Navigating Murky Waters: Tackling Saltwater Intrusion in Southeastern Louisiana
With the gentle lull of waves and sunset light dancing across the surface, it’s no wonder living by the ocean is a dream for many Americans. Combined with economic opportunities at the water’s edge, nearly 12.5% of the world’s population lives less than 10 meters from the high tide line, and the beach is the leading tourist destination in America. Still, something dark lurks beneath the surface. With sea-level rise, droughts, and the increased intensity of large storm events due to climate change, saltwater intrusion is an imminent threat to our drinking water infrastructure. Making matters worse, surveys show that only 10% of drinking water utilities have a climate adaptation plan—and most are in California.
What’s Going on in Southeast Louisiana?
For folks living in southeastern Louisiana, along the Gulf of Mexico, their home is synonymous with the growing number of deteriorating coastal ecosystems battered by hurricanes, floods, and sea-level rise. Climate-related threats have resulted in the loss of one football field of wetlands every 100 minutes in this area. With less protection from rising seas, residents in the area are always worried about whether water coming from their faucet is safe for their plants, for cooking and bathing, or just taking a sip themselves. Last summer, droughts along the Mississippi have resulted in the landward movement of a “saltwater wedge”—which has breached what’s called an underwater sill (pictured below), in effect contaminating drinking water supplies for coastal communities downstream of New Orleans. Utilities that pull water from the Mississippi River are at risk of contaminating their supply with saltwater as the wedge moves inland. Saltwater, of course, is undrinkable without significant treatment (i.e., reverse osmosis or distillation) and can’t be boiled out.
At its worst, drinking water was found to be 6.5x saltier than EPA’s recommended threshold, and a state of emergency was declared for communities in Plaquemines Parish (located closest to the Gulf) last June. Ms. Bette Billiot, a member of the United Houma Nation and Sierra Club, is an expert community organizer and strong advocate for the residents of Plaquemines Parish. She’s conveyed the stories of locals impacted by this issue since then: residents noticed poor water pressure in their homes, gardeners noticed declining plant quality, fishermen couldn’t produce ice to transport their catch, and small business owners spent thousands to replace rusty machinery and pipes damaged by water salinity just to stay open. In one telling, salty water caused a water heater to corrode so much that it needed to be “completely replaced within a matter of about 3 months.”
What’s more, large construction operations like the liquefied natural gas (LNG) terminal—which pulls up to 100,000 gallons of freshwater/day from the parish—exacerbate existing freshwater availability issues within this community. The use of salty water for construction can also present structural problems for the LNG terminal—and, when coupled with existing water stress, has placed the project squarely in the category of a “threat to public welfare” in the minds of many community members.
Why Should We Care About Saltwater Intrusion?
At the most basic level, saltwater wreaks havoc on drinking water infrastructure: it corrodes old lead pipes, which introduces harmful chemicals into our drinking water (Louisiana has an estimated 56,000 lead service lines that serve 4.7 million people), and increased salt intake results in a myriad of other serious health problems. While the U.S. Army Corp of Engineers (USACE) barged in 20.77 million gallons of water and procured technology to desalinate 3.5 million gallons/day for the residents of southeastern Louisiana, the scenario points to a much larger national issue.
Challenges Across the Nation
While the federal government spent an unprecedented $32.3 billion on water infrastructure in FY23, the economic and health-related impacts of saltwater intrusion have yet to be prioritized. Without predictive tools to forecast and build proactive infrastructure, the reactive cost will inevitably be much higher. We’re already seeing the economic impact of aging infrastructure across the nation: the latest Drinking Water Infrastructure Needs Survey and Assessment estimated that nearly $422.9 billion will be allocated towards fixing deteriorating pipelines over the next 20 years—which is 14% higher than the last assessment. Worse, saltwater intrusion will only exacerbate existing threats to drinking water infrastructure and is already impacting coastal communities.
During a small quantitative analysis on how this issue is impacting southeast Louisiana, I discovered that there is still much we need to do to evaluate the threat saltwater intrusion poses to water utilities:
For instance, we lack an accurate understanding of water utility service area boundaries across the nation. Many states, including Louisiana, maintain a private database of their service area boundaries. While we were able to estimate these boundaries across the U.S., we’re missing information for approximately 48% of the population in Plaquemines Parish. Public access to these boundaries would allow us to build models to understand who is—or will soon be—affected, to respond sooner to these intrusion events, and to direct funds to utilities that need them.
It’s also clear that if we don’t know who already has access to clean drinking water, we won’t be able to tell who is (or will be) impacted by saltwater intrusion.
Population of Plaquemines Parish and Estimated Service Area Boundaries
Estimated population of Plaquemines Parish census blocks as colored polygons. Locations in yellow have more people than purple locations. Census blocks without populations were removed for the purposes of this map. Estimated service area boundaries are outlined in black and the boundary of Plaquemines Parish is shaded in gray.
We need interdisciplinary collaborations between surface, ground, and saltwater modelers to elucidate how salt moves through and across landscapes. The underwater landscape of estuaries can be very different—which influences water circulation and how salt and freshwater interact. Dr. Allison Lassiter, an Assistant Professor at the University of Pennsylvania, leads a lab that focuses on drinking water infrastructure. With a lot of these water suppliers sufficiently on the edge of these shifting salt lines in estuaries, she underscores that “getting all of [the dynamics] right matters.” Collaborations between these groups of scientists is necessary to accurately model the way salt moves within estuaries across the nation. The U.S. Army Engineer Research and Development Center’s technology to forecast salinity locations is a great example of successful collaborations between these groups, but a national predictive model is needed to forecast which water suppliers are or will be affected.
Water utilities often haven’t considered their own risk to saltwater intrusion. Dr. Lassiter surveyed 330 community water systems with water intakes and wells that would be inundated under a 3 foot sea-level rise scenario. Among the 110 survey respondents, approximately 25% believed they were at risk of salinization. At least one utility experienced salinization after the survey, when they previously reported they weren’t vulnerable.
Lastly, water utilities are often overwhelmed with other issues (e.g., keeping their systems in compliance, monitoring nearly 100 contaminants, maintenance, reporting, etc.), and saltwater intrusion is often not a threat on their radar. Building prioritization tools would help utilities better understand their risk and bring stakeholders together to build more resilient water infrastructure.
What Solutions Are Available?
Addressing these challenges and building a predictive saltwater intrusion model would help us prioritize communities in need of resilient drinking water infrastructure. Designing proactive infrastructure involves a mix of different strategies, such as water conservation techniques (i.e., improving water catchment, adopting water-efficient technologies); moving water intakes or utilities further upstream (which can cost millions); constructing sills and barrier wells; and desalinization technology.
California’s Water Resilience Portfolio is a shining example of how a state long affected by water shortages has embraced a variety of technologies to address unique regional water needs. In San Diego, for example, the construction of the largest desalination plant in the Western Hemisphere, Poseidon, provides 10% of the drinking water supply. While desalinization technology is an attractive solution for saltwater intrusion, reverse osmosis systems are expensive and might not be affordable for smaller water utilities. These factors are important to consider when designing resilient water portfolios for communities affected by saltwater intrusion.
Turning back to Louisiana, while officials say water throughout Plaquemines Parish is now safe to drink—after reverse osmosis and the barging of freshwater by the USACE—local community members remain wary. Nonprofits continue to distribute water and warm meals for residents, and lead testing is ongoing throughout the parish. Yet Plaquemines, and other small coastal communities like it, generally have less access to resources and capacity to manage salty drinking water. Building a national predictive model—although not simple—is one way to proactively identify vulnerable communities like Plaquemines, and to prioritize where resilient water infrastructure is needed. And with affected places like Louisiana and others across the nation, it’s clear that when it comes to solutions, we can’t afford to wait.