Although there continues to be a great deal of comment-worthy material about Fukushima (including the latest idiotic suggestion that a collapse of the spent fuel storage in Unit 4 might call for the evacuation of California) I’d like to take a bit of a break from the apparent never-ending story. Partly I’d like to cover topics other than Fukushima (although the continuing scientifically ill-informed silliness does make it a fertile field), partly because I need more time to research some of the Fukushima stories, and partly because, with winter upon us, it seems a good time to look at where an increasing amount of our natural gas comes from and whether or not it brings with it any radiological hazards. In this case, the question is whether or not fracking (hydraulic fracturing) releases the torrents of radon that many claim it does. But first, a little background.
Where the gas and radon come from
Life first appeared on Earth about four billion years ago and as soon as it appeared organisms began to die and they drifted to the bottom of whatever sea they lived in where they were covered with silt and clay. Over time these accumulated to form sizeable deposits; over a longer time they became deeply buried. The Earth’s geothermal gradient is about 25˚ C per km of depth (away from the margins of tectonic plates and away from hot spots); bury something deeply enough and it begins to cook. Heat up organic material to about 100˚ C (equivalent to burial to 4 km), subject it to high pressures, and cook for a few tens of millions of years and the rocks start to fill with natural gas. Petroleum forms at lower temperatures; heat the rock too high and the hydrocarbons are cooked away altogether. Also contained in the rock are huge quantities of brine; water from the ancestral sea in which the original organisms grew and died.
So that’s where the gas comes from; the next part of the question is how the radioactivity gets into the gas. And this part is pretty interesting.
Uranium chemistry is about as complex as any of the natural elements – one aspect is that uranium, while soluble in oxygen-saturated water, is insoluble in waters that lack oxygen. During the first few billion years of Earth’s history the Earth’s atmosphere was largely anoxic and uranium was fairly immobile in the environment; after that time oxygen began to build up in the atmosphere and to dissolve into the seawater. At about this time uranium began to mobilize and move through the environment. And when it entered regions that contained the decaying remains of the early organisms it precipitated out of solution. With time the uranium decayed, forming radioactive progeny which, themselves, decayed – after over a dozen such steps the uranium finally turned into stable lead. But it’s the intermediate steps that are important because they include radium and radon – over the eons, the natural gas deposit accumulated radioactivity and if we fast-forward to the present we find that virtually every natural gas deposit on the planet (oil and coal as well) contains radioactivity. Recovering natural gas not only liberates the gaseous radon contained in the oil, but radium and other radionuclides are also dissolved in the concentrated brine – they precipitate out of solution and contaminate the scale that lines natural gas pipelines and settles out as sludge in the holding tanks. And this is important to remember – every natural gas deposit contains this radioactivity, not only the gas recovered by fracking.
Radon in the Marcellus Shale
Getting gas out of a formation is not as easy as just drilling a hole and letting it flow – if the rock is porous then this will happen, but many rocks just aren’t all that porous, and shale is a particularly “tight” rock. But a huge percentage of natural gas formed in rocks that derived from the mud and silt that covered the ancient organisms – sediments that formed fairly impermeable shale. To get appreciable amounts of gas from these tight deposits we have to find a way to break them up – by forcing fluid in under high pressures and by forcing sand into the formation as well to prop open the cracks formed by the high-pressure fluids. This particular posting is not the place to discuss all of the issues of this controversial topic – all that I’ll tackle is the question of radon.
Among the concerns raised by drilling into shale for natural gas recovery is the concern about radon entering the natural gas. As I mentioned above, there’s radon in all natural gas so the question isn’t so much whether or not there’s radon in the gas so much as is there more radon in gas that originates in shale formations than there is in other natural gas and, if so, whether or not this poses a health risk. In January 2012 a report authored by anti-nuclear activist Marvin Resnikoff suggested that using natural gas from the Marcellus Shale (a rock formation that extends through much of New York and Pennsylvania) would release enough radon to cause tens of thousands of deaths annually. Resnikoff’s conclusions were refuted by a July 2012 report written by Lynn Anspaugh, a respected radiation scientist who has served on a large number of highly respected national and international radiation advisory bodies (a complete list is included in his resume which is appended to the report linked to above).
The crux of Resnikoff’s argument is his claim that natural gas from the Marcellus shale is extraordinarily rich in radon, that this radon will be incorporated in the gas when it reaches homes in New York City, and that this extra radiation exposure places New Yorkers at risk. Resnikoff calculated that there could be as many as 30,000 additional annual cancer deaths from this radiation exposure. But, having read Resnikoff’s report I have to say that I don’t place much credence in his conclusions. Here’s why.
Resnikoff makes three crucial errors in his report:
- He failed to actually measure radon concentrations in the natural gas at any point from the wellhead to the customer’s home. Instead he relied on a series of calculations based on shaky information found in preliminary studies performed a number of years ago.
- He vastly over-estimates the amount of radon in the Marcellus Shale natural gas in his report, compared to actual radon concentrations that have been measured.
- He overestimates the risk from exposure to low levels of radon, ignoring the advice of the EPA and of both national and international radiation advisory bodies.
Anspaugh points out that, in addition to these mistakes, Resnikoff’s calculations are based on a series of parameters for which he provided no basis – Resnikoff provides no reference for any of the values he uses, and neither does he account for the inevitable variability and uncertainty in these values. This is contrary to the normal scientific methodology. And, as Ansbaugh notes, Resnikoff also failed to make a single radon measurement that could have either supported or refuted his argument – he never measured the actual radon concentrations in either the natural gas supply or in the homes he was concerned about.
When radiation dose calculations are based on actual radon concentrations it turns out that the added radiation dose is trivial – on the order of a few tens of microSieverts (a few millirem) annually. It’s only when these trivial doses are multiplied by millions of people and extended over a lifetime that they seem to become significant. But this logic is flawed – ten million people exposed to 10 µSv annually (we are typically exposed to about 3000-4000 µSv annually from natural radiation) are no more likely to develop cancer than would ten million people who each have a 1-gram rock thrown at them. True – the cumulative dose might be 100 Sv (or 10 tons), which is certainly enough to cause harm. But what we’re interested in is the dose to the individual. Throw a small pebble at each of ten million people and you’ll have a bunch of irritated folks, but not a single crushing death in spite of the cumulative “dose.” Similarly, a dose of 10 µSv is a trivial dose of radiation no matter how many people receive it. According to the International Commission on Radiation Protection “Collective effective dose is not intended as a tool for epidemiological risk assessment, and it is inappropriate to use it in risk projections. The aggregation of very low individual doses over extended time periods is inappropriate, and in particular, the calculation of the number of cancer deaths based on collective effective doses from trivial individual doses should be avoided.” Resnikoff either ignored or was unaware of this guidance.
There are plenty of concerns about the use of hydraulic fracturing to extract natural gas from shale formations, just as there are plenty of reasons why this technique was developed and is being used. But the risk of radiation exposure to the users of this natural gas is a specious argument that tends to obscure, rather than to illuminate, this question.