|
State officials have been fighting to hold off that fate, but it has taken a decade to research the problem and find funding to fix it. (The well’s owner, I W Inc., filed for bankruptcy in 2010, and officials are not pursuing its potential liabilities.) Last year, the pieces finally came together, and an unprecedented remediation effort began. But the work unveiled subterranean secrets: The size and shape of the cavity isn’t what previous studies suggested, and this means it will be more costly to remediate. No one knows how long it will be before the ground gives way.
New Mexico’s statewide survey of brine wells gave scientists a rare chance to identify an area in danger of imminent collapse. Most other parts of the country have not been studied as closely, though risk exists there, too. Roughly 35 percent of the United States is underlain with karst, a landscape characterized by a network of sinkholes and caverns created when groundwater — or the chemicals it carries — dissolves the subsurface geological layers. States and the federal government don’t track the damage, making it tricky to pinpoint the frequency and cost of sinkholes. Still, the National Cave and Karst Research Institute, a government-supported nonprofit headquartered in Carlsbad, conservatively estimated the damage due to sinkholes at more than $300 million each year.
Carlsbad offers an extreme and completely human-caused example of the potential danger of sinkholes and how difficult — and costly — they are to prevent or mitigate.
Any number of human activities can disrupt underground karst, explains Jim Goodbar, who worked for the U.S. Bureau of Land Management (BLM) as a karst expert for 38 years. Rain gutters and highway runoff trenches can route water to one spot repeatedly, eventually wearing through the Earth’s surface open to cavities below. And pumping large amounts of groundwater can disrupt the water table, which in turn, destabilizes karst.
Florida is considered the hardest hit U.S. state, but other sinkhole-prone states include Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. In 2019, scientists used aerial surveys to find a cluster of 19 giant sinkholes, most of them more than 35 million cubic feet, in southern China, likely caused by underground rivers in the karst system in which they formed.
The big events draw headlines, but minor subsidence events, where the ground slumps slowly into a void, are a more common, constant and overlooked problem. When Goodbar was with the BLM, he recalls getting one or two calls a year about sinkholes in roads or near pipelines where water was channeled until the ground gave way.
“It’s a quiet disaster that we just don’t see hitting us all at one time in one place,” says George Veni, the National Cave and Karst Research Institute’s executive director and a member of the state-led group overseeing the brine well.
Carlsbad sits on the edge of the Permian Basin, an underground geological formation that stretches from southeastern New Mexico to West Texas and accounted for more than 35 percent of the U.S.’s domestic oil production in 2019. The surrounding desert is lined with rows of pumpjacks and the occasional white tower of a drilling rig. Carlsbad’s streets, like those in Lubbock, Midland, and Odessa, Texas, are crowded with the auxiliary businesses that supply that industry with water, sand, chemicals, and equipment.
Brine is one of those businesses. Drilling a well requires fluid — typically composed of water and chemical additives — to lubricate the bit. But in the Permian, a layer of salt, called the Salado formation, rests between the Earth’s surface and the desired fossil fuel reserves. Instead of staying in line with the drill bit, water will soak into that salt — unless the water is already saline. Brine wells in the region, therefore, help meet the needs of the local oil and gas industry.
People have mined salt through wells for thousands of years — one source notes that the first recorded brine well was sunk in China more than 2,200 years ago — and still do at thousands of sites around the world. In the U.S., the Environmental Protection Agency lists 165 permitted “solution mining” sites, with about 18,500 wells in operation, the majority of which mine uranium.
“Whenever you’re doing a brine well operation like that, you’re dissolving the salt out, you’re creating an artificial cave in the subsurface which could become unstable,” says Lewis Land, a hydrogeologist with the National Cave and Karst Research Institute who conducted some of the early geophysical surveys on the brine well near Carlsbad. “Everywhere you find salt in the subsurface, you’ll almost inevitably find brine wells.”
This is the case beyond the Permian Basin. In 2012, a salt dome in Louisiana being mined for brine punctured through to the bayou above, sucking down water and cypress trees and quickly spreading to impact 36 acres and force 350 people to evacuate their homes for years.
Operators often add a layer of oil or diesel fuel that floats on the saltwater and buffers the ground, preventing it from dissolving, Land says. That way, he says, “it’s less likely to collapse. That methodology is not practiced in New Mexico.”
In March 2009, regulators, technical experts, and industry representatives gathered in Santa Fe and concurred with Griswold’s conclusion: The I W well was likely to collapse. In June of that year, the state installed an early warning system. On the highway, drivers pass a yellow and black sign cautioning that the road ahead is “subject to sinkhole.” On-site sensors monitoring the site are sensitive enough to register distant earthquakes, local rush-hour traffic, and, the hope is, rocks falling inside the cavity. That should give hours of notice to stop traffic on the highways and evacuate the area.
“I know people who have told me they won’t drive along that stretch of highway for fear that suddenly they’re in space, falling into a big hole in the ground,” Veni says. “I think the odds of that are incredibly slim.”
Were it to collapse, the costs to refill the hole and repair the roads, rail line, and businesses, plus the lost business, freight traffic, crops supplied by the irrigation canal, tourism to the nearby Carlsbad Caverns and Guadalupe Mountains national parks, and tax revenue could total $1 billion. Before remediation work began, geophysical data suggested the ground could fail as soon as 2021.
|
