Miami septic tanks failing due to sea rise
MIAMI — Miami-Dade has tens of thousands of septic tanks, and a new report reveals most are already malfunctioning — the smelly and unhealthy evidence of which often ends up in people’s yards and homes. It’s a billion-dollar problem that climate change is making worse.
As sea level rise encroaches on South Florida, the MiamiDade County study shows that thousands more residents may be at risk — and soon. By 2040, 64 percent of county septic tanks (more than 67,000) could have issues every year, affecting not only the people who rely on them for sewage treatment, but the region’s water supply and the health of anyone who wades through floodwaters.
“That’s a huge deal for a developed country in 2019 to have half of the septic tanks not functioning for part of the year,” said Miami Waterkeeper Executive Director Rachel Silverstein. “That is not acceptable.”
Septic tanks require a layer of dirt underneath to do the final filtration work and return the liquid waste back to the aquifer. Older rules required one foot of soil, but newer regulations call for double that. In South Florida, there’s not that much dirt between the homes above ground and the water below.
“All those regulations were based on the premise the elevation of groundwater was going to be stable over time, which we now know is not correct,” said Doug Yoder, deputy director of Miami-Dade County’s Water and Sewer Department. “Now we find ourselves in a situation where we know sea level has risen and continues to rise.”
Sea level rise is pushing the groundwater even higher, eating up precious space and leaving the once dry dirt soggy. Waste water doesn’t filter like it’s supposed to in soggy soil. In some cases, it comes back out, turning a front yard into a poopy swamp.
High tides or heavy rains can push feces-filled water elsewhere, including King Tide floodwaters — as pointed out in a 2016 study from Florida International University and NOAA — or possibly the region’s drinking supply.
In total, there are about 108,000 properties within the county that still use septic, about 105,000 of which are residential. The vast majority (more than 65,000) of the septic systems are in unincorporated Miami-Dade.
Miami Gardens, North Miami Beach, Palmetto Bay and Pinecrest have the most of any city, at about 5,000 each.
Some of those cities will see hundreds more septic tanks experiencing yearly failures within the decade, like North Miami Beach, which has 2,780 homes with septic tanks with periodic issues now. By 2030, that is expected to jump to 3,751.
The report did not forecast past 2040, when the region is expecting around 15 inches of sea rise, a number that is predicted to creep exponentially upward over the decades.
“The best response is sewer extension, but obviously that infrastructure takes quite a bit of planning and time,” said Katherine Haggman, the county’s resilience program manager.