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Florida sea level rise big problem for septic tank system

Dr. Mario Picazo
Meteorologist, PhD

Tuesday, January 15, 2019, 5:59 PM - Florida's Miami-Dade County relies heavily on septic tanks that require constant maintenance, but a new county study reveals that the situation will require even more attention as sea levels continue to rise.

Since 1994, sea levels have risen more than 10 centimeters and are expected to increase an additional 5 to 15 centimeters by 2030. The rise of sea water has brought higher groundwater levels in some areas and those will continue to rise over the long term.

When groundwater is higher than usual, septic systems cannot function as designed, with an immediate threat to public health. But there are other negative impacts, like the contamination of fresh water aquifers which provide potable water for thousands of residents.


Septic systems treat and dispose of wastewater from individual properties. The wastewater from kitchens, bathrooms, laundries, and other sources is gradually treated by allowing the wastewater to pass through the septic tank and, subsequently, the drain field. A total of 108,000 properties in Miami-Dade County still use septic tanks, and 105,000 of those are residential.

The malfunctioning of many of these septic tanks also means smelly air for residents, and as global warming-induced sea level rise continues to increase, problems are only expected to get worse in the area. According to the report, by 2040, 64 per cent of county septic tanks (more than 67,000) could experience issues every year, affecting residents and having a major environmental impact in the region.


As groundwater levels rise, low-lying areas will be impacted first, although the county has already been informed of close to 1,000 property tanks that are failing under current conditions. New regulations in the county require that the layer of dirt underneath the tank that carries out the final filtration be around 60 cm deep. This is hard to come about since there is not so much dirt between a home and the groundwater in many areas of South Florida.

Another problem is that rising groundwater levels make the soil soggy, and soggy soil is not an efficient filter for waste water. During heavy rains, high tides or elevated storm surges, the situation is even worse, as the higher flow pushes contaminated water back into residential areas.


Experts agree that the best solution would be to extend the sewer system, despite the planning time scale and investment. According to County Chief Resilience Officer James Murley: "Ripping out every septic tank and laying down pipes to connect the homes to the county's sewer system won´t be cheap." The latest price tag on doing so was a whopping US$ 3.3 billion just for private properties. Commercial properties would add an extra US$ 230 million to the bill.


Commissioner Rebeca Sosa is clear: Action is needed as fast as possible and financial assistance from the state and federal government essential. For now however, anyone who wants to connect their property to the general sewer system has to pay their own bill. The investment estimate is an average $US 15,000 per home, although in more vulnerable areas like Pinecrest the price could escalate to near $US 50,000.

For now, the report points out that beyond borrowing money to improve the situation of tanks, the county should continue to collect a per-home fee or establish special taxing districts to spread the cost among the affected neighborhoods.


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