DURHAM, N.C. — Leaks from carbon dioxide injected deep underground to help fight climate change could bubble up into drinking water aquifers near the surface, driving up levels of contaminants in the water tenfold or more in some places, according to a study by Duke University scientists.
Carbon capture and storage (CCS) from fossil fuel plants has many problems that constrain its ability to be even 10% of the solution to the climate problem (as discussed here). One of the biggest near-term problems is cost (see Harvard: “Realistic” first-generation CCS costs a whopping $150 per ton of CO2 “” 20 cents per kWh!).
But public acceptance (aka NIMBY) is also a huge problem — one that is likely to grow after the publication of this new study, “Potential Impacts of Leakage from Deep CO2 Geosequestration on Overlying Freshwater Aquifer” (PDF here).
What kind of contaminants could bubble up into drinking water aquifers: “Potentially dangerous uranium and barium increased throughout the entire experiment in some samples.”
Storing carbon dioxide deep below Earth’s surface, a process known as geosequestration, is part of a suite of new carbon capture and storage (CCS) technologies being developed by governments and industries worldwide to reduce the amount of greenhouse gas emissions entering Earth’s atmosphere. The still-evolving technologies are designed to capture and compress CO2, emissions at their source — typically power plants and other industrial facilities — and transport the CO2 to locations where it can be injected far below the Earth’s surface for long-term storage. The U.S. Department of Energy, working with industry and academia, has begun seven regional CCS projects.
“The fear of drinking water contamination from CO2 leaks is one of several sticking points about CCS and has contributed to local opposition to it,” says Jackson, who directs Duke’s Center on Global Change. “We examined the idea that if CO2 leaked out slowly from deep formations, where might it negatively impact freshwater aquifers near the surface, and why.”
Jackson and his colleague Mark G. Little collected core samples from four freshwater aquifers around the nation that overlie potential CCS sites and incubated the samples in their lab at Duke for a year, with CO2 bubbling through them.
After a year’s exposure to the CO2, analysis of the samples showed that “there are a number of potential sites where CO2 leaks drive contaminants up tenfold or more, in some cases to levels above the maximum contaminant loads set by the EPA for potable water,” Jackson explains. Three key factors — solid-phase metal mobility, carbonate buffering capacity and redox state in the overlying freshwater aquifer — were found to influence the risk of drinking water contamination from underground carbon leaks.
The study also identified four markers that scientists can use to test for early warnings of potential carbon dioxide leaks. “Along with changes in carbonate concentration and acidity of the water, concentrations of manganese, iron and calcium could all be used as geochemical markers of a leak, as their concentration increase within two weeks of exposure to CO2,” Jackson explains.
The study was funded by the Department of Energy’s National Energy Technology Laboratory and Duke’s Center on Global Change.
The release notes:
“Based on incubations of core samples from four drinking water aquifers, we found the potential for contamination is real, but there are ways to avoid or reduce the risk,” says Robert B. Jackson, Nicholas Professor of Global Environmental Change and professor of biology at Duke. “Geologic criteria that we identified can help determine locations around the country that should be monitored or avoided.”
I doubt that monitoring by itself is going to satisfy many local residents — especially with the growing concern about impacts on fresh water from natural gas fracturing. The fact that you may be able to detect a leak early isn’t the issue — the issue is whether your detection of the leak can lead to actions that would stop the leak, when it might just be too late.
What will need to happen, I think, is to see if there are a set of geological criteria that allow one to minimize or avoid this problem entirely. This problem may not turn out to be fatal to CCS, but might well limit the places where sequestration is practical — either because the geology is problematic or the site is simply too close to the water supply of a large population.