SAVANNAH, Ga. -- Machines designed to inject extra oxygen into the Savannah River to help fish breathe exceeded expectations in a two-month test run earlier this year, a federal agency said Thursday in a report that's critical to completing a $973 million deepening of the shipping channel to the Port of Savannah.
Dredging of the 27-mile (43-kilometer) stretch of river linking the fourth-busiest U.S. container port to the Atlantic Ocean has been on hold since reaching its halfway point in March 2018. That's because a court settlement required the Army Corps of Engineers to first demonstrate it could successfully offset a small loss of dissolved oxygen in the water as the river gets deepened to make room for larger cargo ships.
The Army Corps is spending $100 million to build a pair of stations on the river equipped with large machines that suck in water, swirl it with oxygen pulled from the air and inject the mixture back into the river that's home to blue crabs, striped bass and endangered shortnose sturgeon.
The agency tested the first station between March and May. Its report Thursday said the machines pumped roughly 13,300 pounds (6,070 kilograms) of oxygen into the river daily, beating its target of 12,000 pounds (5,443 kilograms). And it found that on average 95% of the extra oxygen stayed in the water instead of escaping back into the air — compared to an 80% target.
"The dissolved oxygen system is a remarkable success," Army Col. Daniel Hibner, commander of the Corps' Savannah District, said in a statement. "The weight of evidence is immense."
Dredging could resume as early as Sept. 29 now that the tests are done, said Russ Wicke, an Army Corps spokesman in Savannah.
What remains to be seen is whether the findings satisfy environmental groups and South Carolina officials who previously sued the Army Corps over the harbor expansion. South Carolina shares the river with Georgia.
Those parties argued the project would cause irreparable environmental damage. They agreed to a 2013 court settlement requiring the Army Corps to test the oxygen injectors before dredging the upstream half of the Savannah harbor. Any party that's not convinced the machines worked can scrap the settlement and return to court.
"We've always been skeptical about the use of bubblers to address the harm to the river from the deepening," said attorney Chris DeScherer of the Southern Environmental Law Center, which represents conservation groups in the lawsuit.
DeScherer has compared the oxygen injection plan to placing the river on a respirator. He said the law center will have experts evaluate the Corps' report and voluminous supporting data. The settlement gives conservation groups and other parties 30 days to respond.
Scientists tested the oxygen injectors through two full lunar cycles to account for changes in the tides, which affect how much oxygen naturally gets mixed into the river. They used dye pumped into the injection machines and 30 sensors in the water to measure how much of the extra oxygen shot into the river stayed in the water and how far it dispersed.
Wicke said the dye in some cases could be seen about 2 miles (3.2 kilometers) from the injection site. And sensors measured the amount of dissolved oxygen in the river increasing between 0.1 milligrams per liter, the minimum amount needed, to 0.68 milligrams per liter.
However, the injected oxygen failed to disperse well during the two days out of each 30-day lunar cycle when the tides caused the least amount of movement, Wicke said. He said that shortcoming should have a negligible impact on fish.
The Army Corps plans to run the oxygen injectors indefinitely, roughly from June through September each year when summer heat can cause dissolved oxygen levels in the harbor to drop below minimum standards set by Georgia and South Carolina. The agency estimates it will cost $3 million per year.