New Orleans’ water treatment plant in Algiers is no longer expected to be affected by the saltwater wedge moving up the Mississippi River.
The U.S. Army Corps of Engineers says salt levels should be within the safe-drinking threshold set by the Environmental Protection Agency when — and if — the wedge reaches New Orleans.
The change in forecast is largely thanks to two mitigation efforts: a newly raised barrier in the Mississippi is slowing the wedge. And less water is being diverted from the Mississippi into the Red River. That, coupled with recent rain in the Midwest, has increased the flow of fresh water toward the Gulf of Mexico.
“Over the past few forecasts we’ve released, the actual flows have been higher on the river, so we’ve been seeing a favorable trend,” the U.S. Army Corps of Engineers’ Matt Roe said in an interview with All Things Considered host Bob Pavlovich on Thursday.
The forecast also pushes back the wedge’s arrival at Belle Chasse and Dalcour water treatment plants in Plaquemines Parish by two weeks — to Oct. 27 and Nov. 1, respectively. Plans are in place to barge freshwater to both communities and provide Dalcour with a reverse osmosis filtration system, Roe said.
The wedge could reach St. Bernard Parish by Nov. 8, though the date is just outside the National Weather Service’s 28-day forecast for the lower Mississippi River.
Thanks to increased river flow, the wedge retreated more than five miles last week, according to the latest field measurement.
Flows have hovered at around 150,000 cubic feet per second over recent months, said Roe, and will need to double to push the wedge back out to the Gulf of Mexico.
Ron Spooner, interim head of the New Orleans Sewerage and Water Board, told city council members Tuesday that rain in the Midwest increased the Mississippi’s flow, pushing the wedge south.
“That is very good news for the entire region,” Spooner said.
The wedge of dense, salty water was at river mile 63.9 on Monday, according to the Army Corps of Engineers. It had been at river mile 69.4, about six miles south of Belle Chasse in Plaquemines Parish, on Oct. 2.
Despite the retreat, Roe said the wedge is forecast to resume its northward creep. Its toe could eventually reach river mile 103, near New Orleans’ Carrollton water treatment plant, past its Algiers facility. Salinity levels at the toe of the wedge remain low, with high-salinity water trailing 15 to 20 miles behind.
While the level of salt in the water that’s expected to reach Algiers should be far below the safe-drinking threshold, it will be higher than usual. The Sewerage and Water Board said in a statement Thursday that it plans to dilute the salt water with added fresh water before it’s treated. Salt levels at the Carrollton plant are expected to stay within typical levels.
The Sewerage and Water Board is still moving forward with plans to build a pipeline to bring fresh water from north of Kenner to the Carrollton plant, if needed. Construction hasn’t started yet, while in Jefferson Parish, part of its temporary line is already laid.
Spooner told council members Tuesday that earlier cost estimates for New Orleans’ pipeline had been revised upward. The cost is believed to be close to $300 million, though it could come down now that the city no longer has to build it quickly.
Councilmember Joseph Giarrusso said at the meeting that some of the funding should come from the federal government — and pointed to reporting from The Times Picayune | The New Orleans Advocate that the Army Corps of Engineers knew that its dredging of the lower Mississippi to facilitate shipping commerce would make saltwater intrusion worse.
He described the four parishes affected by the wedge as the country’s “sacrificial lambs.”
“I think it is completely warranted to expect our federal partners to help contribute,” he said, “given what our sacrifice means for the rest of the nation.”
