Flooded streets have become such a way of life in South Florida that most people wade right through the puddles. Sometimes, when the ponds are a bit deeper, they even pull out kayaks, paddleboards or wakeboards.
That makes public health experts cringe because that floodwater is likely pretty gross, often tainted with human and animal waste, among other foul things. It’s so gross that Miami-Dade County regularly warns residents to stay out of it or scrub up after touching it.
“It is absolutely full of bacteria and god knows what else,” said Rachel Silverstein, Miami Waterkeeper. “I don’t even want to think about all the industrial runoff.”
Exactly how gross isn’t clear, however. No agency monitors it and there haven’t been published research results about South Florida’s floodwaters in years. All the water-quality monitoring in Miami-Dade — from the county to nonprofits to academics to the state — focuses on canals and Biscayne Bay, not the street floods that regularly occur after heavy rains or high tides.
And with an extra foot of sea level rise on the horizon by 2040, Miami-Dade residents will probably be wandering through many more floods in the near future.
Sewage spills post-storm
Beyond the animal waste and chemicals in typical runoff, failing septic and sewage systems can also add to the nasty factor of floodwaters. The intense rains caused by the early June storm overran the troubled sewage treatment system in Miami-Dade, which is working with the federal government on a $1.6 billion, 15-year plan to stop spilling sewage into Biscayne Bay.
More than a million gallons of raw sewage spilled during and after this month’s storm. Most of that came from the Virginia Key Wastewater Treatment Plant, which was overwhelmed when intense rainfall doubled the amount of water in the system.
Twelve other spots around the county spewed sewage too, from Miami Gardens to Golden Beach to Homestead. Residents watched in disgust as manhole covers popped off (or were yanked off by residents seeking flood relief) and tampon applicators, condoms and raw human waste floated down their streets.
The sewage spills led to no-swim orders and beach closures, some of which weren’t lifted until nearly two weeks after the storm. They’re only removed after counts of enterococci bacteria, a sign that water could be tainted with poop, fall to an acceptable level for two days in a row.
Four days after the storm, Miami Waterkeeper recorded bacteria levels 1,000 times higher than safe levels in waters near Morningside Park, where a sewage system spilled about 1,600 gallons.
Mariner Drive in Key Biscayne, near the wastewater treatment plant spill, also registered levels nearly 40 times higher than safe standards.
“In all of Miami-Dade County our results for sampling lit up,” Silverstein said. “It was all these places that we don’t normally see. This is definitely a symptom of runoff from the storm.”
Another likely culprit besides sewage system failures is the thousands of leaky septic tanks across the county. Septic tanks need a few feet of dry dirt underneath them to filter and drain people’s waste. Sea level rise is pushing groundwater levels up, narrowing and even eliminating those dry zones.
Almost 9,000 of Miami-Dade’s septic tanks are already at risk of failing in a normal rainy season. With just a foot or so of sea rise, expected by about 2040, that number jumps to 13,500. This storm pushed groundwater levels up as much as five feet in some parts of the county and brought water levels nearly to the surface in others, according to the U.S. Geological Survey data.
The issue of leaky septic tanks after a flood is so well known that Miami-Dade’s Department of Health once suggested that residents with failed septic tanks consider renting a portable bathroom to use, or simply leaving their home until their bathrooms functioned again.
“With our issues with septic tanks and failing sewers, some of those juices come all the way up to the street,” said Henry Briceño, a geochemist at Florida International University. “People don’t know and they think they’re just walking in bay water.”
What's in that water?
Water testers in South Florida measure levels of enterococci bacteria, a sign of possible contamination from fecal matter. That means the water could carry disease-causing bacteria and pathogens.
The last notable time anyone in Miami Dade published information about floodwater bacteria levels appears to be 2015, when Briceño worked with the National Oceanic and Atmospheric Administration, the University of Miami and Nova Southeastern University to test the water Miami Beach pumped off the streets and into the bay following king tides.
They found high levels of bacteria in those waters, likely from leaking sewage pipes. Miami-Dade County followed up with more testing and found the same results, yet some city politicians tried to downplay the findings. Then-Miami Beach Mayor Philip Levine dubbed the study “sloppy science,” while providing no data to rebut the results.
But the study didn’t just involve Miami Beach. Briceño’s team found similarly contaminated water in Miami’s Shorecrest neighborhood and Fort Lauderdale’s Las Olas neighborhood, all from water pumped off the streets during high tides.
The same thing happens in flooded spots around the country. After Hurricane Harvey dropped more than 50 inches of rain on Houston in 2017, scientists tested floodwater on streets and inside homes. They found evidence of raw sewage and pathogens like Salmonella and C. perfringens, which can cause food poisoning.
In Charleston, reporters with the Post and Courier tested floodwater on streets near schools, public housing complexes and hospitals and found levels of E. Coli bacteria that were more than 60 times higher than state limits.
Why don't we test it?
Tiffany Troxler, with FIU’s Sea Level Solutions Center, has had volunteers collect samples of street flooding after high tides in Miami for several years, but has never published the results of those tests. She said she hopes to release that data — including bacteria levels — later this year.
Troxler’s work is the exception. Miami-Dade’s DERM doesn’t test the floodwaters of a street or in a park after a storm. But staffers do test canals, rivers and spots in the Bay regularly, and there’s an emergency response team that tests water quality whenever a sewage spill reaches the water.
Lisa Spadefina, assistant director at DERM, said that happened at four places after this storm: Morningside Park, Virginia Key, Hialeah and along the Miami River. She said there’s no requirement to report when a septic tank fails, so the county doesn’t have an exact picture of when and where those failures occur, or where that contaminated water goes — in part because “they’re generally on private properties.”
Waterkeeper doesn’t test floodwaters after a storm or high tide either. Silverstein said it’s difficult to plan for, difficult to fund and she worries about sending her team into potentially hazardous floodwaters.
Briceño, at FIU, said data on which spots are the dirtiest and what’s fouling them could help scientists and policymakers solve the most pressing problems first.
“Otherwise, we are just blindly making decisions,” he said.
