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The $32 million North Lee County Water Treatment Plant, located in Fort Myers, Fla., is a reverse-osmosis plant with a 6 mgd capacity.
(Photo courtesy of MWH Constructors).
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Firms with water-treatment expertise combine to deliver a 6 mgd plant to Lee County Utilities in Fort Myers, Fla.
In recent years, Florida's Southwest Gulf Coast, which includes such communities as Fort Myers, Sarasota and Naples, has been one of the Sunshine State's fastest-growing regions.
"They're coming in like droves," said Patti DiPiero, public information officer with Lee County Utilities in Fort Myers. DiPiero cited the retiring baby-boomer class as well as a recent increase in the number of younger families relocating to the area.
The recently completed, $32 million, 6 mgd, reverse-osmosis North Lee County water treatment plant should represent a big step for the utility to significantly increase its capacity to deliver quality drinking water to the region.
"We knew we were going to be facing population growth issues here, and we knew we were going to need to expand capacity into the system," DiPiero said.
For design and construction of this facility, the utility used a group of contractors and engineers with expertise in this reverse-osmosis technology. These included MWH Constructors, Cape Coral, as engineer and design-build leader; Kellogg Brown & Root, Fort Myers as construction manager; civil engineer Holes, Montes & Associates, Naples; and general contractor Westra Construction Corp., Palmetto, which handled the sitework and building structures.
The Plant The new facility - like other area plants being operated by other owners - will draw water from the Lower Hawthorn Aquifer, a source of brackish water.
Ron Cass, with MWH, said the Lower Hawthorn has a total dissolved solids measure of about 2,000 - a definition of "brackish" water - and that the plant should reduce that number to about 100, and the amount of chlorides in the water to about 50.
The group of contractors started work on the job in December 2002, when the first phase of drilling the deep-injection and production wells began. The eight production wells average about 700 ft. deep, while the deep-injection wells, which help handle the resulting brine, are about 3,000 ft. deep.
Youngquist Brothers of Fort Myers installed the deep-injection wells.
Construction of the plant structure, led by Westra and overseen by MWH and KBR, followed thereafter. The facility is a mostly steel structure, with masonry exterior and metal roof.
"We combined some of the traditional Florida coastal split-faced block construction that's necessary to achieve the high windload rating, but then we blended it in with a pre-engineered building that really makes it architecturally attractive," said Cass.
Presently built to a 6-mgd capacity, the plant was designed to be easily expanded to double that, or 12 mgd. DiPiero said the utility had not finalized its schedule of when it wanted to undertake that expansion, but said, "I know they want to do it as soon as possible."
The Technology The reverse-osmosis plant will utilize a sand trap or sand separator to protect the membrane, and then cartridge filters. The facility also incorporates two two-stage membrane arrays, and a system to remove hydrogen sulfide and then treat that hydrogen sulfide air stream so it's non-odorous.
"The process is not that unique for South Florida," Cass said. "It's actually a fairly mature process now for a Floridian treatment plant. You'll see a lot more of that here compared to elsewhere in the country, because we have been more reliant on subsurface supplies."
At the same time, Cass said, the water-treatment industry has made some improvements in recent years to help provide more value to owners.
Engineers and contractors are finding ways to build facilities that are easier to expand or otherwise increase operating capacities, by as much as another 15-20 percent.
Additionally, Cass said, "We have a better modeling capability of how that TDS in the groundwater will migrate. It doesn't stay at the 2,000 TDS; over time, it goes to 2500. From the modeling, (owners can) have a better understanding of the rate at which that's going to decline, so the owner's investment will carry them through for a longer duration and therefore require less equipment replacement in the future."
Also, on the North Lee County Water Treatment Plant, Cass said the design included inter-stage boosting of the water flow, a technique used to decrease the amount of energy needed to pump the water through the system.
"With the rising cost of power, you've got to consider what it's going to cost to the municipal owner," he said.
"They are consistently under stress to maximize the benefits and minimize the investment," he added. "And when they see somebody thinking about ways to minimize their investment now and in the future, (while) giving them additional capacity, they're appreciative."
The Schedule Testing was still taking place this summer, with final completion occurring in October. DiPiero said this was about five months behind the original schedule, which dictated a May 2005 completion target.
Cass said the delay was mostly due to impacts from the hurricanes that hit Florida in 2004, amounting to about 60 days of delays to the schedule.
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