releasing excessive amounts of sulfur dioxide and sulfuric acid mist into the air.

A farmer who grows sugarcane on Mosaic property adjacent to the gypstack was the first to alert the company to the problem last December, when he reported a land bulge – about 2,000ft long and 100ft wide – that was pushing on the north wall of the gypstack, causing it to move.

Since the shifting wall was first reported to state authorities on 10 January, the company has been scrambling to reduce the imminent threat of a gypsum break.

“If there’s any kind of spill, we’re looking at a world-class environmental disaster,” said Darryl Malek-Wiley, a senior organizing representative with the Sierra Club who has been tracking the Mosaic plant since the 1980s, when it unsuccessfully lobbied the EPA for permission to dump all gypsum waste into the Mississippi River. “I do not feel they have it anywhere close to under control.”

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The gypstack pile is made of phosphogypsum, which is a byproduct of the process that converts phosphate rock into a type of fertilizer widely used on large farms. For every ton of phosphate fertilizer, about 5.5 tons of phosphogypsum waste is created, which then must be kept indefinitely in stacks, or gypstacks, because it is weakly radioactive.

Mosaic argues the dangers of this massive gypstack are overstated. Spokeswoman Callie Neslund said the company has drastically reduced water levels in the giant tank, and has also undertaken efforts to counterbalance movement of the shifting wall with the construction of a large earthen ramp. The company says that the gypstack itself may no longer be moving due to data readings on the gypstack remaining within the “margin of error” and farmers leasing land have been allowed back on the property.

State regulators could not confirm movement had stopped.

Residents and activists say the danger from Mosaic is far from over. A company decision to idle its Louisiana plant until the end of the year, leaving a skeleton crew of 65-80 employees, has raised concerns among many here and prompted some still unanswered questions from regulators on how the company will handle on-site wastewater during the shutdown.

In late October, Mosaic told the LDEQ that heavy rainfall had prompted the company to begin emergency water diversions from its gypstack system to other storage areas on site. Over the past month, the total amount of wastewater stored on the Mosaic site increased by over 100m gallons. Water levels within the gypstack that had found to be shifting in January remained slightly above 180ft on 31 October, 1ft above EPA recommended limits.

Fans plan prompts new fight

Residents are also concerned about Mosaic’s pursuit of a plan to further cut water levels by installing huge fans on the top of the gypstack that would spray a fine mist of untreated, contaminated wastewater into the surrounding area.

The firm defends the plan to use four giant fans known as “spray evaporators” and says the contaminated mist will not travel, roughly, beyond the storage pond perimeter.

Residents are skeptical. “How can they possibly get away with that, knowing there’s people in the area?” asked Myrtle Felton, a member of Rise who lives about a half-mile from the Uncle Sam site. “They don’t care,” said Gail Lebouef, another Rise member who lives nearby.

Malek-Wiley, who questions the accuracy of Mosaic’s model predicting mist dispersion, called it “one of the craziest ideas I’ve ever seen”. He said of particular concern is the hydrogen fluoride in the water, a potent chemical that can cause burns or death at high enough concentrations.

The wastewater also contains radioactive compounds like radium 226, a known carcinogen, which has a half-life of 1,600 years.

The company estimates the fans would run for up to 4,380 hours a year, or 12 hours every day, running through about 631m gallons of contaminated water a year.

“Aeration is not the answer,” said Wilma Subra, a prominent environmental scientist and toxics expert who has been closely monitoring the case. “Anything deposited on that community will be there forever.” Members of Rise St James were surprised to learn that the company was still pursuing its fan plan after the LDEQ first rejected the idea this summer. “That’s a shame, I thought it was a done deal with the fans,” said Sharon Lavigne, director and president of Rise St James. “We still have to fight.”

Facebook Twitter Pinterest Gail Lebouef, Sharon Lavigne, Barbara Washington and Myrtle Felton. Photograph: Lauren Zanolli

The sinkhole

Residents point to Mosaic’s history as cause for further concern.

In August 2016, a sinkhole opened up under a gypsum stack, similar to the one in St James, at Mosaic’s Mulberry phosphate processing plant in Florida. About 215m gallons of polluted process water drained into an underground aquifer. Mosaic informed Florida’s department of environmental protection (DEP) right away about water loss, but didn’t immediately disclose the sinkhole. Almost three weeks passed before either Mosaic or the DEP informed the public, despite the fact that the sinkhole was initially considered a potential threat to the public’s water supply.

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The company has been under the consent decree with EPA and the Department of Justice since 2015 for violations related to hazardous waste disposal at its six sites in Florida and Louisiana, including the Uncle Sam facility.

Some activists have called for a complete closure of the plant in light of January’s news about the wall of the gypsum shifting.

Lavigne of Rise St James said any plant should be closed down that is releasing toxic emissions, which have been linked to cancer and other potentially fatal health issues. “If it’s killing us, shut it down,” she said.

Environmental racism

The Mosaic issue is one of several facilities that Rise St James and other advocacy groups say have caused a slow-motion environmental and public health disaster erasing the majority-black population here.

Rise and affiliated advocacy groups claimed a surprising victory in September when Wanhua Chemical withdrew its approved application to develop a $1.25bn petrochemical facility nearby.

The group has turned its attention to stopping a $9.4bn petrochemical complex being developed in the area by Taiwanese company Formosa Plastics Group. If approved, that project alone would effectively double chemical emissions in the area.

“We’re fighting for our life,” declared Lavigne. She said recent blood tests found aluminum linked to industrial pollutants in her body, and doctors are now monitoring her liver for any health complications. “They’re killing us off, one by one.”