Saltwater from the Gulf of Mexico is flowing up the Mississippi River. The saltwater flow has reached water treatment plant intakes for Plaquemines Parish, causing the drinking water to have elevated salt levels.
Drinking water at Port Sulphur had chloride levels of 362 mg/L and sodium levels in a range of 60 mg/L to 200 mg/L. Chloride is considered a secondary contaminant, meaning there is no risk to health, but it could affect taste, odor, or color of drinking water. The EPA has set a maximum contaminant level for chloride at 250 mg/L. While there is no maximum for sodium, people with health issues may need to get drinking water elsewhere.
The saltwater is flowing upriver this year because of the extensive drought in the central United States. With so little rain, Mississippi River levels are lower and the current is slower.
The Army Corps of Engineers devised a plan to install a sill across the Mississippi River to stop the flow of saltwater. A sill is a pile of dirt, much like an underwater levee. Saltwater is heavier than fresh water, so the sill will stop the saltwater flow, while allowing freshwater to continue moving downriver.
Sills have been used successfully in the Mississippi River before in 1988 and 1999. Sills are only temporary. Once the river returns to normal flow, the current will erode the sill fairly quickly.
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