Eric Weiss, director of the city’s wastewater department, said such prolonged rainfall soaks the ground and raises the water table above the underground wastewater pipes, where it finds its way into cracks, gaps and other openings. It fills the pipes to overflowing — a process called infiltration.
The city has 220 wastewater pumping stations but they couldn’t empty the pipes fast enough as some inches of rain fell over 11 days in parts of the Tampa area.
“The wastewater system didn’t have enough time to recover and get rid of the wastewater,” Weiss said.
Once filled, more water causes the pipes to overflow — often straight up through the small openings in manhole covers, like miniature geysers.
The city of Tampa plans to send cameras inside its wastewater system soon to find which pipes need to be repaired or replaced, prioritizing “the worst of the worst,” according to Weiss.
Along with human waste overflowing from the sewers, nasty stuff from the surface like pesticides and animal feces also are washed into the water by the rain, spreading the bacteria-laden mixture far and wide.
Some of that mixture can contain E. coli from the raw and untreated wastewater overflow. The city does try to treat the overflow on the surface with lime, a chemical that neutralizes organic matter, but it couldn’t keep up with every flooded area.
“Would you want to be in there?” asked Steve Huard of the state Health Department in Hillsborough County, repeating the advisory for people to stay out of the mess.
Huard shakes his head at images of children and adults splashing, fishing and paddling in streets that have become rivers. Infection is a special risk for anyone with so much as a scrape.
“Literally everything that ends up on that surface is in that water,” he said.
Fortunately, Weiss said, E. coli dies after one or two days or when areas dry up.
Surface cracks and other imperfections are a particular problem in wastewater pipes that are as old as 80 to 100 years, Weiss said. The age of the pipes combined with the volume of water contributed to the sewage overflow.
The city spends $1 million to $2 million a year on wastewater lines and manhole repairs and conducts camera inspections along each stretch at least once every seven years — the industry standard.
Replacing and repairing old and damaged pipes would help reduce sewage overflow but probably not eliminate it, Weiss said. The system was designed to handle large afternoon showers, not sustained downpours day after day.
He said he knows of no system that could protect against overflows under these conditions, adding that the problem “isn’t unique to any city of our age with aging infrastructure.”
A proposal to raise homeowner fees fivefold for an overhaul of the aging stormwater system will help stop street flooding but not the wastewater overflow, Weiss said, because the two systems operate separately.
Weiss said when the wastewater does reach the treatment plant, it’s treated in accordance with environmental permits and discharged, or recycled, into the bay.
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