The six-passenger cart bounces across the rocky ground as we travel through a dark tunnel. Embedded crystals on the walls and ceiling sparkle, catching the light from the miner’s lamp on my hard hat, part of the stylish ensemble of protective gear issued to me before this journey began. The weight of the emergency breathing device in my safety vest pocket serves as a reminder that between me and the Earth’s surface are more than 2,100 feet of rock and salt.
I am deep inside the Waste Isolation Pilot Plant, or WIPP—a transuranic waste repository in the remote desert of southeastern New Mexico. I have joined a handful of my Los Alamos National Laboratory coworkers to learn more about our Carlsbad-based colleagues who work at the site, which opened in 1999.
About 250 million years ago, the Permian Sea covered this part of the desert. Over time, repeated evaporation cycles created a thick salt bed, forming an ideal, geologically stable environment for storing low-level radioactive waste. Most of the waste consists of things like contaminated clothing, equipment, and gloves used for nuclear weapons work dating back to the Manhattan Project.
Operated by the U.S. Department of Energy, WIPP is the only waste disposal facility of its kind in the nation. Waste arrives at WIPP weekly from “generator sites” across the country, where trained operators pack it into sealed containers that are then placed into larger, specially designed shipping containers as approved for use by the U.S. Nuclear Regulatory Commission. The journey from Los Alamos to WIPP is 315 miles, but some shipments travel from as far away as Idaho and South Carolina.
Once unloaded at the repository, the waste containers head 2,150 feet underground where they are placed in 300-foot-long tunnels that have been mined through the ancient salt formation. The surrounding salt eventually encapsulates the waste containers, permanently isolating them. Today, 25 years after it received the first shipment, the facility is approximately 44 percent full.
Doug Weaver, the Lab’s division leader for Repository Science and Operations, is leading the visit underground, which began when we entered the large, cage-like, hoist-operated conveyance that also transports waste drums to their final resting place. “Salt is a great natural barrier,” Weaver says. “This is the perfect geologic media for disposal of defense-related transuranic waste.” In 2023, Los Alamos sent 68 shipments to WIPP. That number could increase as Los Alamos continues the cleanup of various locations and begins production of plutonium pits—the cores of nuclear weapons.
WIPP employs more than 1,400 people, most of whom focus on waste disposal, but it’s also an experimental facility where scientists conduct research. Weaver is among the 50-plus Los Alamos employees who support WIPP and the National Transuranic Program. Scientist Shawn Otto, a member of the Test Coordination Office team, facilitates research that can only be done in this one-of-a-kind place. “Researchers have a section that has been mined out. Sometimes it’s referred to as Salt Disposal Investigations or the Underground Research Laboratory,” Otto says. “A lot of people at Los Alamos don’t know that this facility exists for research where salt is the right place to do certain kinds of work.”
Our cart rounds a corner and we disembark, walking deep into a tunnel to examine some of the research Otto helps facilitate. I lick my lips, tasting the salt that lingers in the air, as we walk toward a series of round holes bored into the salt wall. Tangles of wires emerge from the holes to transmit underground research data.
What kind of research is suited to taking place underground in a quarter-billion-year-old salt bed? “Physics-based experiments where you are shielded from cosmic and terrestrial radiation,” Otto says. The deep underground setting offers dry conditions and extremely low levels of naturally occurring radioactive materials, making it the perfect place for research on everything from particle astrophysics to geophysics. Other experiments examine how the salt bed reacts to storing heat-generating substances, which will help determine if salt deposits would be appropriate for storing different types of radioactive waste. “We take samples for laboratory studies and examine in situ the chemistry, hydrology, and geomechanics under thermal loads,” Weaver explains. Additional research areas “in the underground” involve operational testing of robotics, experiments focused on storing hydrogen, and studies of biological effects of small organisms in low-background radiation environments.
As we drive through what seems like a complicated maze of tunnels, Weaver, who clearly knows his way around underground, points out that the walls of the mine are always moving. In fact, at one point, the ceiling above us is bowed, hanging in a “U” shape. We pass small chunks of fallen salt and areas where the movement of the walls has caused rock bolts in the ceiling to break. Weaver assures us that the tunnels are routinely examined for structural soundness. “It is all constantly monitored,” he says. “Salt creeps continuously over time and is very predictable.”
Monitoring and regulations are as integral to WIPP as the salt is. The New Mexico Environment Department, the Environmental Protection Agency, the Department of Energy, and many other players ensure that everything that goes on at the facility is controlled and safe.
The visit ends with the opportunity to select a few golf-ball-sized chunks of salt from the mine to bring home as souvenirs. We gather around a pile, examining the pieces for trapped water bubbles. Once I’m back aboveground, I text a photo of my salt souvenirs to my daughter, and she asks, “Can I eat it?” The salt isn’t at all radioactive, but I still say “no.” ★