The addition of Aquifer Storage and Recovery (ASR) wells could add more flexibility to the management of Lake Okeechobee, according to David Pyne, president of ASR Systems in Gainesville.
Pyne spoke to the Florida Senate Committee on Environment and Natural Resources on March 2, in support of Senate Bill 94, which promotes the use of ASR wells in the Lake Okeechobee Watershed Restoration Project (LOWRP).
In a March 8, telephone interview with the Lake Okeechobee News, Pyne said the 80 ASRs planned in LOWRP could store 448,000 acre feet of water – the equivalent of about one foot of water on Lake Okeechobee – each year. He said ASR does not have the same limits as above ground storage. When the area experiences back-to-back wet years, they could continue to store more water underground in the aquifer.
When ASRs were initially considered as part of the Comprehensive Everglades Restoration Plan (CERP), modeling only looked at using the ASRs when the lake was already high, he said. But ASRs do not move water quickly. Instead, he explained, ASRs could be used to store water year round, except during extreme dry periods when the ASR wells would be pumping water back to the surface to supplement water supply.
Storing that extra water would mean the U.S. Army Corps of Engineers and the South Florida Water Management District (SFWMD) would have another tool to manage the flow of water. “There's a lot of opportunity to store a lot of water and a lot of opportunity to recover a lot of water,” he said. “There really is no limit on the ability to store water underground.”
Pyne said the initial ASR study only looked at storing water in the Upper Florida Aquifer while new studies show they can store more water in the Middle Floridan Aquifer, now more commonly called the Avon Park Permeable Zone. The current plan calls for constructing the ASR wells in pairs, with one in the Upper Floridan Aquifer (UFA) and an adjacent one in the Avon Park Permeable Zone (APPZ).
"There is good reason to believe that the APPZ wells will accept and yield water at higher flow rates than 5 MGD, but at this point it is wise to be on the conservative side.," he explained. While the current plan for LOWRP is limited to 80 ASR wells, "we are not limited to 80 ASR wells," he added.
“When we get the first round of eight to 10 ASR wells in, we will have a better handle on it,” said Pyne.
If the 80 ASR wells had been in operation a year ago, approximately 448,000 acre feet of water could have been be in the aquifer instead of in the lake. Had that been possible, the lake would be a foot lower now and the lake would not be in the position that requires freshwater releases to the St. Lucie Estuary.
After several years of pumping treated freshwater into the ASRs, water managers should also feel more comfortable they have that reserve to meet water supply needs in dry years. This would allow them to give the Caloosahatchee River the optimum 1,000 cubic feet per second (cfs) freshwater flow the estuary needs in the dry season instead of cutting it back to the minimum 450 cfs when there are concerns about water supply.
Adding ASRs would give water managers another tool to restore the historic water flows, Pyne said.
Before flood control, water sheetflowed very slowly into the lake. According to the U.S. Geological Survey, before the flood control canals were dug to drain the area from Orlando to Lake Okeechobee for development, water that fell at the top of the system took six months to sheetflow into the lake. Now it takes just a few weeks for water that falls near Shingle Creek to flow to the big lake.
ASRs are NOT deep injection wells
Pyne said while deep injection wells (DIW) could also play a part in reducing harmful discharges to the coastal estuaries, ASRs and DIW are two different things.
ASR pumps water that has been treated to drinking water standards into the Upper Florida Aquifer or the Avon Park Permeable Zone. This clean water forms a freshwater bubble. Water can later be extracted from that bubble as needed.
DIW wells go much deeper, pumping water into the Boulder Zone, as much as 3,500 feet deep. The Boulder Zone connects with the ocean miles out to sea. Water pumped into the Boulder Zone cannot be recovered. In Florida, deep injection wells have been used since the 1960s to dispose of municipal wastewater. In the vast Boulder Zone, the wastewater mixes with salt water. Pyne said water in the Boulder Zones moves very slowly – so slowly that computer models indicate it may take 400 years for it to reach the Straits of Florida.
No one actually knows how long it will take water pumped into DIWs to come out in the ocean because it's all based on computer modeling, he said.
Pyne said adding ASRs to the CERP projects already planned or under construction south, east and west of the lake could reduce the need for harmful freshwater discharges to the coastal estuaries by 80 percent. The addition of DIWs could get that number to 90% or 100%, he added.
DIWs – at one time described by water managers as potential “estuary protection wells” – could be used in extreme high water years to prevent harmful discharges to the coastal estuaries. DIWs, which can pump water at 10-20 million gallons a day, have much higher flow potential than ASRs, which have a capacity of about 5 million gallons per day. Another time saver: Water pumped it DIWs does not have to be treated to drinking water standards first.
While most of the time, the goal is to use ASRs and reservoirs to store water, water managers need faster solutions to move water when the deer in the Everglades are drowning. “When you’ve got two back-to-back hurricanes crossing Lake Okeechobee with just a few weeks,” having the capacity to quickly move that water into DIWs could save people and wildlife from flooding without destroying the salinity balance in the estuaries, he explained.