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Following the recent post on the potential pitfalls of "Clean Coal," a new study out by Duke University shows that, in fact, if there ever is a "Clean Coal" solution to the dirty problem of the coal industry, it might face an even bigger obstacle. Says Dr. Bill Chameides, Dean of the Nicholas School of Earth & Ocean Sciences:

If you see a future for coal, it probably includes carbon capture and storage (CCS). There's lots of coal in the ground for the taking, but it is, if I may come clean about the stuff, the dirtiest of the fossil fuels. Burning coal generally leads to about 35 percent more carbon dioxide (CO2) emissions than burning petroleum and about twice as much (CO2) emissions as burning natural gas. That would suggest that coal does not figure into our low-carbon future.

Without CCS, an abundant and relatively cheap source of energy is off the table. And with coal off the table, powerful political groups -- the coal industry and coal workers -- are suddenly threatened by the march to a low-carbon economy. So, not surprisingly, there's a big push for CCS with the government providing incentives, subsidies, and research and development dollars.

Thus, he sets the stage for the real problem: what happens if the CCS process leads to carbon leaking into, say, an aquifer that lies above where the carbon is being injected underground?

There's the question of permanence -- will the CO2 leak out, and if it does, what happens then? It's this issue that was addressed in a new paper by Mark Little and Rob Jackson, my colleagues at Duke, and published last week in the journal Environmental Science & Technology.

Little and Jackson investigated what would happen if CO2 placed in a saline aquifer escaped into overlying groundwater. The premise for their study was the following:

1) While saline aquifers are excellent places to trap CO2, they are not perfect. Some escape of CO2 is probably inevitable (see graphic below); and

2) Some of that escaped CO2 would likely find its way into overlying freshwater aquifers used for drinking water, where it may make that drinking water ... well, undrinkable.

And the results of their study?

The authors gathered sediment samples from freshwater aquifers that lie above saline aquifers that could be used as CO2 storage sites. They then exposed these samples to water solutions with enhanced concentrations of dissolved CO2. The authors found that the samples with enhanced CO2 showed increased acidity, as would be expected because dissolved CO2 is a weak acid (i.e., carbonic acid).

But they also found that the enhanced acidity led to dissolution of metals such as uranium, cobalt, cadmium and iron. In some cases the concentrations of metals increased by two orders of magnitude and in some cases the increased concentrations exceeded the primary or secondary safe drinking-water standards, meaning these concentrations could pose a health risk and/or cause cosmetic effects (like skin discoloration) or aesthetic effects (like taste or odor).

Yikes! Skin discoloration and icky smelling water? Forget about it! NOT IN MY BACK YARD!! The NIMBY's will be out in fine fashion when these studies come percolating into the public realm, that's for sure.

Dr. Chameides is a little more calm about his conclusion:

The authors do not suggest that CCS should be abandoned as a result of their findings -- just that there should be careful monitoring of groundwater in areas where CO2 is being stored. Such monitoring would provide an "early detection of ... leaks" that could presumably lead to remedial action to prevent serious drinking water contamination. Quite reasonable but I suspect that Little and Jackson's results will provide fodder for the NIMBY opponents of CCS when the coal industry comes knocking on their door looking for storage sites. Like I said: the future of "clean" coal is murky.

Murky indeed.

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