TAMPA — With a backdrop of rising seas in Florida that in 80 years could be 3 feet higher than now, the owners of the sea-level-situated desalination plant in Apollo Beach have embarked on a multiyear study to determine how to avoid the potential swamping of the $158 million plant that changes saltwater into water people can drink.
The 15-year-old plant, which began amid a controversy of construction and design cost overruns, supplements the 157 million gallons of water a day provided by Tampa Bay Water, the wholesale dealer of potable water in the region. It’s been offline since January, but now is beginning to crank up its process of pulling saltwater in one end and spewing freshwater out the other.
There may come a time when water from the plant will be a year-round key component to slaking the thirsts and sprinkling the lawns of Tampa Bay area residents, and that could be around the time when the rising sea levels become the plant’s biggest threat.
The plant is right at sea level, which is expected to rise 6 inches or more over the next couple of decades as global warming melts the polar ice caps.
“In terms of the physical location of the plant versus sea-level rise,” said Alison Adams, chief technical officer with Tampa Bay Water, “we are beginning a process — an asset management program — to determine what infrastructures will be vulnerable to rising seas and storm surge.”
The agency is part of a climate science advisory committee, which is looking at all its infrastructures and how they will be affected by sea-level rise and other climate change threats. The assessment is not yet completed.
“It’s a process that takes a couple of years,” Adams said.
The plant does not push out freshwater all the time. Among the reasons: It’s expensive to do that and Tampa Bay Water has been judicious about cranking it up when other, cheaper sources of water — the Floridan aquifer and the 15.5 billion gallon C.W. Bill Young Regional Reservoir — are readily available.
The water that comes from the desalination plant is twice as expensive as the water drawn from the massive reservoir and four times as expensive as water that is pumped from the aquifer.
Those sources provide abundant water during the rainy season, but when it turns dry, like now, the desalination plant kicks into gear.
“We brought it up over the past couple of weeks,” said Adams. “We’re in the start-up process, pushing out about 12 million gallons a day. We will increase that over the next week or so to 16 million gallons and run it through the end of the dry season, probably through May.”
Its production capacity is 25 million gallons a day and provides water to public utilities in Hillsborough, Pinellas and Pasco counties and the cities of Tampa, St. Petersburg and New Port Richey, which in turn sell it to residents.
The desalination plant’s life expectancy is about 40 years, Adams said. At that point, rising seas may threaten the structure, which is located next to the TECO Big Bend power producing complex along the southern shore of Tampa Bay.
Besides sea levels rising, climate change also may impact rainfall in Florida, an integral — and unpredictable — piece of the water-supply machinery.
“It’s never too soon to talk about shifting rainfall patterns,” said Adams. “We’re working with the University of Florida and Florida State University researching potential changes in rainfall patterns.
“Changing patterns will have a direct impact on surface water withdrawals,” she said, and that could push the agency into round-the-clock use of the desalination plant, which now runs an average of 237 days a year.
Tampa Bay Water has contracted with American Water-Acciona to run the plant for $6.2 million a year. That pays for the production of water, having the plant ready to produce water at any time, and the upkeep of the facility, with 23 full-time employees.
“There are a lot of maintenance activities, a lot because it’s a desalination plant,” Adams said. “They always have a full crew there.”
The plant runs even when it is not producing potable water, circulating saltwater through the system to keep wet the membranes that are key in the desalination process.
This past wet winter meant the other water sources were abundant, Adams said. Because of the higher-than-normal winter rains, rivers flowed and the reservoir brimmed.
But rainfall, about 52 inches a year in Tampa, may change in the decades to come.
“In the climate model projections, there is a wide range in the rainfall predicted and none of it is definitive,” Adams said. “We’re closely watching it from year to year to see if there are any changes in rainfall.”
And some summer rainfall pattern changes already have taken place, she said.
“The way it arrives is different,” she said. “It’s not the volume, but the timing. Now, we’re getting series of heavy rains over three to four days and then no rain for weeks.” Becoming less frequent are the daily afternoon thundershowers in July, August and September.
“We are noticing it happening right now,” she said, “and we will continue to watch and evaluate the changing rainfall patterns.”
As the region grows and the climate remains an uncertainty, the need for more water sources is imperative, Adams said.
Agency projections say that though it may be two decades before new sources will be needed, preliminary plans call for a second desalination plant on the Gulf of Mexico, probably near the mouth of the Anclote River in Pasco County.
“The next source of water will not be inexpensive,” she said. “We’ve tapped out all of those.”