Coleen Kaska is a member of the Havasupai Tribe, whose village deep in the Grand Canyon depends on nearby springs and seeps as its sole source of water. Several of the springs also feed Havasu Creek, which runs through the village of Supai and forms the turquoise waterfalls that bring thousands of tourists to the Havasupai reservation each year, sustaining the tribe’s economy.
“For 30-plus years this has been a struggle to protect our aquifer that feeds the river in our village,” Kaska said Wednesday night at a forum on uranium mining at the Museum of Northern Arizona. Many who oppose uranium mining in the Grand Canyon watershed say it risks contaminating groundwater sources with enough uranium that the connected springs and seeps would be unsafe for the plants and animals those water sources sustain.
A lack of evidence supporting or refuting that concern was one of the driving factors in the Obama administration's 2012 decision to withdraw nearly 1 million acres near the Grand Canyon from new mining claims.
Both before and after the withdrawal decision, researchers have fanned out across the Grand Canyon to study the region’s groundwater system and the possible connections between mining and water sources. Five years later, the science is still far from providing a definite answer, said Fred Tillman, who leads the U.S. Geological Survey team tasked with looking at the potential impacts of uranium mining on water resources.
Opponents of uranium mining often cite a 2010 USGS report that five wells and 15 springs in the region were found to have uranium levels above the federal drinking water limit, including springs and streams near two now-closed uranium mines from the Cold War era. On top of that, a research team from the University of Nevada Las Vegas measured uranium levels in the creek near one of those mines, the Orphan Mine, whose shaft was first sunk in 1906, that were more than three times the drinking water limit.
But those high uranium concentrations aren’t unequivocally related to mining — they could be due to natural processes too, or a mixture of both, the same 2010 USGS report said. The ore at the Orphan Mine, for example, is an ancient exposed breccia pipe on the side of the South Rim cliff face. And a January study found that uranium concentrations three times the drinking water limit measured in Pigeon Spring are more likely related to natural sources than the nearby, Pigeon Mine, which many had suspected. The mine, now closed, operated from 1984 to 1991.
At the same time, researchers are producing findings that cast doubt on assurances by mining advocates that breccia pipe uranium mining isn’t a risk to water sources because hundreds of feet of impermeable rock separate the bottom of the mine shaft from the deeper regional aquifer.
In fact, studies are showing that water falling on the surface can reach deep underground aquifers and then emerge in springs and seeps within a matter of days.
DISTURBING THE SYSTEM
As it migrates downward, water naturally comes into contact with the uranium ore-rich breccia pipes. In their undisturbed state, the pipes are a low-oxygen environment that causes uranium to precipitate out of water as crystals that aren’t prone to mobilize, said David Kreamer, a hydrologist at UNLV who has spent decades doing water studies like those near the Orphan Mine.
Mining the pipes changes the game, he said.
Inserting a mine shaft into the area and introducing oxygen into the deeper geologic layers “throws the chemical balance back into dissolve mode,” increasing the ability for the uranium to redissolve into water and migrate, Kreamer said.
Water isn’t supposed to migrate into modern mines during operations — the underground tunnels, openings and shafts are meant to be dry. But that isn’t always the case.
This spring, Canyon Mine pierced a shallow aquifer with its drilling activities, causing water to seep into the shaft that operators have had to pump out. A volume equivalent to what would come from a constantly running garden hose continues to enter the shaft, and last spring the spokesman for Canyon Mine's owner, Energy Fuels Resources, said that uranium concentrations in the water were found to be about three times drinking water limits.
Across the canyon at Pinenut Mine, the owner reported in 2009 that 2.8 million gallons of water had accumulated in the mine shaft since it was put on standby in 1989. That had to be pumped out as well.
Once mines are closed and reclaimed, they are supposed to be capped and the shafts refilled with wasterock. But there is no stopping groundwater from flowing into the voids left in the shaft and the mined pipe where it could pick up remaining uranium ore, Tillman said.
“It seems impossible to keep water away,” he said.
Energy Fuels spokesman Curtis Moore agreed that water will likely seep into the mine and shaft over time, but won't be able to reach the deeper aquifer due to impermeable rock.
“Energy Fuels and our regulators are confident that the Canyon Mine will have no impact on water,” he wrote in an email.
Researchers studying the area describe a varied and unmapped network of groundwater connections beneath the Coconino Plateau.
“(Water) will find fissures and cracks and other structures and find its way down to regional aquifer,” Tillman said.
Other findings support that description.
One study of an exposed breccia pipe in Grand Canyon National Park found fractures extended from the bottom of the breccia pipe down to the bedrock.
“So if stormwater were to penetrate the breccia pipe it could find its way all the way down to groundwater,” said Malcolm Alter, a former geologic engineer who authored the study.
His study didn’t examine whether similar fractures extend from other breccia pipes, but Alter said the way to make sure water doesn’t pass from uranium rock to groundwater is to keep the mines dry.
Other studies on the north rim of the Grand Canyon suggest that water’s movement from surface to aquifer could be happening over a matter of days or weeks. For three years, Grand Canyon National Park hydrologist Ben Tobin has been putting fluorescent dye in sinkholes on the Kaibab Plateau, then tracking drainages and springs in the canyon to see where the dye turns up. In one test, it took less than a month for dye injected on the Kaibab Plateau to turn up in water sources as far as 26 miles away and 6,000 feet lower than where it began, Tobin said.
Another study by a graduate student at Northern Arizona University showed that after a monsoon event, it took just days to measure a response in springs fed by the regional aquifer, Tobin said.
There’s an important caveat that the behavior of groundwater and springs on the South Rim may be much different than what’s being observed on the North Rim and the underground structures of sinkholes may be different than breccia pipes, Tobin said. From what he has seen so far, Tobin said the 1,000-plus feet of rock between the breccia pipe mines and regional groundwater may be an impenetrable barrier in some cases but in other cases it clearly is not.
Other research, including projects led by Kreamer from UNLV, is looking at connections between mines and the shallower perched aquifers. One of Kreamer's projects found the characteristics of water near Canyon Mine mirror those of water coming out of Grapevine Springs in the Grand Canyon — a sign the two could be connected, Kreamer said.
Frank Bain is a mining consultant who has worked in uranium exploration near the canyon. Even if groundwater comes into contact with uranium mines and then reaches the regional aquifer below, it will get so diluted that the impact will be negligible, Bain said.
Tobin’s studies of groundwater flows beneath the Kaibab Plateau aren’t advanced enough to measure dilution, so they couldn’t determine how uranium present in water at the surface, for example, might be diluted by the time it makes its way into the regional aquifer, he said.
In a general sense, though, the drastic scenarios of uranium mines contaminating the Colorado River are unlikely, at least based on current data and mining activity, Don Bills, a USGS hydrologist in Flagstaff, said in a 2014 interview. Springs and creeks that have recorded high uranium concentrations have ephemeral or very small flows so by the time they reach the river, their waters are so diluted that any elevated uranium concentrations are “essentially impossible to detect,” Bills said.