A ditch digger laying pipe near Bruce B. Downs Boulevard eight or nine months ago struck and cracked a major city sewer line that last week finally erupted into a spill of 4 million gallons of raw sewage into an environmentally sensitive area, officials said today.
The spill swelled into Trout Creek, said a report issued today. The plume flowed down the creek into the Hillsborough River, but each day the fecal coliform contamination decreased through dilution and sunlight.
The report from Tampa's sewer department was submitted this afternoon to the Florida Department of Environmental Protection and the Hillsborough County Environmental Protection Commission.
Sewer department director Ralph Metcalf today said there is no threat to the public's health.
He said the cost of fixing the break and subsequent cleanup so far has amounted to about $200,000. The damage was done several months ago, he said, but wasn't detected until March 15. The damaged two sewer lines - one 18 inches wide and one 24 inches wide - were fixed within days of the spill's discovery. Crews also sucked up nearly 70,000 gallons of the spill and returned it to the sewer system, the report said.
Additionally, markers will be placed along Bruce B. Downs Boulevard to guard against future damage by road-widening construction.
Immediately, after that, scientists began keeping track of the plume as if flowed down Trout Creek toward the Hillsborough River. They have been taking samples of water and measuring the fecal coliform content. At its peak in Trout Creek, a sample contained about 2 million coliform colonies in a milliliter of water, Metcalf said.
As the plume made its way downstream, levels decreased. Metcalf said the dilution of the creek and eventually the river caused the levels to drop significantly. The most recent reading from the Hillsborough River showed just 18 colonies per milliliter, he said.
Metcalf said scientists have determined that levels above 800 colonies per milliliter represent a health threat.
"We have been monitoring the fecal coliform levels in Trout Creek down to the river and beyond, as far south as the reservoir," he said, which is near Rowlett Park.
Metcalf said it took about six days for the plume to travel down the narrow Trout Creek, reaching the river on Tuesday.
"As that is happening, nature is taking its toll," he said. "The sunlight, for example, causes the colonies to die off. It is exactly what you would expect would happen. It's dying out. It's going away rapidly.
"It will not exist," he said, "by the time it gets to the reservoir."
Hydrologists had predicted that nature would dilute the raw sewage and render it nearly harmless by the time it reached the city's reservoir. Water from that reservoir is pumped into a water treatment plant that is designed to remove contaminants in the river water, including bacteria from sewage.
The pollution is not expected to cause long-term damage to the river or a large fish-kill, though algae blooms may be a result and a depletion of oxygen levels in some areas.
Still, signs posted along Trout Creek and Hillsborough River parks downstream from the spill warned people to stay out of the water and not to fish.