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There's Methane in Your Drinking Water. So What?

Like so many controversial topics, it is hard to get good information on fracking. Participants from both sides of the debate are prone to exaggeration and cherry-picking. Pro-frackers pretend there is absolutely nothing to worry about, and anti-frackers pretend that tectonic plates will rip apart and the Earth will deflate. The truth is undoubtedly somewhere in the middle.

One of the main concerns is the presence of methane in drinking water. Infamously (and dishonestly) portrayed in the "documentary" Gasland, a guy in Colorado lights his tap water on fire. Gasp! It must be because of fracking. But it wasn't. The methane in his tap water seeped there naturally by a process called methane migration. (Perhaps Gasland Part II will correct the record.)

methaneinwater.jpgAlas, a new study in PNAS shows that, indeed, fracking can increase the amount of methane in your drinking water. Scientifically dubious activist websites, such as Desmogblog, are already touting the study as a "damning" indictment against fracking. Is it?

The authors sampled well water and plotted the amount of methane in the water (y-axis) as a function of the distance in kilometers (x-axis) from a gas well. (See chart.) As shown, the closer a well is to a fracking site, the more likely it is to have a higher methane concentration.

Should this worry us? Not really. Most wells had methane levels that were far below the "action level" recommended by the US Department of the Interior. And, as just mentioned, methane naturally contaminates groundwater all the time.

Besides, there's another big point to consider, and almost nobody ever does: What level of methane contamination is actually dangerous?

Methane is non-toxic, but it is explosive. And, at very high concentrations, it can cause death by asphyxiation (since there isn't enough oxygen to get to your lungs). In the chart, the worst sample had 70 mg of methane per liter of drinking water. Can we expect the residents in this house to choke and then explode in a huge burning ball of flames?

No.

Using a little chemistry and some simplifying assumptions, a fairly basic calculation can be performed. First, we need to know what percentage of the air in their house would contain methane. For the sake of argument, let's assume the worst: All 70 mg of methane (CH4) per liter of water escape into the air. And, the average American family of four uses 400 gallons (1514 L) of water per day.

70 mg  x  1514 L = 105,980 mg = 106 g CH4      
1 L                                                                         

So, 106 grams of methane escapes into the air. But, what volume is that? For sake of simplicity, let's assume standard temperature and pressure which allows us to easily calculate how much volume 106 g CH4 takes up.

106 g CH4  x  1 mole  x  22.4 L  =  148 L
       16.04 g     1 mol

At the end of a day, about 148 liters of methane has escaped into the house. That sounds like a lot. But what percentage of the air in the house is now made up of methane?

That depends on how big your house is. The average new American home is 2,480 square feet. But, the average home in 1973 was 1,660 square feet. Let's do a conservative estimate of 1500 sq ft. And we'll assume a 10-foot-tall ceiling. What's the volume of the house?

1500 sq ft x 10 ft = 15,000 cubic feet = 424,753 L

Wow, that's a lot of air. To determine what percent is methane, all we do is divide:

148 L methane  =  0.035%
424,753 L air                   
             
At the end of a single day, assuming the house is airtight, 0.035% of the air will be composed of methane. That's not very much at all, and it's far, far below levels that would be considered dangerous. The lower explosive limit for methane is 5%, which means the air needs to be 5% methane before any explosions can occur. And asphyxiation won't happen until the air is 50% methane.

Now, one thing left out of the analysis is this: How much air inside the house is exchanged with the air outside on a daily basis? And, does methane escape more/less than other gases in the air? That would be tough to model, but if the residents were paranoid, they could always purchase a methane gas detector (which also detects propane and carbon monoxide).

But, most likely, the residents of the house will be perfectly fine. Anti-fracking scaremongering about methane in drinking water fails scrutiny from basic chemistry.

Source: Robert B. Jackson, Avner Vengosh, Thomas H. Darrah, Nathaniel R. Warner, Adrian Down, Robert J. Poreda, Stephen G. Osborn, Kaiguang Zhao, and Jonathan D. Karr. "Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction." PNAS June 24, 2013. doi: 10.1073/pnas.1221635110

(H/T: Special thanks to Rhett Allain and Hank Campbell for double-checking my calculations. But as I was only a chemistry minor, please don't blame them for my opinions or mistakes.)

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