The saltwater wedge slowly creeping up the Mississippi River is no longer threatening drinking water for Louisiana’s biggest metro area — but officials in Orleans and Jefferson parishes are moving forward with mitigation plans, in case forecasts shift yet again.
Jefferson Parish has installed and completed testing on a pipeline intended to pull in fresh water from upstream to dilute any briny water that might make its way into the drinking water supply, while Orleans Parish has identified a contractor for similar work at its Algiers water plant.
The problem that led to those preparations has been looming for months, as drought conditions up and down the Mississippi led to low flows, which allowed dense salt water from the Gulf of Mexico to creep northward along the river bottom, contaminating drinking water in Plaquemines Parish and threatening communities farther upriver.
Forecasts initially estimated that the salt water would reach New Orleans in October, causing a scramble to build infrastructure to mitigate the threat. But the latest forecast from the U.S. Army Corps of Engineers predicts that no communities beyond Dalcour are likely to be affected.
After receding about five miles downstream earlier this month, the saltwater wedge resumed its slow creep upriver this week, with the front of the wedge reaching river mile 65.8, about 30 river miles below the Algiers water treatment plant, which serves the southern part of New Orleans.
Jefferson Parish has laid 15 miles of flexible pipeline along the Mississippi’s west bank batture, the area between the water and the levee. That system, powered by diesel pumps installed at 3- to 4-mile intervals, is designed to pull fresh water from the river north of Kenner to the West Bank Water Treatment Plant.
Jefferson Parish spokesperson Rachel Strassel announced in a press release Thursday that the line had been successfully tested this week.
Meanwhile, in Orleans Parish, plans for a much bigger and more expensive pipeline have been put on hold. That pipeline would have delivered water to the Carrollton water treatment plant, at a cost estimated to be upwards of $250 million.
In its latest forecast Thursday, the U.S. Army Corps of Engineers predicts that salt levels will not exceed the safe-drinking threshold of 250 parts per million at any of the five water treatment intakes in Orleans and Jefferson parishes.
The Sewerage and Water Board of New Orleans is continuing with plans to prepare the parish’s southernmost intake, which draws water for the Algiers water treatment plant, for the possibility of having to treat briny water in case the forecast changes. Because that plant provides a significantly lower volume of water than the Carrollton plant, a pipeline is not needed, and officials are preparing instead to barge water to the facility if it becomes necessary.
They plan to construct a cofferdam — a barrier that encircles the intake to hold back some of the briny river water — and pump fresh water from barges into that structure, where it will be mixed with salt-contaminated river water to achieve the proper salinity level. The city has received bids for that work, has identified a contractor, and will have until early December to accept the offer.
The project is expected to cost roughly $20 million and would take no more than 30 days to build, said Steve Nelson, deputy general superintendent of the city’s sewerage and water board.
“We will resume mitigation efforts should the timeline shift in the coming weeks,” said Grace Birch, the department’s spokesperson.
Since the wedge first began to threaten the city, the agency and several other federal, state and local authorities, has been regularly testing river water for chloride levels. Birch urged the public to visit the board’s website for test results, resources, and the latest updates.