Florida Using Deep Injection Wells for Heavily Treated Sewage Wastewater to Mitigate Effects on Coastal Ecosystems, Including Red Tides: Stormwater Disposal Rates Are Rising with Sea Level Rise

     Heavily treated “reclaimed” water in Florida may have three destinations: 1) sprinklers that water lawns, golf courses, and parks; 2) discharges into local waterways; or 3) pumped 1,000 feet underground into deep disposal wells. The state recently passed a law that prohibits discharge into the environment. Discharges of treated sewage wastewater are thought to have aided recent seagrass die-offs and red tide outbreaks. This has made injection wells more common, and plans are to drill more of them. However, the disposal zone is part of the same aquifer system as the drinking water, but below it, presumably separated by an impermeable aquitard; still, it is not too far in vertical distance from the drinking water aquifer. It sounds like it could be risky to me. It would have been better to dispose of it in a deeper zone. However, the risks likely depend on how much water is disposed of in the zone and how toxic or contaminated the water may be. Having been “heavily treated,” it should be fairly clean.

     The possibility of potential connections between the two aquifers could be a concern, so it depends on the groundwater geology as well, which should be closely evaluated and monitored. The older disposal wells in the area have had no problems, but one in the Florida Keys did.

     Another issue is well integrity. This can probably be assured with good contractors with experience in the area,

“South and Central Florida’s deep injection wells bury treated wastewater and commercial byproducts — like what emerged from the Piney Point phosphate plant spill amid a devastating red tide breakout in 2021. The wastewater is pumped into a salty zone of the lower Floridan Aquifer, a limestone formation separated from the upper aquifer, which holds most of the state’s drinking water supply.”

“It’s supposed to stay there, but experts aren’t sure if it does.”

     Currently, there are about two dozen injection wells disposing of this water in operation, and ten more have been proposed or are being constructed. Local authorities have until 2032 to dispose of the excess wastewater.

     An article in the Tampa Bay Times by Jack Prator gives St. Petersburg disposal well history as an example.

“St. Petersburg was an early adopter of injection wells in the late 1970s, though in the decades to follow, unpopular wastewater discharges would discolor the city’s relationship with the controversial method of waste disposal.”

“But storm surge and sunny day flooding that threaten homes have prompted a new use case for wells: stormwater disposal. St. Pete already runs 15 deep wells that dispose of half the city’s wastewater.”

“In total, St. Petersburg produces 11 billion gallons of treated wastewater each year, according to the city. It’s enough to fill 44 Tropicana Fields.”

“In 2016, the city discharged 220 million gallons of wastewater that hadn’t been fully treated into Tampa Bay and other waterways. It spurred an investigation by state environmental officials, who enforce limits on how dirty the water going into waterways and wells can be.”

“Three years later, St. Petersburg officials again broke state law by pumping 21 million more gallons of this wastewater into its deep wells over more than a yearlong period.”

     A local Sierra Club affiliate raised concerns about assessing environmental damage, and public engagement and trust. However, they did acknowledge that disposal wells are preferable to surface water disposal.  

     As noted, St. Petersburg hopes to drill disposal wells mainly for stormwater management. This also protects local homes from flooding during storm surges. Thus, the disposal wells can be seen as climate and extreme weather adaptation engineering projects.

 “Our focus is moving water out of neighborhoods that are difficult to drain in order to protect homes,” Tankersley wrote in an email. “Sometimes moving the water underground might be the only solution to avoid flooding other neighborhoods.”

     Pinellas County officials are planning to drill disposal wells. One noted:

“Other cities and counties in the state have been doing it for decades without any problems whatsoever.”

     The city of Largo in the Tampa Bay Estuary is planning to drill two disposal wells “to divert 6 million gallons of treated effluent from Old Tampa Bay, which has long been afflicted with nutrient pollution, poor water circulation and struggling seagrass.” They plan to drill at the water reclamation facility, which reduces pumping energy use and cost. Basically, it’s a Tampa Bay Estuary restoration project. Studies of the estuary indicate damage from past wastewater discharges.     

 

     Unknowns for deep disposal wells include the migration rate of injected wastewater with pressure in the aquifer and potential for fracture communication.

   

References:

Pinellas governments need to get rid of toilet water. They’re going underground. Jack Prator. Tampa Bay Times. August 20, 2026. Pinellas governments need to get rid of toilet water. They’re going underground