Methane in the Water Part I: Toxicity
In recent weeks, there have been many reports in both the local and national media regarding a study published by Duke University showing elevated methane levels in drinking water wells located near fracking operations in New York and Pennsylvania. In my opinion, these reports do not provide sufficient information for the reader/viewer/listener to evaluate the fundamental question, “How worried should I be?” In this two-part series, I will attempt to provide a comprehensive answer to that question. To do so, I am going to have to delve a bit deeper into technical details than normal. However, with fracking coming to the Tar Heel State, I think it is important for this issue to be addressed accurately and comprehensively. So pour yourself a fresh cup of coffee and let’s get to it.
Let me start with a one-paragraph primer on fracking. First, a drilling company locates an underground deposit of natural gas, which is a mixture composed primarily of methane along with small amounts of ethane, propane, and butane. Next, the company drills down to the depth of the gas deposit and protects the well bore with steel piping encased in a layer of concrete. From the bottom of the vertical well, horizontal holes are drilled in several directions. Then a high-pressure slurry of water, sand, and chemicals is pumped into the horizontal holes, fracturing adjacent rocks. Fracturing the rocks allows the natural gas in the deposit to migrate to the vertical well bore, and subsequently to be brought up to the surface. Many of the chemicals used in the fracking process are highly toxic. (1)
As we consider the issues discussed below, an appreciation for depth will be helpful. Water wells for drinking and agriculture are almost always less than 1,000 feet deep, because that is where the water is. Fracking wells tend to be much deeper, 2,000 to 20,000 feet, because that is where the natural gas is. The separation in depth between underground aquifers and fracking operations is a critical parameter in trying to avoid water contamination. If fracking occurs at depths which are too close to aquifers, then cracks can extend from the fracking zone into the aquifer and allow fracking chemicals to contaminate the water. I have previously written about a case of this occurring in Wyoming. The physics of fracking suggest, at least to me, that the separation in depth between an aquifer and any fracking activity should be at least 1,000 feet.
The graph above, from the Duke University study, shows methane concentrations for water wells as a function of distance from fracking operations. The data clearly show that water wells closer to fracking operations have higher concentrations of methane. This graph contains a lot of information and implications, and, thus, raises a number of questions which I will attempt to answer below.
What is the source of the methane?
The two most common sources of methane in ground water are bacteria in the soil and natural gas deposits. Drilling companies frequently raise the possibility of multiple possible sources in order to suggest that methane found in ground water may not be related to their activities. However, it is actually quite easy to determine the origin of methane found in a water well. When bacteria are going about their business, they make methane and only methane. In contrast, methane from natural gas, which is produced by the decomposition of ancient organic matter deep underground, is accompanied by other decomposition products such as ethane, propane, and butane. Since the water in the wells from the Duke study contains these other hydrocarbons along with methane, there is little doubt that the methane they found was from natural gas.
Did the methane reach the underground aquifers due to fracking?
As you look at the graph above, the answer seems to obviously be “yes.” However, drilling companies have claimed that the methane may have infiltrated local aquifers prior to the fracking operations and that since the Duke study does not have baseline data collected prior to drilling, causation has not been established.
While the assertions from the drilling companies are defensible on the surface, they don’t stand up to scrutiny. Consider that all of the water wells in the Duke study are over the same shale formation that bridges the New York/Pennsylvania border. If methane in that zone was naturally migrating into the aquifers, one would expect that nearly all of the wells would be contaminated. To accept the drilling companies’ explanation that their activities are not related to the water contamination, one would also have to accept that somehow they have only drilled near to previously contaminated aquifers and that the aquifers in areas where they have yet to drill have somehow avoided the onslaught of naturally migrating methane. The odds of the drilling companies’ theories being correct are infinitesimally small.
The explanation posited by the Duke researchers is that methane is reaching the aquifers adjacent to the fracking wells by leaking through cracks in steel piping and concrete casings around the vertical well bores. I find this explanation to be far more compelling.
Is methane toxic?
The short answer is no. Methane is essentially inert and will not undergo chemical reactions except at very high temperatures. Therefore, any methane dissolved in water that you drink will pass through your body without causing any harm. Further, as flatulence can contain up to 10% of it, methane is not unfamiliar to your gastrointestinal system.
Is methane a harbinger of other pollutants?
The essence of this question is, “If methane can migrate from the fracking zone to the aquifer, can harmful fracking chemicals such as benzene do so as well?” To explain why the answer to this question is “not necessarily,” we need to talk a little chemistry.
Methane consists of a single carbon atom in the middle attached to four hydrogen atoms. Since the four hydrogen atoms are arranged symmetrically, methane is non-polar. What this means is that the electrons within a methane molecule are evenly distributed, which results in the characteristic that methane molecules tend not to stick to each other or to anything else. Methane is also a very small molecule. Since it is small and doesn’t stick to anything, methane can worm its way through very small cracks and fissures.
Molecules which are polar have a much more difficult time migrating from place to place underground. As an example, let’s consider water (H20), a molecule about the same size as methane. In the case of water, the two hydrogens are not symmetrically arrayed around the central oxygen atom. As a result, part of a water molecule is electron rich while the remainder is electron deficient. This has the effect of making water molecules act like little magnets such that they stick to each other and many other things, like soil and rock. So it has a much harder time migrating underground.
The chemicals used in the fracking process are both much larger than methane and tend to be polar like water, limiting their ability to migrate. Therefore, the fact that an aquifer has been infiltrated by methane is not a particularly strong indicator that fracking chemicals will soon arrive.
To sum up Part I, what we know so far is:
- fracking operations allow methane from natural gas deposits to reach drinking water aquifers;
- methane itself is not toxic; and
- methane in the water does not necessarily mean that other fracking chemicals will also contaminate aquifers.
Next week in the conclusion of this series, I will discuss other potential hazards of methane contamination of water wells, particularly fires and explosions.
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(1) Although the North Carolina General Assembly recently voted to make it illegal for a citizen of the Tar Heel State to disclose the identity of chemicals used in fracking here in the southern part of heaven, as I explained in Fracking Gag Rule Part I, everyone already knows what they are.