City officials are looking at investing up to an estimated $22.5 million (S$30.3 million) to build “deep injection wells” to serve as a third mechanism for managing wastewater.
Officials discussed the proposed plan during the City Commission’s Dec. 10 work session.
Officials said deep injection wells that would be dug 800 to 1,200 feet underground would serve as a “third prong” in the city’s system to handle water overflow emergencies such as the estimated 18 inches of rain dropped by Hurricane Hermine in August 2017.
The hurricane prompted the city to find an additional tool to handle wastewater reclamation overflow.
However, some officials voiced concerns as to whether the proposed deep well system fully addresses Largo’s wastewater overflow problem, or whether it poses potential leakage into the city’s source of drinking water.
Largo’s wastewater reclamation facility currently discharges treated effluent to Tampa Bay through Feather Sound, which is its only discharge method other than reclaimed water.
Largo currently has no backup discharge system in a flood emergency such as a hurricane or a failure in its current discharge system to Feather Sound.
The city discharges between eight and 15 million gallons of treated wastewater daily into Feather Sound that leads out to Old Tampa Bay.
In the wake of Hurricane Hermine, the city in August 2017 hired Tampa-based aquifer storage recovery and geological consulting firm ASRus to conduct a feasibility study that outlines four alternatives to help handle the city’s effluent discharge.
The Florida Department of Environmental Protection reviewed the ASRus study this year and deemed its three surface water alternatives “not viable,” since FDEP no longer issued surface water discharge permits in Pinellas County.
ASRus’ deep injection well plan calls for the discharge of the city’s treated wastewater in a well 800-1,200 feet underground in a permeable zone well below the city’s aquifer for drinking water.
Largo Engineering Services Director Jerald Woloszynski and Environmental Services Assistant Director Shelby Beauchemin outlined the ASRus plan that recommends the city initially install two deep water wells with a third well to be installed at a future date.
Two of the proposed three wells would be at the city’s Wastewater Reclamation Facility site with a third to be located offsite. A third well and storage tank offsite would provide additional effluent discharge capacity, according to the study.
The estimated cost for building two wells: $22.5 million (S$30.3 million) for design and construction. One deep water well would cost $13.5 million (S$18.2 million), which includes $3.5 million (S$4.7 million) to design and $10 million (S$13.5 million) in construction costs.
The wells would help handle the city’s 18 million gallons daily of permitted average daily wastewater flow.
A third well could be added in the future should the first two wells not be sufficient, according to the ASRus study.
The wells would have an estimated 50-year lifespan that would also require an estimated $100,000 in annual maintenance, according to the survey.
Woloszynski recommended the city build two wells.
He said deep injection wells are “highly endorsed” by the FDEP.
“It’s unfunded, but it would be a cost avoidance if we did build the two deep well injection projects,” he said.
The deep wells would supplement the city’s water reclamation facility, and secondary overflow wastewater reclamation storage tank constructed in 2018.
“It would be the third way for us to dispose of our water,” Woloszynski said.
Other municipalities employing deep water injection wells include Tarpon Springs, Oldsmar, St. Petersburg and Hillsborough County, Woloszynski said.
“This is a proactive approach vs. a reactive approach,” Woloszynski said. “It brings the third prong in our ability to discharge surface water in Old Tampa Bay.”
ASRus chief executive Mark McNeal, who has served as a city consultant, said deep injection wells would provide “a safe tool in your toolbox.”
However, Mayor Woody Brown voiced reservations about the plan, including concerns to whether deep wells could potentially leak into the city’s aquifer.
“On the surface, it doesn’t sound like a great idea to me,” Brown said. “It looks like we’re trying to fix a leaky system, rather than the elimination of rainwater when it rains during high flow events.”
Brown said that while he is willing to review it, “it is hard for me to justify injecting our wastewater into the ground.”
Other commission members said they wanted to review additional information about alternative methods for managing the city’s potential wastewater overflow before moving forward.
Commissioner Michael Smith questioned city officials whether there was another feasible alternative to deep injection wells.
“This doesn’t feel like thinking outside the box to me, to think of a different way of doing something,” Smith said.
McNeal said a state study reported that deep injection wells employed by municipalities have so far operated flawlessly.
Woloszynski said the discussion will continue.
At a future work session, Woloszynski said staff intend to put together a panel of independent experts in the fields of nutrient loading in Tampa Bay and aquifer protection.