Work begins to raise barrier against salt water pushing up Mississippi, threatening water supplies

Work to elevate a saltwater barrier in the lower Mississippi River has begun, but it will only stall rather than halt the creeping threat to water supplies in the New Orleans area.  

The earthen sill near Alliance in Plaquemines Parish will be raised about 25 feet from the height the Army Corps of Engineers originally built it to in July, corps officials announced Monday. Once finished next month, the sill, which acts as an underwater dam, will be about 30 feet below the river's surface. It’s hoped that the sill will delay saltwater contamination in Belle Chasse and much of St. Bernard, Orleans and Jefferson parishes. 

On Monday, Gov. John Bel Edwards submitted a request for President Joseph Biden to declare the saltwater intrusion a federal emergency. If approved, the declaration would provide federal money to reimburse state and local spending to mitigate the issue and authorize assistance from the Federal Emergency Management Agency and other federal agencies.

"We have had discussions with FEMA about the unique challenges we face with this event," Edwards said. "We are optimistic the president will approve our federal emergency declaration, which will be crucial to help our communities along the lower Mississippi River."

As of Monday afternoon, the leading edge of salt water moving north in the river was at mile 69 near Jesuit Bend, about seven river miles downstream from Belle Chasse, which is preparing to receive increased freshwater flows from Jefferson. The sill is now about five miles downriver from the saltwater edge, meaning the sill has only slowed but not contained the intrusion.

With sill upgrades underway, the Army Corps estimates the salt water’s upriver progress will be delayed by 10 to 15 days. That means salt water may now reach water intakes in Belle Chasse around Oct. 13. 

The water supply for as many as 8,000 Plaquemines residents has already been affected by the salt water, Plaquemines council member Mitch Jurisich said. 

"It's been a horrible experience, especially for the citizens on the lower end of the parish," he said. "They've been suffering with this."

Unsafe levels of salt water could reach many New Orleans area drinking water intakes by mid-October, forcing officials to search for other sources of fresh water. The Corps of Engineers is planning to use barges to transport 36 million gallons of water per day from further upstream to local utilities. The same strategy was used during low-water periods in 1988 and 2012.

“This water can then be combined with water at the municipal facility to create a mixture that is safe for treatment,” said Col. Cullen Jones, commander of the Corps’ New Orleans District.

The barge plan aims to reduce salinity at intake facilities as far upriver as Gretna, which is expected to see intrusion by around Oct. 24 after first reaching facilities in Belle Chasse, Dalcour, St. Bernard Parish and Algiers. After Gretna, the salt wedge is forecast to reach facilities in Marrero, Westwego, the east bank of New Orleans and Metairie through the end of October.

Officials said another idea under consideration is to build a temporary pipeline from a point in the river near Kenner to the Carrollton treatment plant in New Orleans, and possibly connecting to those in Jefferson above Gretna. The cost, permitting requirements, rights of way and other complexities involved with that concept are not yet clear.

“We’re trying to be thinking about this from a regional perspective,” said Ghassan Korban, executive director of the New Orleans Sewerage & Water Board. “Any solution that could help an adjoining parish, in this case Jefferson, probably ranks higher in terms of feasibility and support, because two communities at the same time justifies the cost implications.”

Other options like reverse osmosis are also being considered, but Korban said such technology may not be feasible at a massive scale. In New Orleans, the Carrollton plant treats 150 million gallons per day, about 12 times the amount treated at the Algiers plant.

A lack of rain over the entire Mississippi River Basin, which includes 31 U.S. states and two Canadian provinces, has caused the river to drop to near-record lows in multiple states. As the river drops, the Gulf of Mexico moves in, making the lower end of the river increasingly salty. 

The sill was initially built for almost $9 million. The upgrades will still leave a 620-foot-wide gap in the channel to allow oceangoing ships to pass. That will also allow more salt water to move upstream.

The Corps is using dredged river sediment to elevate the sill. Full construction will likely take three weeks, but every inch added in the meantime helps slow the salt water's progress, Corps officials said. 

The intrusion of salt water into the river is a “naturally occurring phenomenon” because the bottom of the riverbed between Natchez, Mississippi, and the Gulf of Mexico is below sea level, according to the Corps. Because salt water is denser than fresh water, it moves upriver below the downriver flows.

Under normal conditions, the downstream flow is strong enough to push out the saltwater. Sills have been built during droughts and extreme low flows in in 1988, 1999, 2012 and last year.

In early July, Edwards declared a state of emergency for Plaquemines after the Boothville water system, which serves residents and businesses south of the Empire Bridge, was contaminated with salt water. The problem has only worsened in recent weeks, partly because the Port Sulphur water plant had not been repaired after it was damaged by Hurricane Ida in 2021, and local officials had trouble finding reverse-osmosis units, which remove salt, for its plants. 

But things are starting to improve, Jurisich said. The Port Sulphur plant is partially repaired and receiving water from barges. Barged water is also helping to dilute salty water at plants in Boothville and East Pointe a la Hache. 

A reverse-osmosis unit arrived at East Pointe a la Hache on Monday. Six more units have been ordered by the state Office of Homeland Security and Emergency Preparedness Water for three other Plaquemines plants. 

Water quality has improved enough at the Port Sulphur plant that some of its much-reduced supply is now flowing to Venice, at the far south end of the parish. 

Jurisich said help for Plaquemines ramped up last week when it appeared the salt water could harm water supplies in the New Orleans area. 

"It finally took a threat to New Orleans, St. Bernard and Jefferson Parish to get people to know that this was knocking on the door," he said. "I wish the severity of this was something we'd screamed a little louder about early on." 

If anything, it's a wakeup call for the region to upgrade water plants, expand pipeline networks and make other improvements.

"We've all got to prepare for the next go-around," Jurisich said.