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Swiftmud says up to 1.8-billion gallons could be stored under Largo and Clearwater.
By CHRISTINA HEADRICK
© St. Petersburg Times, published October 8, 2001
Imagine six Tropicana Fields full of treated wastewater used to water lawns. That's how much storage space engineers estimate the cities of Clearwater and Largo may need to significantly expand their reclaimed water systems.
With that in mind, the cities are considering a $9.5-million project to pump the reclaimed water underground.
As much as 1.8-billion gallons of reclaimed water may someday be pumped and stored under the cities each year under a proposal brought to the cities by the Southwest Florida Water Management District, or Swiftmud.
The process is called aquifer storage and recovery, and areas on Florida's west coast are leading the way nationally in the development of the technology, say experts in the field.
In southwest Florida, a dozen such reclaimed water storage projects are in various stages of study or permitting, while at least another half-dozen governments have begun to explore the technology, said Mark McNeal, a hydrogeologist at CH2M Hill, a Tampa consulting and engineering firm that has worked on most of the ongoing projects.
One of the first such projects in America is being tested in northwest Hillsborough County, McNeal said. Englewood, in Charlotte County, is not far behind in testing its new underground storage system.
Meanwhile, St. Petersburg has almost completed its first reclaimed water storage well and is getting ready to begin testing the $800,000 project this year, said Ralph Craig, St. Petersburg's hydrogeologist.
The Clearwater and Largo projects would be a bit different from the others. In addition to building their own systems, Swiftmud would like to extend a pipeline from the cities to Pasco County.
During the rainy season, excess reclaimed water from cities would be pumped over drying wetlands in Pasco, which are near the well fields that supply much of the region's drinking water.
Pinellas County officials opposed a more expensive, expansive proposal for such a project five years ago, citing health concerns about mingling reclaimed water with drinking water supplies.
Nevertheless, Clearwater commissioners recently approved working with Swiftmud and Largo to do a $150,000 preliminary study of the concept.
Largo officials are still debating whether they want to chip in $50,000 toward the deal, mainly because of concerns about the costs and benefits of such a proposal, said Norton Craig, the city's environmental services director.
Aquifer storage and recovery is not a new idea. At least 40 systems exist in the country, McNeal said, and there are at least 60 more in development. Most of the systems, however, have been created to store drinking water.
Engineers have seen a need to apply the technique to reclaimed water, too, particularly on the west coast of Florida, where reclaimed water systems are the most developed in the state. As they have expanded, the systems are running out of the water they promise to provide people who hook up, McNeal said.
The problem is that the supply of reclaimed water fluctuates as the weather changes, said Andy Neff, Clearwater's public utilities director.
During the rainy months of the year, extra water flows into the city's sewage system, and fewer people water their lawns, so the city has millions of gallons of excess wastewater, which flows into local waterways, Neff said.
During the dry season, however, more people are watering their lawns and less water is flowing into the city's sewer plants, where it can be cleansed and turned into reclaimed water. As cities expand their systems, there could be a reclaimed water crunch, Neff said, forcing restrictions on the days the water can be used.
Consultants have estimated that because of the shortage of water in the dry season, only six or seven Clearwater neighborhoods can be hooked into Clearwater's reclaimed water system -- unless the city finds some way to store as many as 1-billion gallons of treated wastewater for use during the dry months, Neff said.
Similarly, Largo has about 1,600 reclaimed water customers and is almost maxed out during May and June on the reclaimed water it can supply.
St. Petersburg, which has the oldest and largest urban reclaimed water system in the country, has run out of reclaimed water at times during dry months, with roughly one-tenth of its potential customers watering their lawns, officials there say.
To understand how aquifer storage and recovery, or ASR, works, it helps to sit down in Ralph Craig's office in St. Petersburg's city utility complex and imagine taking a trip hundreds of feet underground.
Craig, a hydrogeologist, has large diagrams he uses to explain how the city plans to store more than 100-million gallons of reclaimed water between confining layers of limestone about 500 to 600 feet below the ground.
Then Craig pulls out his long plastic boxes of rocks and clay. These are samples that were taken every 5 feet as the city dug its first aquifer storage well.
For the first 95 feet of the digging, the boxes contain samples of brown sand, alabaster fragments of shells and greenish-brown clay. Then there is chalky white limestone and finally harder rock about 195 feet down. At 300 to 400 feet, the samples are of a hard, solid limestone.
Then around 500 feet, the limestone suddenly looks porous with many fine holes, like a sponge. There are samples of gooey, pale green mud. This is the area, filled with brackish water, where St. Petersburg plans to pump treated wastewater to store it until it is needed again.
When freshwater is pumped into such a layer, says McNeal, it radiates up to 1,000 feet from the well, perhaps the size of a city block. Because the wastewater is cleansed to meet drinking water standards before it is pumped underground, it isn't treated again when it's retrieved.
Generally, reclaimed water storage wells are located away from wells that pump drinking water, McNeal said, avoiding any concerns about mingling the sources of water.
That could be a concern in Clearwater, which unlike Largo or St. Petersburg has a system of wells that supply one-fifth of the city's drinking water. And Clearwater intends to boost the wells' production of drinking water.
"We need assurances there's no impact to our drinking water supply with an ASR project," Neff said. "That's why we need a feasibility study."
Anthony Andrade, a conservation analyst with Swiftmud, said that even if reclaimed water somehow mingled with drinking water, it would still be safe because reclaimed water is treated to meet drinking water standards.
"This is a very safe technology," he said.