News

By Ann Henson Feltgen
    
Saltwater intrusion leading to contaminated drinking water wells has long been feared in South Florida.
    Billions of dollars have been spent on measures to protect our water supply — mostly paid for by utilities and their customers — and have paid off, so far.
    The invisible underground barrier separating salt and fresh water is holding salt water back to the 1995 boundary or even farther east, scientists say.
    “This is a success,” said U.S. Geological Survey hydrologist Scott Prinos, who helps monitor saltwater intrusion in several South Florida counties. “The question is: As we move into the future and with population increases, will these measures continue to be effective?”
    The barrier between fresh and salt water — called the saltwater interface — preserves the pristine water in the 3,000-square-mile Biscayne Aquifer, which supplies potable water to about 5.8 million residents in South Florida and the Florida Keys.
    The struggle to forestall saltwater intrusion began in the 1930s when canals were dredged to drain the Everglades, Prinos said. As water levels declined in the spongy aquifer, salt water — which is heavier than fresh water — began to flow inland. Population pressure, drought and higher sea levels all play a part in interface movement. Although the interface is stable, it imperceptibly ebbs and flows seasonally.
    Florida receives an average of 54 inches of rainfall per year, much of which seeps into the ground and refills the aquifers. This year’s rainy season officially began May 10 with South Florida in a severe drought that extended through July. The August and September rainfall helped, but the area was still technically in a drought.
    The remainder of the season is expected to have above average rainfall due to the effects of an El Niño, according to the National Oceanic and Atmospheric Administration.
    The South Florida Water Management District, which governs potable water for South Florida, has for years been nudging municipalities to control their water usage by adopting conservation measures, installing reverse osmosis plants that can convert the brackish water from the deep Floridan Aquifer into drinking water and storing water during the rainy season for use in dry periods. Last year, these conservation measures were mandated by state law.
    Previously, the carrot at the end of the water district’s stick was a water use permit that allows specific withdrawal amounts from the Biscayne Aquifer for up to 20 years. Now South Florida communities and counties are spending billions of dollars to adopt the latest technology and build new facilities, passing along the cost to residents and businesses in increased fees.
    For its part, the water district has been upgrading and monitoring water control structures that also retard saltwater intrusion, said Pete Kwiatkowski, a SFWMD hydrologist and manager of the resource evaluation section.
    The agency also provides substantial grants to cities, special districts and utilities for these projects. The agency issues a request for proposals, then reviews the projects based on a list of criteria and available funding. The projects must be considered nontraditional, such as aquifer storage and recovery, reverse osmosis plants and reclaimed wastewater used for irrigation. Since 1997, the agency has approved $1.4 billion in funding for 488 projects.

Local efforts
    Because the elevation of Palm Beach County is much higher than counties farther south, the advance of saltwater intrusion is less. But efforts are underway by Palm Beach County cities and range from taking less water out of the Biscayne Aquifer and more water from the Floridan Aquifer, rotating well usage, using water storage, reclaiming water for irrigation to eliminating withdrawals from the aquifer entirely.
    Boca Raton, the second- largest city in Palm Beach County, stores water by back pumping excess runoff into canals, where the water percolates into the ground and the Biscayne Aquifer for use during the dry season. The city also maintains canal levels at a fixed rate to keep salt water from intruding. The city uses reclaimed water for irrigation.
    Boynton Beach officials learned five years ago that saltwater intrusion may become a problem for some of the city’s wells east of Interstate 95, so they reduced usage of those wells from 16 million gallons per day to 5 million gallons per day. Boynton Beach provides water to Ocean Ridge and Briny Breezes.
    Delray Beach city commissioners on Sept. 3 approved a study to look at alternative water supplies and methods to meet the city’s demand. The study will look at using deeper wells and different treatment. A new plant would be included in the plan. The city has hired a firm to weigh the alternatives and costs.
    Highland Beach taps the Floridan Aquifer and a reverse osmosis plant desalinates up to 3 million gallons of water per day. The city uses maybe half of that even during the winter season. Because the town taps into the deeper aquifer and uses desalination, Highland Beach residents are not subject to water restrictions.  
    Lantana operates 10 wells scattered throughout the town and provides water to 3,300 customers. The town’s water supply, which comes from the Biscayne Aquifer, is adequate and growth will not crimp the supply.   
    Manalapan’s wells are all on the west side of U.S. 1 and have not had a problem with saltwater intrusion. The town operates six wells, two of which tap into the Floridan Aquifer and require reverse osmosis to take out the salt water. Manalapan is in discussions with Boynton Beach about taking over Manalapan’s water plant.
    West Palm Beach silenced its wells that tapped into the Biscayne Aquifer in 2012 and the city began relying on groundwater. The water utility does not face saltwater intrusion or worry about sea level rise, and the supply is a renewable resource. West Palm Beach provides water to the town of Palm Beach and to South Palm Beach.

The future
    Much has been said about the effects of climate change and what it may mean for South Florida’s potable water supply.
    “It’s too early to declare a victory over saltwater intrusion,” said Eric Draper, executive director of Audubon Florida, which supports and stresses conservation of natural resources, including water.     “Saltwater intrusion is also a matter of sea level rise, and we don’t know what will happen. As sea levels rise, it puts more pressure to move the salt water that’s underground. I don’t know if we have studied that yet.”
    Scientists agree that climate change is a factor, but say efforts are taking place to save the aquifer and, as technology continues to advance, more strategies will come into play.
    USGS’s Prinos said South Florida governments are working together to identify areas of concern and come up with proactive solutions.
    “We maintain salinity control structures, relocate wells that are very close to the coast farther west, we are using [best] practices with water conservation and some cities are using reclaimed water for irrigation,” he said.
    Prinos added that technology now allows pinpointing where the saltwater interface is and whether it is moving east or west.
During mapping in 2011, the agency deployed helicopters equipped with electromagnetic technology that can precisely determine where the interface is located. Formerly, the salinity in sentinel wells along either side of the interface was used to determine if salt water was moving.
    “In some cases, we had the front farther west than it really was,” Prinos said.
    “As we move into the future, we will continue to be vigilant, watching and considering ways to hold it back.”