TAMPA - At least 41-million gallons of contaminated water have spilled from a Riverview phosphate plant into a creek that leads to Hillsborough Bay. Another 20-million could end up in the creek by today, officials said.
Cargill Crop Nutrition, a fertilizer manufacturer, mixed the highly acidic wastewater with a neutralizing agent, hoping to minimize its environmental impact. Company and government officials also counted on heavy rainfall brought by Frances to help dilute the polluted water.
But initial test results show the creek water was much more acidic than normal.
The spill poses no threat to humans, company officials said. But it was unclear Monday how badly fish and other wildlife would be harmed.
"It's a serious spill," said Cargill vice president Gray Gordon.
The problem was caused when a dike at the top of a 100-foot-high gypsum stack holding 150-million gallons of polluted water broke Sunday after waves driven by Hurricane Frances bashed the dike's southwest corner.
The water, which Gordon likened to diluted fertilizer, streamed from a 60-foot opening at the top of the stack down its side and into a stormwater ditch that runs around its 400-acre base. Cargill decided to open a valve and release water from the ditch into Archie Creek, after consulting with the state Department of Environmental Protection.
Releasing the water, Gordon said, prevents a break or overflow of the ditch, a situation that could cause an uncontrollable flood of polluted water.
The company initially put the amount of the spill at only 18,000 gallons. On Monday, however, officials said more than 60-million might be released by today.
Adding to the problems, the company ran out of neutralizing agent at some point Sunday, meaning untreated water may have escaped, Gordon said. Additional truckloads of the agent, caustic soda, were delivered to the Cargill plant late Sunday night.
Still, pH levels in the creek came in low Monday, indicating high levels of acidity.
"The treatment is ineffective," said Sam Elrabi, spokesman for the EPC. The levels, he said, "don't meet water quality standards that they have to meet in order to discharge."
At the point where Archie Creek meets Hillsborough Bay, the pH levels were measured at 3.1, Elrabi said. Normal levels are between 6.5 and 8.
In addition to treatment, Cargill took steps to limit the amount of wastewater it would have to release into the creek.
The company pumped some wastewater to a retention pond at the top of an old gypsum stack that has been inactive since 1990. Cargill also began pumping excess water to a 238-acre retention pond at its sprawling industrial site.
The acidic sludge stopped flowing from the top of the stack Monday, and crews temporarily closed the break in the dike.
Cargill makes fertilizer at the plant from phosphate. Gypsum is a slightly radioactive byproduct of the process, and is stored in mountainous stacks. Retention ponds at the top of the stacks hold water used to make fertilizer.
Gordon said the wastewater contains a tiny amount of radioactive material.
The release is likely to result in fines and requirements for preventive measures from the Hillsborough County Environmental Protection Commission, the DEP and the National Oceanic and Atmospheric Administration, said Rick Garrity, executive director of the EPC.
Environmental experts said it may take days to know exactly how badly wildlife will suffer.
Waterways around the western Hillsborough County shoreline are part of a highly sensitive ecosystem, said Holly Greening of the Tampa Bay Estuary Program.
It's a feeding ground and nursery for redfish, snook, tarpon, manatees, shrimp and crabs as well as birds such as herons, egrets and sandpipers.
Acidic water can hurt or kill such wildlife. And even if the acidity doesn't prove to be a problem, Cargill's Gordon acknowledged that the spill probably will raise nitrogen levels.
Nitrogen fuels algae growth that can rob the water of oxygen or block sunlight needed by sea grass, an important food source for manatees, Greening said.
The Tampa Bay area has struggled for years with accidents at phosphate plants.
In 1997, a phosphate plant in Mulberry dumped 50-million gallons of untreated acidic water into the Alafia River, killing millions of fish.
After a heavy rain Aug. 18, about 4-million gallons of muddy water ran from a retention pond at the IMC Phosphate plant in Keysville into a creek off the Alafia River.
Gordon said Cargill had been trying in recent weeks to reinforce the dike in anticipation of Hurricane Charley and then Hurricane Frances.
Dominick Gebbia, president of the south Hillsborough-based environmental group Save Our Bays and Canals, said Cargill should have expected a problem like this might arise during a hurricane.
Times staff writer Jay Cridlin contributed to this report.