Nearly 40 square miles of North Cape Coral is sinking, an inch or more every year, due to over-pumping the aquifers below the city for household water.
The reason for a deepening depression in that area was detailed in a recent study in the journal Science of Remote Sensing by researchers from the Geological Survey of Norway.
At the center of the sinking soil is Cape Coral’s desalinization plant and the 22 wells scattered through the surrounding neighborhoods. Pumping brackish water from as deep as 1,250 feet into the reverse osmosis plant,the wells produce more than one million gallons of clean, drinkable water every day for the city’s burgeoning population.
But that rate of extraction comes with serious environmental costs that far exceed the price paid in dollars to run the desalinization plant, the researchers say.
The heavy pumping lowers the water table by more than three feet of water per year, and without giving the aquifers time to refill, so much underground space that held water has collapsed it could house enough water to fill eight Empire State Buildings.
Now that the aquifer has compacted it can never refill. The landscape above is sinking into the void, which has dropped the ground level surrounding the desalinization plant by as much as 1.5 feet in a process called subsidence, the Norwegian researchers report.
The oblong-shaped depression is poised to wreak havoc on anything built on the land surrounding the water plant, which includes hundreds of homes, several high schools, two middle schools, two parks, two sports complexes, and a hospital.
“Groundwater pumping for feeding the … desalination facilities is the primary factor responsible for land subsidence in the northern part of the city,” the study's authors wrote. “Such deformation likely results from overusing the aquifer system. That aggressive groundwater pumping might potentially facilitate natural sinkhole formation.”
No scientific agreement
Rachael Rotz, a hydrogeologist at The Water School at the Florida Gulf Coast University, was not involved in the study, but said the subsidence around the northern wellfield could be a mere coincidence. The real culprit, she said, could be growth.
"Cape Coral is undergoing a huge population explosion," she said. "The study didn't really look at how the development, building new houses, and filling in wetlands as well as increased irrigation for landscaping and potentially agriculture could be contributing to the ground sinking."
Rotz also said since the city draws its water from more than 1,000 feet below the surface it’s highly unlikely over-pumping is to blame for the surface subsidence.
"It's a bit of a stretch to think that water pumping from so far down could be creating that much stress," Rotz said. "I think we need to be very careful before we start pointing fingers at the source of these problems until we can do a more thorough examination."
Whatever the reason for the 40-mile oval of subsidence in North Cape Coral, there is little disagreement that sinking land could cause structural issues to develop in some of the many homes, schools, and businesses in the region.
Water table dropping
Land subsidence is an often-overlooked environmental consequence of the way land-use and water-pumping practices are designed.
Florida leads the nation in the use of desalination technology to treat brackish water and seawater with more than 130 desalination plants. More than 80% are concentrated in the coastal areas of central and south Florida.
Two are in Cape Coral. The city was the first municipality in the United States to use the reverse osmosis process on a large scale in 1977.
With upgrades over the next eight years, the city had the largest low-pressure reverse osmosis plant in the world, capable of producing 15 million gallons of fresh water per day.
The northern desalinization plant started operating in 2010. Coupled with the first plant in the south, the city can produce about 30 million gallons per day, meeting Cape Coral's drinking water needs.
But ever since the northern well came online the groundwater level has dropped at a pace of more than three feet per year, the Norwegian researchers report. So much water is being pumped out of the vast underground reserves that the water table is 40 feet lower than it was.
The Norway researchers discovered the most severe subsidence is happening at a rate of 1.26 inches per year, matching up exactly with where the wells for the northern plant extract water from the ground.
WGCU provided Melissa Mickey, Cape Coral’s communications manager, with a copy of the journal of Science of Remote Sensing’s article and asked her for comment on its findings.
Mickey deferred questions to Cape Coral Mayor John Gunter.
WGCU also provided the mayor with a copy of the study via email and requested an interview several times. Gunter did not reply.
A global pattern
The U.S. Geological Survey reports that more than 17,000 square miles in 45 states have been directly affected by subsidence, and 80% of that is due to the exploitation of underground water. It will only get worse with more development, which will exacerbate existing land-subsidence problems and initiate new ones, the agency found.
Florida’s water managers are confident that the state’s residents will have their drinking water needs met in the foreseeable future. But in the long-term, the National Resources Defense Council says Florida is one of 14 states with an extreme or high risk of running out of enough water as demand exceeds sustainable supply by 2050.
The Norwegian study on Cape Coral's over-pumping and land subsidence does not blame anyone. It does, however, raise questions about the wisdom of current water extraction practices and the need for better overall management of water resources to prevent further environmental impacts.
“This understanding is vital not only for Cape Coral but for any region facing similar challenges,” the authors wrote. And “reinforcing the importance of sustainable practices in resource management on a global scale.”
The study compared Cape Coral’s situation with other places worldwide, such as Turkey, China, and Mexico City. In these areas, ground subsidence has been observed under similar circumstances — mainly due to the removal of large amounts of groundwater.
This comparison is crucial as it shows that Cape Coral's situation is not unique, but is part of a global pattern of environmental change driven by human activity.
“In this paper, we delve into an intriguing issue faced by Cape Coral, Florida, where the ground is gradually sinking, a phenomenon deeply connected to the methods used for obtaining fresh water in the region,” the authors wrote.
“This study is significant as it not only highlights a local environmental challenge but also draws parallels with similar global instances, enhancing our understanding of the broader implications of groundwater extraction.”
Environmental reporting for WGCU is funded in part by VoLo Foundation, a non-profit with a mission to accelerate change and global impact by supporting science-based climate solutions, enhancing education, and improving health.
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