By Julie Leibach
Starting just outside Charlotte, North Carolina, a vast underground deposit of lithium stretches south for 25 miles. A key component of rechargeable batteries and energy grid storage systems, the soft, silvery metal is a global commodity, making this subterranean cache a geopolitically important and potentially lucrative resource.
Here, lithium primarily occurs within granite-like rocks called pegmatite, bound to a green-tinged mineral called spodumene. Two large lithium mines once operated in this region — “the Carolina Tin-Spodumene Belt” — but closed decades ago. As demand for renewable energy climbs, mining companies have growing interest in the area.
One of the country’s largest lithium deposits exists underground outside Charlotte, North Carolina.
The presence of historic, or legacy, lithium mines and the prospect of new lithium mining activity have led nearby residents to wonder about the possibility of drinking water contamination. Over the past several years, a team led by Avner Vengosh, Distinguished Professor and Nicholas Chair of Environmental Quality at Duke University’s Nicholas School of the Environment, has been working to address those concerns.
Building on research published in 2024, the researchers recently reported results from a study focusing on the water quality impacts of the two legacy mines, and of an active lithium processing site near Bessemer City, where raw lithium is converted into material suitable for lithium-ion batteries. The study, published in Environmental Science & Technology, was funded by the North Carolina Water Resources Research Institute and the Duke University Climate Research Innovation Seed Program.
“Our goal was to understand whether legacy mining and processing has affected the quality and chemical makeup of ground and surface water in and around the mines and through the Tin-Spodumene Belt,” Vengosh explains. “This research serves to keep surrounding communities informed about the potential water quality impacts of legacy mining operations.”
Detective Work
At the two historic mine sites — one is in Kings Mountain, the other near Bessemer City — vestiges of decades-long activity remain, including open pits, waste rock, and tailings, or the crushed rock left over after valuable material has been extracted.
For their study, the researchers collected 93 samples of groundwater — mostly from domestic wells — and 99 stream samples from inside and around the Tin-Spodumene Belt over a three-year period. Using tools developed by the Vengosh Lab, they analyzed the composition of each sample, looking for telltale chemical patterns, like detectives looking for fingerprints.
“When water interacts with different rock types, different elements can leach into the water. The ratio of certain elements in a water sample tells us something about the water-rock interactions occurring at the source,” explains Gordon Williams, the study’s first author and a Ph.D. student in the Vengosh Lab.
Communities living near historic lithium mines were concerned about the effects on drinking water.
Importantly, the team found no direct evidence of impacts on domestic well water from historic lithium mining and processing. Rather, they found that the natural geology of the area primarily affected the chemical makeup of groundwater.
Specifically, groundwater samples showed relatively high levels of lithium and the metals rubidium and cesium compared to average levels in North Carolina groundwater. Those higher levels likely stem from natural chemical interactions between groundwater and the pegmatite rock undergirding the area.
“Finding lithium in your well water doesn’t mean that you’re being contaminated. It means that you live in an area with the same type of rocks that lithium is found in,” Vengosh explains. “If you live in an area with pegmatite — regardless of whether lithium mining is occurring — the groundwater naturally will have relatively higher lithium than it will in an area that does not have pegmatite.”
As for surface water, the researchers found that streams near legacy mining and processing sites have relatively high levels of lithium and rubidium. Those levels probably did stem from the effects of legacy mining, and specifically from interactions between water and gypsum, a material found in lithium processing waste.
“It’s important to emphasize that, while we do see the impact of legacy mining on surface waters really close to historic mining and processing sites, that impact disappears due to dilution as streams flow away from these sites,” Vengosh says.
Water samples from domestic wells show no evidence of impacts from historic lithium mining, but nearby streams have relatively high levels of lithium and rubidium.
An outstanding question is what kind of health effects lithium and the two other identified metals — rubidium and cesium — might have on exposed individuals. The U.S. Environmental Protection Agency, which oversees the setting of acceptable standards for chemical contaminants, has not set limits for those chemicals. (It is worth noting that the U.S. Food and Drug Administration has approved the use of lithium for treating bipolar disorder, prescribed at far higher concentrations than those found naturally in the waters of the Tin-Spodumene Belt.)
Geology Matters
The team also tested groundwater for the presence of arsenic, a potent neurotoxin federally regulated by the EPA. Arsenic in groundwater can come from naturally occurring processes when water interacts with mine wastes or rocks that contain arsenic.
Although most samples contained arsenic below the federal drinking water standard, samples collected from a small cluster of neighborhood wells in Gaston and Lincoln counties showed levels far exceeding the federal standard.
A detailed investigation of underlying geology and its potential to impact water quality can inform the siting of future mines.
The area had previously been identified as an arsenic hotspot, so the findings weren’t a surprise. But the team wanted to know why arsenic levels were so high there.
After consulting geologic maps of the area, the team suggests that pegmatite rocks within the hotspot likely coexist with a different rock called mica schist, known to contain arsenic.
“We think that, as water interacts with the pegmatite, it creates conditions that enhance the leaching of arsenic from the mica schist, leading to highly elevated concentrations in the local groundwater, which is used by domestic wells in the area,” Williams explains.
Residents with affected wells are in the process of switching to municipal water, according to the team. But the study findings could inform decisions involving the placement of new lithium mines.
“Mine siting should involve a detailed investigation of the underlying geology and its potential to impact water quality,” Williams says. “If mica schist co-occurs with pegmatite, then that’s a potential recipe for water quality impacts from arsenic.”
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