Corpus Christi’s First Water-Desalination Plant Could Create “Dead Zones”
The dark hump of a bottlenose dolphin’s back cuts through the surface of the Corpus Christi Ship Channel, appearing briefly alongside a docked, Hong Kong–registered bulk-cargo vessel. This industrial canal is an unlikely haven for wildlife, but dolphins are attracted by its cool waters and abundant mullet and appear so regularly that local captains take tour boats to see them.
From the observation tower under the downtown Harbor Bridge, a pedestrian can also spy the bend in the channel, a mile and a half away, where the city is placing pipes to feed its planned Inner Harbor desalination plant. Water will be sucked into the facility and stripped of its salt and other minerals by reverse osmosis. The clean water will be routed into the city’s system, and from there into faucets, factories, and toilets throughout the area. Pollutants such as mercury and lead will be removed from the salty remainder before it is released to flow back into Corpus Christi Bay. City consultants estimate that between 35 million and 50 million gallons of dense, briny discharge will be produced each day, enough to fill as many as 75 Olympic-size swimming pools.
Texas Commission on Environmental Quality spokesman Ricky Richter, responding to a Texas Monthly inquiry, provided the precise GPS coordinates for the place where this discharge will be released, a spot designated as Outfall 001, about two miles up the shipping channel from the bay. Other cities with desal plants, such as Carlsbad, in California, and Ras Al Khair, in Saudi Arabia, avoid dumping their discharge into coastal bays and instead send it into deeper bodies of water.
The city maintains that the Inner Harbor project will have “negligible impact to Corpus Christi Bay and aquatic life.” But Outfall 001 sits right where experts have warned the discharge could create suffocating “dead zones” for marine life, including dolphins and the smaller fish and shellfish on which they feed. Other researchers caution that the modeling used by the city to predict the outfall’s reach is giving state regulators an incomplete view of the plant’s impact.
When the three commissioners of the TCEQ—all appointed by Governor Greg Abbott, with the consent of the state Senate—vote early next year on whether to approve a discharge permit for the project, the health of Corpus Christi Bay could be at stake. And because the Inner Harbor project would be the state’s first large seawater-desalination plant, what happens here may guide how other plants get built in water-starved Texas.
Corpus Christi’s water sources are falling treacherously short of the area’s demands. The Nueces River feeds Lake Corpus Christi, the city’s primary reservoir; Corpus also draws from Choke Canyon Reservoir, near where the Frio River flows into the Nueces. Both reservoirs are ailing from extended drought, with Lake Corpus Christi at about 27 percent capacity and Choke Canyon down to just 17 percent, as of early December.
Such conditions are expected to continue, and the city anticipates major water shortages starting in 2030, though not because of population growth. The number of Corpus Christi residents has declined slightly since 2020, even as much of the rest of Texas boomed, according to the U.S. census. Some private firms predict the city’s population will increase about 3 percent by 2030, and city projections indicate little to no growth through 2050. Residential demand is likewise expected to remain nearly flat across the eleven South Texas counties that encompass the state water planning authority’s Region N, of which Corpus is the largest city.
At the same time, the region’s unmet water needs for industrial users—mainly driven by the petrochemical industry—are set to more than double in the decades ahead, according to the state’s latest water plan, drafted in 2022. The region’s industrial customers already use about half of the available water. The Valero refinery near downtown Corpus Christi and the nearby ethylene-cracker plant, co-owned by ExxonMobil and Saudi Basic Industries Corporation, together use 25 percent of the system’s water.
Corpus Christi officials see a growing industrial base as key to the Coastal Bend region’s economic future. For the past five years, the system’s “large-volume industrial customers” have forked over an extra 25 cents per thousand gallons above their regular rates to fund a new water supply, officials say. That’ll increase to 31 cents per thousand gallons beginning January 1. For the money they’ve paid, these companies expect new water-bearing infrastructure.
Five desalination projects are in the planning stages around Corpus Christi Bay, but leading the pack is the Inner Harbor plant, which is expected to generate at least 30 million gallons of potable water daily after it’s completed, in 2028. Most of that water will go to industrial users, but it would be enough to supply the needs of about 100,000 households. (Corpus Christi’s water system supplies about 500,000 residents within a seven-county service area.)
In October the city awarded a contract for the Inner Harbor plant’s design and construction to Kiewit Infrastructure South, a branch of a commercial construction company based in Omaha, Nebraska, at a cost of $757.6 million. The Texas Water Development Board granted the city $535 million in low-interest loans to help finance the project.
The chosen location of the desalination plant in Inner Harbor has raised the ire of some in the adjacent Hillcrest neighborhood, and environmental and community groups are rallying against the facility, so far to little avail. The U.S. Department of Housing and Urban Development looked into potential civil rights violations regarding the placement of the plant alongside historically Black and Latino neighborhoods; it closed the probe after two years but reopened it late this year.
Yet the Inner Harbor location is hardly a surprising choice, considering that the area has long been overrun by industrial and municipal infrastructure, including Citgo refineries and water-department wastewater-treatment facilities. “The proximity of this plant to our existing water system eliminates the need for extensive new piping, providing significant cost savings,” an official in Corpus Christi’s water department told Texas Monthlyin a written response to queries. The city declined to make any officials available for interviews.
However attractive the savings may be on land, the location’s impact offshore may pose problems when the bay begins trying to absorb tens of millions of gallons of briny discharge each day.
The consulting firm Freese and Nichols, to fulfill requirements of a contract with the city, commissioned two Texas A&M–Corpus Christi scientists in 2019 to investigate how the Inner Harbor plant could affect local waterways. Because many marine animals, such as fish and shellfish, in their earliest stages of life depend on estuaries—where ocean waters mix with fresh water from the mouth of a river, as in Corpus Christi Bay—the researchers determined that releasing the discharge into the Gulf of Mexico’s deeper, more turbulent water was the best option. “Locations within the bay present many more potential environmental concerns that may not be easily minimized or mitigated,” they wrote in their report, adding, “A confined area like a canal or channel where dilution or mixing is limited . . . could create a water quality issue.”
A&M–Corpus Christi staff declined Texas Monthly’s interview requests. One of the potential dangers the report noted was that the desalination plant’s discharge would be denser than the bay water, causing it to sink to the bottom as it flowed downstream from the shipping channel—which is fed by the Nueces River—into the more stagnant shallows of the bay. That layer of heavy brine could cause hypoxia, the technical term for the smothering of life due to a lack of oxygen. “It causes fish and pretty much everything else to die,” says Kristin Nielsen, an aquatic toxicologist and assistant professor at the University of Texas’s Marine Science Institute.
An ideal discharge location, like those of many other desalination plants in other states and countries, would be along a long underwater slope where there’s a steady exchange of discharge with open water. Such slopes keep the brine from settling on the bottom like a salty blanket. Unfortunately, because Corpus Christi Bay is relatively shallow throughout, water entering the bay tends to linger. It has what scientists call a “residence time” of about a year before it makes its way out to the open sea. “We don’t have the change in depth along the bottom that you would typically see near a well-sited outfall that helps that plume to break up,” Nielsen says. She describes the placement of Outfall 001 as “genuinely shocking.”
Despite the advice of the A&M researchers, Freese and Nichols produced a white paper arguing that the discharge should flow into the shipping channel. Corpus Christi’s water department says a jet diffuser—a device with nozzles that dilute the salty discharge with bay water—will mitigate the hypoxia risk. The diffuser will be placed at the site of Outfall 001, 32 feet below the surface, near the bottom of the 45-foot-deep channel.
The city’s professed faith in diffusers appears unshakable, with a spokesman saying they’ve “proven effective in various successful plants worldwide” in a statement about the project. Perth, Australia, is cited by Corpus Christi as an example of a city with a desalination plant that has used jet diffusion and has reported no negative impacts from nearly twenty years of discharging effluent into an environmentally sensitive body of water.
There are similarities between Perth’s plant and the proposed Inner Harbor one. Perth’s produces 12 billion gallons of drinking water a year, while Corpus’s would create about 11 billion. The locations also similarly involve contending with the interplay of an inflowing river, a bay, and the deeper water of the sea. But Perth’s Cockburn Sound gradually gets deeper on average, going from about 30 feet to 72 feet. Corpus Christi Bay has an average depth of around 11 feet and reaches a maximum of only about 16 feet. So the changes in depth in Cockburn Sound may account for Perth avoiding the environmentally negative effects the A&M researchers flagged as a potential problem in Corpus.
The city also compares Inner Harbor to Tampa Bay’s Seawater Desalination Plant, in Florida. There, according to the Tampa Bay water department, discharge from the diffusion process is routed through a purpose-built canal, which increases mixing. This system is more elaborate than the proposed Inner Harbor one, which seemingly depends on jet diffusion alone. Tampa Bay also enjoys a heavy volume of water that naturally surges in and out of the area where the desalination plant is located, courtesy of tides and rainfall, making the comparison to the sluggish water of the Corpus shipping channel imprecise in a vital way. Kiewit, which is still in negotiations over the cost and design of the project, referred all questions about the design to the city.
Nielsen acknowledges that seawater-desalination plants have track records of successfully balancing water needs against environmental impacts, but she notes that such plants are in places where the underwater environment is better suited to dumping saline into a bay. She and others warn that the evaluations used by the city—and provided to the TCEQ—understate the environmental risks.
One of the state’s leading experts in hydrological modeling, environmental engineer Ben Hodges of the University of Texas at Austin, has studied the effects of high salt levels in Corpus Christi Bay and found signs of oxygen deprivation already present. In a 2011 paper published in the Journal of Hydraulic Engineering, he wrote that a steady saline discharge from the proposed site of the Inner Harbor plant would likely cause hypoxia in areas distant from the outfall—even as far as the bay’s opposite shoreline, about fifteen miles away.
Another ocean engineering expert, Scott Socolofsky of Texas A&M in College Station, reviewed the Inner Harbor project’s TCEQ submissions, at the request of the environmental group Earthjustice, in June 2024. He found that the city’s modeling “assumes the discharge is well-mixed over the whole cross-section of the Inner Harbor channel,” which he said is unlikely to happen.
More concerning, Socolofsky found that the models submitted to the TCEQ are only useful for predicting impacts directly at the outfall and ignore the effects farther away. Socolofsky advocated for a battery of new models to be created. “This is needed to understand the extent and persistence of the region affected by the discharge,” he wrote in an exhibit presented to the state regulators.
Indeed, the city’s environmental discharge study from 2021 focuses on the area immediately surrounding the outfall. It includes Freese and Nichols’ predicted stats for the discharge, registering a salinity of 42 parts per thousand at fifty feet from Outfall 001 and 35 parts per thousand—within the bay’s range of average salinity—at two hundred feet. Data on what happens to the brine beyond that distance is notably lacking, with the discharge and bay water presumed to entirely mix. This assumption is exactly what Hodges and Nielsen and the A&M researchers doubt will happen.
The TCEQ has already awarded a permit for the Inner Harbor project to use bay water, which by law is owned by the state, but the discharge permit remains pending. “Permit applications require the applicant to consider local environmental conditions,” Richter said of the state’s process. “All permit applications undergo a rigorous technical review, and wastewater permits are drafted in accordance with the Texas Surface Water Quality Standards.”
Those standards do not set hard limits on releasing brine into estuaries, such as Corpus Christi Bay, because of natural variability in salinity. But they do require that any changes in salinity support aquatic life. This flexibility leaves the limits open to interpretation by cities and their consultants. If Corpus Christi makes bad assumptions using poor models and the state allows it, proposals for other desalination projects, such as a proposed plantnear Freeport, could do the same.
Since there’s no indication that the Inner Harbor plant will violate the federal Clean Water Act, which governs the release of pollutants, the U.S. Environmental Protection Agency has deferred to the TCEQ’s judgment of the Inner Harbor plant’s impact. That leaves Texas regulators to safeguard the bay, even as the state is helping pay for the desalination project. Officials recognize that the decisions made about the pioneering Inner Harbor project may set the bar for future seawater-desalination plants in Corpus Christi—and across Texas. “There are a lot of eyes on this project,” the state’s Water Development Board chair, Brooke Paup, told city officials during a public meeting. “You are a test case—so make it work.”
