What the Frack?
Doc – what is it with fracking and radioactivity? I’ve seen a few things on the TV news about fracking and chemicals or natural gas leaking into drinking water – now I read in the NY Times that it’s putting radioactivity into the water as well. What’s going on here?
Interesting article – thanks for telling me about it! Not to mention that I grew up in Ohio, not far from the places they mentioned. Brings back fond memories! But that’s not really answering your questions, is it?
As I see it there are two main questions here:
- Is there extra radioactivity in the rocks that host petroleum and natural gas deposits and, if so, why?
- How is the radioactivity getting into the aquifer and is it harmful?
Let me start with the first question!
Is there extra radioactivity in the rocks that host petroleum and natural gas deposits and, if so, why?
I maybe discussed this earlier, but I’m having trouble finding it, so let’s start off with the aquatic geochemistry of uranium. And not to worry – aquatic Geochem is not one of my strong points so I’ll stick with what I understand, which ought to be enough for this part!
What it comes down to is that uranium dissolves nicely into water that’s loaded with oxygen, but not so much into water that’s oxygen-deprived (anoxic). So picture, if you will, rain falling from the skies (picking up oxygen as it descends through the atmosphere), running over exposed rocks (where the oxygen-rich water dissolves uranium that’s in some of the crystals making up the rock), and flowing through a series of rivulets, streams, brooks, and rivers until it flows into a swamp or into the ocean and percolates through seafloor sediments. Swamps and sediments collect organic matter – leaves, branches, roots, insects, the remains of algae, plankton, and other marine life – and when that material decays it does so with the assistance of the oxygen the water carries, removing oxygen from the water.
When oxygen levels are sufficiently low the uranium becomes insoluble, precipitating from solution and collecting in the muck. Over the ages the muck will become compressed, cooked by high temperatures deep underground, and the organic material will turn into petroleum and/or natural gas (depending on the temperatures and pressures to which it’s exposed) and these hydrocarbons and the waters of the former swamp will contain all the uranium that precipitated from solution so many millions of years in the past. Not only that, but U-238 decay gives rise to a decay series with 18 different radionuclides – over the course of a few million years these progeny nuclides accumulate, contributing radon (Rn-222), radium (Ra-226), and isotopes of lead (Pb-210), Bismuth (Bi-214), polonium (Po-210), and more. And U-235 also decays to stability, through a series of 15 radionuclides as it decays to stability. All of these radionuclides accumulate in the sediments and decaying organic material and in the residual water in which it was once dissolved, and they are all present in the hydrocarbons that form as this organic matter is “cooked” by the temperatures and pressures that result from its burial deep underground. And all are present millions of years later when these hydrocarbons are retrieved and brought back to the surface. This is where the radioactivity comes from.
How is the radioactivity getting into the aquifer and is it harmful?
The short answer here is pressure. Rocks that are deep underground are bearing the weight of hundreds or thousands of feet of the overlying rocks, as are the fluids they contain; pressures can be hundreds or thousands of pounds per square inch higher than the air pressure at the Earth’s surface. When drillers punch a hole through the overlying rock to access the hydrocarbons, the high pressure at depth can force the hydrocarbons up the borehole to shallower depths – this provided the pressure that formed “gushers” in the days before drillers learned to contain the fluids they were tapping into.
The thing is, even if fluids flowing up the borehole are contained, that pressure differential is felt on the outside of the drill pipe as well and if the holes are not properly sealed around the pipe the fluids can force their way to shallower depths along the outside of the pipe as well as through its center. If the borehole and drill string penetrate through aquifers these fluids and the radioactivity they contain can ascend into the aquifer(s) from which drinking and irrigation waters are drawn. If the high-pressure fluids can crack the rocks or force their way through fissures and fractures then it, and the radioactivity, can contaminate the aquifer.
As if that weren’t enough, many states (including Ohio) let oil companies dispose of the fluids their drilling brings to the surface by injecting them at high pressure back into the depths from which they came. But once underground, if the borehole isn’t adequately sealed, they can migrate back to shallower (and lower-pressure) levels.
A single U-238 atom will give rise to eight alpha-emitting and 6 or so beta-emitting progeny nuclides on its route to stability; U-235 has seven alpha-emitting and about the same number of beta-emitting nuclides in its own decay series. These will be present in the fluids at depth in varying concentrations depending on the geochemistry of each decay series nuclide. I haven’t been able to find the concentrations of alpha and beta radioactivity in the waters of southern Ohio, so I’m not sure if they exceed the levels permitted by the Environmental Protection Agency (5 pCi/L). If allowable levels are exceeded then drinking this water might be harmful but, even if radioactivity concentrations are lower than allowed the aquifer might still be contaminated with brines, metals, and other contaminants from ancient waters rising into the aquifer – not to mention the salt and other dissolved solids found in seawater now and in the deep past. And even if the drinking water is safe to drink, it doesn’t take much in the way of salt or dissolved minerals to turn water unpalatable – the residents are stuck with this regardless of the radioactivity that’s captured their attention and sparked their concerns. But at the moment, the matter seems to have fallen into the realm of political talking points – hopefully it will make its way back into the public health sector and nobody will get sick.
Given all of that, and accepting that I can’t find enough information to estimate a radiation dose (and, when it comes to health risks, dose is everything), here’s what I can say:
- While alpha radiation can be highly damaging if it’s ingested or inhaled, there’s got to be enough of it to give a dose high enough to put a person at risk; this isn’t easy to do, even with migration of alpha-bearing brines into the aquifer.
- But some alpha-emitters are what’s called “bone-seeking” radionuclides that collect in the bones, where they remain for decades – over time they can build up, delivering an ever-increasing dose to the person.
- And that dose depends on the amount of alpha activity that accumulates and the length of time it’s inside the body.
And I’m afraid that’s about all I can say about this, although I know it’s not very satisfying. Is there radioactivity in the aquifer? Sure seems to be the case. Is it harmful? Don’t know – and can’t tell unless I can find some information on the amount that people might be ingesting.