Could deep wells reduce discharges to estuaries?

OKEECHOBEE — Could Deep Well Injection (DWI) be part of the solution to reducing harmful freshwater discharges to the coastal estuaries?

While the Lake Okeechobee Watershed Restoration Project plan no longer includes DWI, the South Florida Water Management District has put the idea back in play.

At the June 23 LOWRP meeting, Lisa Aley of the U.S. Army Corps of Engineers said DIW was removed from consideration as part of the restoration.

DWI was not a component in the 1999 Comprehensive Everglades Restoration Plan (CERP), she explained.

In order to evaluation the potential effects of DWI within CERP and its potential effects on other CERP projects, a comprehensive regional analysis needs to be performed, Aley explained. The comprehensive regional analysis cannot be undertaken within the constraints of the LOWRP scope, schedule or budget to meet the corps’ planning milestones, she added.

For these reasons as well as the need to understand how DWI may perform within the context of ecosystem restoration, the corps screened DWI from further consideration within LOWRP, she stated.

The primary issue brought up by those who oppose DWI is that the water is lost when it is injected into the boulder zone and this freshwater cannot be recovered. In effect, DWI sends the water to tide.

Aquifer Storage and Recovery (ASR) wells inject water into the Floridan Aquifer. About 70 percent of the water injected into the upper Floridan Aquifer can be recovered for use during drought.

Proponents of DWI say the deep wells would be used only in emergencies to prevent harmful discharges to the coastal estuaries.

Why not use only ASR wells? There is a limit on how much water can be injected into the Florida Aquifer, according to the report given at the LOWRP meeting.

In addition, in times of excess rainfall, water can be injected via DWI into the boulder zone at a much faster rate than water can be injected into ASRs.

At the Water Resources Advisory Commission (WRAC) meeting Feb. 2, Robert Verrastro, lead hydrologist, explained that roughly a billion gallons of water a day could be injected into the boulder zone without affecting the ASR wells.

The boulder zone is around 3,000 feet underground.

Water pumped into deep injection wells cannot be recovered. The water in that zone is salt water. The boulder zone is filled with seawater and connects with the ocean many miles offshore, according to the presentation at the WRAC meeting.

Boulder zone injection wells have a simple design, would require no additional land acquisition and can hold relatively high capacities compared with ASR wells. The deep wells could be built in advance of large reservoirs, and could assist in estuary and dike protection.

Boulder zone wells can inject 30 cubic feet of water per second (cfs), compared with about 8 cfs for ASR.

The disadvantage is that the water is lost, as though it had been sent to tide.

This technology is not new. There are 180 deep injection wells in operation in Florida today. Most of these wells are used for wastewater disposal.

While LOWRP is not considering DWI, the SFWMD Governing Board is researching the idea.

“Deep injection wells provide yet another option for reducing excess stormwater during high-water events, when no amount of storage could completely prevent harmful releases to the estuaries,” said SFWMD Governing Board Vice Chairman Jim Moran, at the board’s June meeting. “The operation of deep injection wells would be specific to address only extreme types of situations. As future restoration projects come online, deep injection wells will receive the modifications necessary to increase their functionality in an ever-changing water management landscape.”

A report is scheduled for presentation to the SFWMD board at its regular public meeting in September.

DWI boulder zone

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