The Coral Gables Problem Beneath the Surface

Nearly Half of Coral Gables Residences are on Septic Tanks. Many May be Leaking. As Sea Levels Rise, How Big a Problem is That?

Known for Mediterranean Revival architecture, tree-shaded boulevards and winding waterways, fine dining and graceful living. Coral Gables has earned its reputation as a world class city. Often cited in national surveys as among the most beautiful towns in America.

Yet just beneath the surface in the City Beautiful lie some troubling problems. Potentially hazardous, dangerous problems. “This is a hot topic we’ve been talking about for years,” says Vice Mayor Vince Lago of the thousands of septic systems on the properties of Coral Gables homeowners and businesses. “There are lots of tanks that are not properly maintained, or not maintained at all. And when talking about our drinking water or Biscayne Bay, that’s a concern.”

In Coral Gables, an estimated 7,000 properties, most of them single-family residences, are on septic systems. That means between 40 and 50 percent of the city’s 51,000 residents, flush toilets and drain grey water from sinks and washing machines into concrete boxes buried in the yard, according to city utilities director Jorge Acevedo. If the systems are working properly so, the liquid waste passes through a drain field, before be filtered through a layer of dry soil. Most commercial properties in the downtown area and along the U.S. 1 corridor, along with a few hundred single-family homes, near Granada Golf Course and also along Old Cutler Road, are hooked up to a sewer system that the city owned and operated by the city. The city sends the waste for treatment to the Miami-Dade Water & Sewer Department. The county also provides Gables with its water, and handles billing.

In Miami-Dade County, where sea levels have already risen four inches since 1994, more than 105,000 residential properties still use septic systems, according to a 2018 Miami-Dade County report. More than half of those systems, 58,349, are periodically compromised – i.e., not working properly during storms or wet years, the report said. By 2040, that number is expected to increase to more than 67,000.

How Septic Tanks Work:

Coral Gables
House waste water flows to the septic tank. Then the septic tank acts as a treatment plant and removes the bacteria. After, the Clean water percolates down into the groundwater.
Coral Gables
The “effluent,” fills most of the tank. After that, aerobic bacteria breaks down the organic material in the effluent. So, effluent flows through a baffle to the drain field where it is allowed to seep into the surrounding gravel.

Caring for your septic tank

  1. Have the system pumped out and inspected by a professional every three years.
  2. Grow grass or small plants above the system to hold the drainfield in place.
  3. Do not put grease or non-biodegradable materials down the toilet or sink.
  4. Don’t flush paint thinners, polyurethane, anti-freeze, pesticides, disinfectant, water softeners or other strong chemicals.
  5. Never flush indigestible materials. Such as diapers, cigarette filters, feminine products, cat litter, or plastic.
  6. Do not plant trees within 30 feet of your system or park/drive over the system.
  7. Do not do all machine washing in one day, to avoid overwhelming the system with excess wastewater.

Source for care:  Miami Waterkeeper

The Sea Level Rise

Sea levels are expected to increase an additional two to six inches by 2030, concludes the county’s report, entitled “Septic Systems Vulnerable to Sea Level Rise.” As groundwater levels rise, “septic systems cannot function as designed. Improperly functioning septic systems can pose an immediate public health risk,” the report says. “There are also many financial and environmental risks, including contamination of the freshwater aquifer, which is the community’s sole source of potable water.”

South Florida’s hydrogeology – the movement and distribution of underground water – is one of the most complex in the world. Underneath the large urban area that hugs the east coast is a layer of porous limestone connecting the groundwater supply directly to Biscayne Bay and the Atlantic Ocean, says Douglas Yoder, deputy director of the Miami-Dade Water and Sewer Department.

“As sea levels rise, we need a foot of difference between the elevation of fresh and sea water to make sure salt water doesn’t move inland,” says Yoder. Salt water intrusion would pose a threat to both our drinking water and the built environment, including septic tanks. And, as the county’s vulnerability study found, “Septic systems were not designed with the assumption that groundwater levels would rise gradually over time.”

What the City Says

For Coral Gables, well-known for zealously protecting its upscale image with tough zoning and building codes, and for championing green initiatives, septic tanks present a quandary. They represent, as Lago says, a classic illustration of out of sight, out of mind. If septic systems are working properly, no problem. But the city cannot afford to ignore the possibility that leaking tanks may be contributing to environmental pollution, and neither can the city afford to mitigate the threat by installing a city-wide sanitary sewer system.

The cost of converting all of Miami-Dade County – including Coral Gables – from septic to sewer would top $4 billion, and take years, according to the latest estimates. Were the Gables to extend its own sewer system to homes now on septic, the cost would also be stratospheric.

“The concern is trumped by cost, which is so exorbitant it’s a little disheartening,” says Lago. “We are getting limited cooperation from the [Miami-Dade] county and the state. That leaves us in a tough position. But, it’s a priority we have to take seriously.”

The city is now talking to Florida Power & Light officials about putting power lines underground, part of a 30-year, multi-billion-dollar plan authorized by the Florida legislature in 2019. “There is no way under our current financial state that we can undertake undergrounding [power lines] and transitioning from septic to sewer,” says Lago.

What can be done, Lago says, is exploring legislation that would require septic systems be maintained, paired with a program of incentives encouraging homeowners’ compliance. “Do a simple analysis of the septic, to see it’s performing appropriately, to make sure we’re not contaminating the aquifer or the environment,” says Lago. “Residents would be incentivized, not penalized.”

Coral Gables
Florida International University (FIU) sample water quality as of means of pinpointing the sources of nutrients that run off into ground water and Biscayne Bay

At the same time, Lago urges citizens and legislators to support Everglades restoration. City officials are talking to state and federal officials about the money necessary to extend the sewer system throughout the city, according to Commissioner Patricia Keon. “We know that conversion [from septic to sewers] will need to start,” says Keon. “We need to start looking for funding sources. These are billion-dollar issues, large amounts of money.” (Monroe County recently wrapped up a massive project to install sewer lines to serve the entire 120-mile island chain, a project that began with legislation in 1999 and cost more than $1 billion).

Keon says “there is no immediate problem” with the Gables’ septic systems now because most of the city is on high ground. However, she adds, “we know that in the future it will be a problem. We acknowledge that as sea levels rise, and given the porosity of the whole state, it could create an issue. We have a 30-year window to address this issue.”

The Risk to the Biscayne Aquifer and Bay

Miami Waterkeeper, a public interest group, thinks the situation is much more urgent. Of the more than 105,000 septic tanks in Miami-Dade County, including those in Coral Gables, “many are not functioning properly,” says Kelly Cox, general counsel of the nonprofit organization with a mission to protect South Florida’s watershed through science and citizen engagement.

In addition to sewage leaking from septic systems, runoff from storm drains carry effluent and nutrients that can seep into the Biscayne Aquifer and eventually reach Biscayne Bay, Cox said. These excessive amounts of nitrogen and phosphorus cause algae to grow faster than the ecosystem can sustain, reducing or eliminating the amount of oxygen in the water and blocking sunlight.

“We are moving a lot of nutrients into the waterway and the bay,” says Cox. “And Coral Gables, with the number of parcels on septic and its proximity to the bay, make it a hotspot.” Among sites monitored weekly by Miami Waterkeeper is the swimming pond at Matheson Hammock in Coral Gables. The group samples the water for enterococcus, bacteria frequently associated with sewage and which can both cause gastrointestinal problems and serve as an indicator of other sewage-related pathogens. Test results are posted on the website

Just how much pollution might be leaking from Coral Gables septic systems may be revealed in a multi-year study to be led by researchers at Florida International University. The study, for which the city has budgeted $1.2 million over next five years, will sample water quality as a means of pinpointing the sources of nutrients that run off into ground water and Biscayne Bay, according to FIU scientist Tiffany Troxler, the lead investigator. That information can then be used by city officials to manage the canal system and plan for sea level rise. Other agencies involved in the study include, Miami Waterkeeper, the National Oceanic and Atmospheric Administration, the University of Miami and the county’s Department of Environmental Resources Management.

“If you think about it, no septic tank is going to be 100 percent efficient,” Troxler says. The study, which is to begin this summer, will use chemical tracers and DNA fingerprinting to determine how much humans contribute to the bacteria found in ground water. “Coral Gables wants to understand how the city can manage potential water quality issues,” says Troxler.  “This has economic value for recreation and tourism, and could minimize the incidence of algae blooms.”

Kelly Cox from Miami Waterkeeper, collects samples at Matheson Hammock for testing.

The Environmental Impact

The environmental impact of faulty septic systems is difficult to track, says Acevedo, because the systems are the property of homeowners, regulated by the state Department of Health. “We don’t do inspections or tests,” says Acevedo. “We are really lucky in the city because in the lower areas, like south of Old Cutler, homes are on sanitary sewer,” he added. “And most homes with septic are on higher ground.”

The exception is Kings Bay (cq), a gated neighborhood adjacent to the bay where many homes are on septic systems and elevations are low. Public works officials say they are not aware of any issues with septic systems in that neighborhood.

Prior to the November elections, Miami Waterkeeper, in partnership with the Miami Foundation plans to launch a campaign to inform voters about the importance of converting septic tanks to sewers. “We want to guide the conversation, make this a priority issue, a key component of environmental resiliency,” says Cox.

“Conversion is not easy. It is a significant undertaking; it means right of way acquisition and tearing up roads,” she says. “But we need to start thinking more critically, and decide what is going to work. We need to start making these decisions now.”