Massive pumps that flush floodwater from Miami Beach into Biscayne Bay during seasonal king tides are dumping something else into the bay: human waste.
A study that looked at tidal floodwater and water discharged from the island’s new pumps during the 2014 and 2015 king tides found live fecal bacteria well above state limits. In one case, levels were more than 600 times the limit. While some of the fecal matter was dog waste, scientists found higher levels of human waste that likely enter floodwaters from leaky old sewer lines or septic tanks.
Detecting human waste in urban floodwater is hardly unusual, but scientists say finding so much in a city facing dramatic projections for increased flooding as seas rise is cause for concern.
We are practically going to have flooding all the time.
Henry Briceno, Florida International University’s Southeast Environmental Research Center hydrologist
“We are practically going to have flooding all the time, so those pumps are going to be operating almost all the time,” said Henry Briceno, a hydrologist with Florida International University’s Southeast Environmental Research Center.
But city officials say the “snapshot” sampling isn’t surprising during king tides. But they also say the study does not acknowledge the “holistic” approach the city is taking by educating residents and businesses about pollution causes or note that Miami Beach is also replacing and upgrading sewage pipes and other parts of the system.
“Stormwater pipes are known conveyances of pollution. That is their job,” said Elizabeth Wheaton, the city’s environment and sustainability director. “Their job is to drain the city. So when you sample at the outfall, of course you’re going to find elevated levels of bacteria.”
The island currently floods about six times a year during seasonal high tides that typically occur in the fall. But that flooding is expected to become more chronic. In April, the Union for Concerned Scientists revised its estimate for flooding on the beach with new sea rise projections from the U.S. Army Corps of Engineers to about 380 times a year by 2045.
And the problem is not just one for Miami Beach. Up and down the coast, as seas rise, more urban water is expected to be flushed into coastal waters, putting at risk one of the state’s biggest tourist draws.
People don't realize that what's on the street almost certainly ends up in the water sooner or later.
Miami Waterkeeper and marine biologist Rachel Silverstein
“People don’t realize that what’s on the street almost certainly ends up in the water sooner or later,” Miami Waterkeeper and marine biologist Rachel Silverstein said in an email. “During Hurricane Sandy, for example, over 10 billion gallons of sewage spilled. Here in Miami Dade, we still have frequent sewage spills during heavy rains that aren’t even close to hurricane-level storms.”
Miami Beach is in the midst of a $500 million overhaul to its stormwater system that will eventually include about 70 pumps. So far, four have been installed, which the city unveiled in 2014 to rave reviews.
At the time, Briceno and a team of scientists from the National Oceanic and Atmospheric Administration and the University of Miami began sampling water to determine if the pumped untreated urban water had any impact on the bay. That first year, they found elevated levels of phosphorus, nitrogen and other pollutants that can trigger algae blooms toxic to marine life. To confirm the findings, they returned last year.
The number of Miami Beach floods expected to occur annually by 2045
The recent report took a closer look at the water’s contents, breaking down findings into fecal matter measured by water regulators and identifying both human and dog waste.
At four sites tested in 2015, which included outfall pipes, portable pump discharges and street water, every site had fecal levels above state limits. Along Indian Creek Drive, levels were 622 times as high. In 2014, a storm drain outfall at 14th Street measured 630 times allowed limits.
For now, tidal flushing has kept the dirty water from building up in the bay. Samples taken further from shore, the team found, was largely diluted, creating a kind of halo of pollution.
“Tidal flushing every day actually cleans up the water,” Briceno said. “That helps a lot so we don’t have a major problem. But those waters that are flushed out go to the coral reefs.”
Wheaton said the city has expanded its own monitoring to get a better picture of how much dirty water is leaving the city and how tidal flushing affects it. The city is also trying to better educate the public about waste, including not dropping dog waste bags into storm drains. In neighborhoods packed with restaurants, grease has also become a growing problem with blocked drains, so the city recently hired an additional inspector, she said.
“We all have a responsibility for the health of the bay. The government is just one entity,” she said. “We need to encourage our businesses and residents to to be part of the solution.”
But over time , Briceno worries so much polluted water will start to take a toll on the bay as the city continues to grow. He also worries about people unwittingly wading through dirty flood water and said the city needs to do a better job of informing the public about health risks.
“I recognize that they are doing a heck of a job compared to other cities, but we need to address this problem,” he said. “It could be a problem with public health and I know it causes problems to the bay’s ecosystem. And those waters are protected.”
Briceno believes the city should consider injecting the wastewater beneath the Biscayne Aquifer into the boulder zone, a fix he estimates would cost about $7 million. But Wheaton, who said the cost would be closer to $10 million per well, said the cost is too high.
“Do elevated levels of bacteria concern us? Yes,” she said. “But we also need to look at everything we’re doing and not just a moment in time.”
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