Wondering what will happen when water pumped into deep injection wells comes out in the ocean? You’ll have to wait millions of years to find out.
Deep injection wells (DIW) are the source of much misinformation and confusion, according to South Florida Water Management District Lead Hydrologist Bob Verrastro.
Most recently, the use of DIW was in the news when Manatee County Commissioners authorized a deep well injection project at the former Piney Point phosphate processing plant to prevent future releases of wastewater from that plant into Tampa Bay.
There are more than 180 DIWs in use across Florida, according to the Florida Department of Environmental Project. Most are used to dispose of excess wastewater, especially in the rainy season when it is difficult to recycle water on sprayfields or use it for irrigation because the ground is already saturated by rainfall.
In Florida, DIW have been used since the 1960s to dispose of municipal wastewater and landfill leachate. The EPA classifies municipal waste disposal DIWs are Class I.
The EPA permits six classes of DIW:
• Class I – industrial and municipal waste disposal wells;
• Class II – oil and gas related injection wells;
• Class III – solution mining wells;
• Class IV – shallow hazardous and radioactive waste injection wells
• Class V – wells that inject non-hazardous fluids into or above underground sources of drinking water; and,
• Class VI – geologic sequestration wells.
Deep injection wells (DIW) inject wastewater around 3,000 feet down into the Boulder Zone, explained Verrastro.
The Boulder Zone has large voids which contain salt water from the ocean. Water sampled from the Boulder Zone is 20,000 to 30,000 years old, he explained, based on isotopic analysis on water sampled by the U.S. Geological Survey.
Water from the Boulder Zone “flows” to the ocean, very, very slowly. The movement is so slow it is hard to detect. It travels less than 1 foot every 100 years, the hydrologist explained.
Let’s do the math. One mile is 5,280 feet. So it would take more than half a million years for that water to travel one mile. For example, the deep injection well used by the Okeechobee Utility Authority to dispose of excess waste water in the wet season is about 40 miles from the coast, so it would take that water more than 20 million years just to reach the coast. The Boulder Zone water does not come out at the shoreline. It is estimated to come out miles offshore, so add a few more million years to the total.
Of course, because the water moves so slowly, no one knows exactly where the water will come out in the ocean. They can’t test their theories. DIW has been used in Florida since the 1960s, and that’s not long enough for the water to move even 1 foot.
For years, Newton Cook of United Waterfowlers-Florida, has suggested using DIW technology to get rid of the tons of muck on the bottom of the center of Lake Okeechobee.
Verrastro does not support that idea for cleaning up the Big O. He said a slurry of muck would clog a DIW.