Riverview, Fla., Fertilizer Plant Digs in To Prevent Spills
Dec. 7RIVERVIEW, Fla. Bulldozers and dump trucks are moving thousands of tons of earth at the former Cargill phosphate processing plant, hoping to prevent a recurrence of the wastewater spill triggered by Hurricane Frances.
When the work is finished, there will be three new emergency holding ponds at the plant, now called the Mosaic Co., capable of holding 500 million gallons of the highly acidic water. Plant managers will be able to use the extra storage capacity to lower water levels in the impoundment atop a 180-foot-high phosphogypsum stack.
State officials say water levels in the gyp stack were too high when Frances roared through the area Sept. 5. The hurricane's winds created waves that broke a dike atop the stack, spilling 65 million gallons of the acidic and radioactive water into Archie Creek, which empties into Hillsborough Bay.
Federal scientists are assessing the environmental damage to Hillsborough Bay and the surrounding mangroves, marshes and wetlands. That assessment should be finished in several months, and a restoration plan will be released for public comment in the spring.
The new storage ponds were included in a consent order the Florida Department of Environmental Protection issued to the company after the storm. Other safety measures the company is to take include increasing the use and reuse of water at the plant and installing a water treatment system. DEP officials say the order, still being amended, will include a fine, as yet undetermined.
Water is important in turning raw phosphate rock into fertilizer. Water and sulfuric acid are mixed with ground up phosphate rock to form a thick slurry. The sulfuric acid is used to break the phosphate away from the calcium. In Florida, the two always are bound together.
The mudlike slurry then is pumped onto a large table with a filter. Water is used to wash the mixture through the filter. What comes out the other side is liquid fertilizer.
Water is used again to take the waste product, calcium sulfate, also known as phosphogypsum, to the top of the gyp stack for storage.
The water is constantly being moved at the plant. During the dry season, the plant might need to import water to replace what is lost through evaporation. During the rainy season, water storage becomes a problem that can ramp up to a crisis as it did in September.
Mosaic finished two 10-acre holding ponds in October on top of an inactive gypsum stack. Each pond will hold about 65 million gallons of water. A third pond, 60 acres, is being dug on the stack that will hold 350 million to 400 million gallons.
The new ponds will allow Mosaic to decrease the distance between the stored water's surface and the top of the dikes. That distance is called freeboard.
"What they're building is a new bathtub," said Chris Dunn, head of the water management division at the Hillsborough County Environmental Protection Commission.
"As they move this water into the second bathtub from the first bathtub, they're improving the freeboard so the system can operate safely," Dunn said.
Mosaic Vice President Gray Gordon said the company also is installing equipment that will use heat created during fertilizer production to speed evaporation of process water. The system will be capable of evaporating 500 gallons a minute, he said.
"That's really the only way ... that we can get rid of water," Gordon said.
Mosaic is building another, smaller dike inside the larger outer one. This new wall will buffer the outer dike from the kind of wave action that caused the spill in September.
Process water contains a number of pollutants, but the most damage is caused by acid and nitrogen. The acid causes the most immediate damage, killing fish and mangroves. The nitrogen causes algae to grow. Large algae blooms consume oxygen, killing fish and depriving sea grasses of sunlight.
After the September spill, the company dumped truckloads of lime into Archie Creek, to neutralize the water's acidity before it reached the Bay. Nothing could be done to neutralize the nitrogen.
Now, as part of the consent order, the company must install a treatment system that lowers acidity and removes nitrogen. The company is considering a reverse osmosis membrane system, similar to the system used at the abandoned Piney Point phosphate plant in Manatee County.
"They're going to have to comply with water quality standards," said Phil Coram, DEP's chief of mining reclamation. "Any type of water system discharging near Tampa Bay would have to have extremely low nutrient levels."
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