Further to my musings a little under a week ago, I have been further investigating the geological viability of CCS. I ended my last post with a rosy outlook, suggesting that CCS really made sense from a geological viewpoint.
Further research
After some further reading I came across a study which refutes this viewpoint. Lawter et al. (2015) conducted an experiment into the effects of sequestering CO2 when a CO2 reservoir is overlain by an unconsolidated aquifer (poorly consolidated sedimentary rocks containing groundwater).
The study, conducted in the laboratory, found that some soluble elements, such as sodium, arsenic, magnesium, molybdenum and strontium, would leak into the aquifer if CO2 was injected.
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| Figure 1: From Lawter et al. 2015. Injection of CO2 into an aquifer causes a reduction in pH. This subsequently increases the mobility of many elements (see below). |
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| Figure 2: From Lawter et al. 2015. Increases in concentrations of toxic lead and arsenic, surpassing the safe levels defined by the EPA (US Environmental Protection Agency). These increases in concentration correlate with CO2 injection. |
Implications
These results are significant because elements such as arsenic and molybdenum are toxic. Should these elements enter the groundwater supply they would have the potential to threaten human life.
The paper is important in highlighting how element mobility can change after CO2 injection. However, I personally believe that with adequate prior research and knowledge, potentially dangerous CO2 sequestration sites can be avoided. This is a relatively simple and cheap process, this study by Bachu (2002) sets out the options for different CO2 sequestration sites.
I also approach the findings within the paper with some scepticism. This is because of the purely chemical nature of the experimentation. The paper doesn't take into account geological factors, such as explaining the pathway along which such contaminants would travel into the aquifer. As mentioned in my previous post, CCS generally takes place in the presence of an impermeable barrier between the sequestered CO2 and overlying sediments. The studies (e.g Chadwick et. al 2005) discussed in my previous post found that CO2 didn't leak into overlying aquifers when sequestered.
This research is undoubtedly a barrier to CCS development, rightly so, given the potential human impact. However, I believe that it is preventable with proper site choice and management. Because of this, I still believe that CCS makes geological sense.
Any idea if the amount of CO2 stored is great enough to make a lake nyos style event a possibility?
ReplyDeleteThanks
Hi there.
ReplyDeleteInteresting point, and one I hadn't really considered. Reading this report (http://shalegas-bg.eu/download/ccs/100106-Health-Risks-CCS.pdf) the Lake Nyos event released the same quantity of CO2 as produced at a coal fired power station over the course of a week.
Natural topographic troughs at Lake Nyos contributed to the events severity, however, given that only a weeks worth of CO2 was leaked, there is clearly a level of risk associated with long term CO2 storage at CCS sites - where months and years worth of CO2 is likely to be stored.
I can't find any studies associated with assessing this risk - I would be interested to see the safety measures in place for a leak at sites such as Boundary Dam. Obviously at a power station safety measures such as monitoring CO2 pipes etc. would reduce the risk, as would nearby evacuation plans.
However, you raise a valid point, and clearly any CCS facility would have to factor CO2 leakage into its safety plans.
Lewis