Study looks at consequences of CCS leak

Storing CO₂ 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 to reduce the amount of greenhouse gas emissions entering Earth’s atmosphere.

The 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 Earth’s surface for long-term storage.

’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,’ said Prof Robert Jackson, who directs Duke University’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.

’Geologic criteria that we identified in the study can help identify locations around the country that should be monitored or avoided,’ he added. ’By no means would all sites be susceptible to problems of water quality.’

Jackson and his postdoctoral fellow Mark Little collected core samples from four freshwater aquifers around the US that overlie potential CCS sites and incubated the samples in their lab at Duke University for a year, with CO₂ bubbling through them.

After a year’s exposure to the CO₂, analysis of the samples showed that were 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. Three key factors — solid-phase metal mobility, carbonate buffering capacity and electron exchanges 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 CO₂ 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 concentrations increase within two weeks of exposure to CO₂,’ Jackson said.