TAMPA – More than 41 million gallons of acidic wastewater spilled by a fertilizer company into a Hillsborough Bay tributary could cause significant environmental damage.

Cargill Crop Nutrition, a unit of Cargill Inc., faces the possibility of regulatory as well as ecological fallout from the spill that resulted from a reservoir breach amid Hurricane Frances on Sunday.

“It’s a serious spill,” Vice President Gray Gordon told a news conference Monday at company offices north of Gibsonton. “We’re very upset about this, very concerned.”

At one point, he apologetically characterized it as “a 10 on a scale of 10.”

That doesn’t mean it’s a worst-case scenario for public health or safety, authorities emphasized. The environmental threat is to fish and other wildlife in and around Archie Creek and Hillsborough Bay, not to people, pets or livestock in the area.

In Cargill’s view, though, the spill was about as bad as it gets – an unexpected event that caught the company unable to contain it.

An overflow ditch couldn’t handle the spill, and for a while the company ran out of a caustic solution used to buffer acidity in the escaping wastewater. Then, crews couldn’t begin to make repairs because the lingering storm made work along the berm too risky.

It was midday Monday before Cargill announced that water had stopped flowing through the breach. Even then, with workers beginning to pump the overflow elsewhere on its property, the creek continued to receive a discharge that local authorities said could amount to millions of additional gallons.

“We haven’t determined damage at this point,” Gordon said, as government scientists began drawing water samples from the creek and the bay to assess potential harm.

Phosphate wastewater is high in nitrogen and phosphorous, which enables algae to thrive. That can reduce the amount of oxygen in the water, killing marine life.

Rick Garrity, director of Hillsborough County’s Environmental Protection Commission, said it could be days or weeks before a solid assessment is available.

“Hopefully, they buffered a significant amount of the discharge, but I understand a lot went into Archie Creek unbuffered,” he said. “If we find significant impact, we’ll keep following up.”

Other follow-up is likely, too. Regulators could make the company pay for environmental damage and change its water retention design.

Garrity said his agency and the state Department of Environmental Protection had issued recent warning notices to Cargill about the levels of wastewater being stored on the property in light of heavy summer rains.

Cargill reported rainfall at 17 inches above normal for July and August.

“We’ll definitely get directives, and there could be fines,” Gordon said when asked about a regulatory response. “We’re going to have to look at not only the dike’s width but also the height.”

The dike “should not have failed,” Garrity said. “I think absolutely a likely outcome will be a restudy of the design to add an extra margin of safety.”

How It Happened

The design is common to the phosphate industry across Central Florida.

Processing phosphate into fertilizer creates a byproduct called phosphogypsum, an earthen substance with low levels of radioactivity that is stacked in sprawling mounds by bulldozers and other heavy equipment.

In the center of the mounds are shallow, bowl-shaped retention reservoirs to hold the wastewater while it evaporates. As each gypsum stack is piled ever higher, the bowl’s rim is supposed to remain substantive enough to serve as a dike against leaks.

The gypsum is compacted by its own weight, hardening into something closer to the consistency of limerock than dirt, said Parker Keen, Cargill’s land manager. That’s why the dike – always the softest, top layer – gave way horizontally instead of vertically.

What began as a 6-foot-wide gash, created by storm-driven waves in the reservoir at midday Sunday, grew quickly to 30 feet across, and finally to 50 feet, Cargill reported.

The reservoir holds an estimated 150 million gallons atop a gypsum stack that has been piled to 180 feet high, on its way to a permitted height of 250 feet.

As water burst from the breach, it poured down to an overflow ditch that encircles the stack and is capable of holding 30 million gallons. Officials worried about keeping that ditch intact soon opened a valve to release at least some of the flow into the creek.

The valve is capable of releasing 30,000 gallons a minute, so multiplying that by the approximate 24-hour release period produced the estimate of more than 41 million gallons dumped into Archie Creek.

Environmental Damage Uncertain

The volume is in the range of the more than 50 million gallons of acidic wastewater that escaped from a burst dam at Mulberry Phosphates in 1997. That poisoned about 35 miles of the Alafia River and killed an estimated 3.1 million fish.

Gordon said he did not believe his company’s spill would be comparable because Cargill moved quickly to treat the escaping water with caustic soda to lower acidity.

Yet Cargill was not prepared with enough of the caustic solution, and when its supply ran out, more had to be trucked in. Details of how much time elapsed remained sketchy Monday, and Gordon conceded this could be another area of regulatory concern.

Garrity said Cargill has been among its industry’s better corporate citizens, but that won’t prevent public criticism.

Karen Wagner, who lives along the banks of the Alafia River in Riverview, said Sunday that she was worried about contaminated water making its way up river in above-normal tides.

After an IMC Phosphates pond breach spilled millions of gallons of muddy water into Mizelle Creek on Aug. 18, five days after Hurricane Charley, Wagner said she spoke to Cargill representatives who assured her they were prepared for any weather.

“Obviously they were not prepared,” she said. “We didn’t even get 4 inches of rain, and this happens.”

Reporter Yvette C. Hammett contributed to this report. Editor John Vaughan can be reached at (813) 259-7524.