A potential environmental disaster might be looming in St. James Parish. 

A nearly 200-foot wall of gypsum encasing a lake of 720 million gallons of acidic water is moving. The acidic water, coming from Mosaic Fertilizer's Uncle Sam plant in Convent, could potentially spill out into the surrounding cane fields and even find its way to the swamps around Blind River if the wall collapses.

On Jan. 10, Mosaic advised state regulators in a letter that a wall of one of their gypsum stacks is moving and that the company was taking immediate action. The 1,500- to 2,000-foot-long section of the north wall of the gypsum stack is shifting at a rate of about a half inch per day.

The movement is uneven though. Some parts move and stop, then other parts shift. In total, the farthest that any section of the wall has moved is 13 feet to the north toward La. 3214. Company officials think the wall has been moving since the spring, though the shifting wasn't discovered until late December and early January. 

What is gypsum?

Phosphogypsum, or gypsum, itself is a solid waste. Companies like Mosaic mine phosphate and extract the phosphorous for fertilizer. The gypsum is an unwanted byproduct of the extraction process. It is difficult to reuse due to its small amounts of radioactivity.

The process that is used to make phosphate fertilizer results in the acidic wastewater and lots of phosphogypsum, an unwanted byproduct with trace radioactivity and other contaminants. The acidic process water, which has the strength of lemon juice or vinegar, is the major concern for company officials and state regulators. Both the gypsum and the process water exist under a federal exemption that allows them not to be treated under law as a hazardous waste. But company officials openly say the water is a "hazardous material" that they don't want to escape into the broader environment.  

Though the moving gypsum wall has had no leaks, according to state regulators, Mosaic has taken actions to stop the wall's slow march. The fertilizer company plans to place mounds of dirt and use their weight slow the leading edge of the shifting wall. Mosaic has also begun draining 10 million gallons of water per day from a lake atop the gypsum pile about half as large as the LSU Lakes. The measures aim to lessen the weight of the lake that is pushing the wall outward.

Mosaic is not a stranger to gypsum problems. In 2016, a Florida sinkhole opened up under a gypsum pile and swallowed up 215 million gallons of contaminated water, which released into the ground below. 

How tall is the gypsum wall?

Looming at 200 feet in the air, the towering white pile of waste near Convent supports and encases a giant pond of acidic process water from the fertilizer complex on the east bank of the Mississippi River, state permit documents show. Other ponds also hold process water or rainfall runoff from the pile at lower elevations on the man-made mound. 

What might happen if the wall collapses?

A sudden, catastrophic failure could release the acidic water into the surrounding site and possibly into surrounding lands and waterways. Officials acknowledged that such a major failure, if it did happen, could send the process water spilling into Blind River and the fresh water swamps surrounding it. Mosaic has hired a firm to model how water would flow from a catastrophic release, so the company can prepare to prevent the acidic process water from escaping the company's property.

Advocate staff writer David Mitchell contributed to this report. You can reach him at dmitchell@theadvocate.com.