Hydraulic fracturing -- the technique used on this gas pad in Pennsylvania -- involves lots of water. And that water comes in three varieties: fracking fluid, flowback water, and produced water. Is any of it safe?
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Hydraulic fracturing -- the technique used on this gas pad in Pennsylvania -- involves lots of water. And that water comes in three varieties: fracking fluid, flowback water, and produced water. Is any of it safe?
Hydraulic fracturing -- the technique used on this gas pad in Pennsylvania -- involves lots of water. And that water comes in three varieties: fracking fluid, flowback water, and produced water. Is any of it safe?

Natural Gas, Hydrofracking and Safety: The Three Faces of Fracking Water

When it comes to water from hydrofracking, the question of safety is murky at best.

The Chemical Cocktail of Fracking Fluid

For many folks the big baddie of hydraulic fracturing, also called hydrofracking or fracking, is fracking fluid — the mixture of water, sand, and chemicals that’s injected deep below the surface to fracture the rock and liberate the natural gas. A typical fracking operation uses between one and eight million gallons of water — that’s as much as 12 Olympic-sized pools. In addition to the water the mixture contains a proppant (typically sand) and a mix of chemicals drawn from a list of more than 700 [pdf]. These chemicals generally make up only about 0.5 percent of the total volume (though estimates differ — see here [pdf] and here), but assuming a total of four million gallons of water were injected into a well, that would translate into about 20,000 gallons of chemicals.

So, is fracking fluid really bad news? Maybe, maybe not. A lot of the chemicals are harmless — instant coffee and walnut hulls, for example (yum!). But others are not so benign. Among the hundreds of chemicals used in the thousands of different formulations, 29 are either “known or possible human carcinogens, regulated under the Safe Drinking Water Act for their risks to human health, or listed as hazardous air pollutants under the Clean Air Act” [pdf].

Even so, many argue that the stuff may not be that bad — the fluid is injected well below the surface and unlikely to migrate to aquifers and surface water. They may have a point. A recent study by a Duke team — with an admittedly large caveat because it “did not test comprehensively for organics or other potential additives in fracking fluids” — found no evidence of fracking fluids in drinking water near well sites — although they did find methane contamination. The Environmental Protection Agency, however, as reported in the New York Times, has investigated at least one documented case of fracking fluid contamination. 

Whatever problem fracking fluid might have posed in the past may become moot, as gas-drilling companies become more transparent and clean up their act. But even Halliburton’s newly formulated not-quite-“edible”-but-apparently-safe-to-drink fracking fluid doesn’t mean that all is hunky-dory in fracking water land. Why? Because there’s also flowback water and produced water.

Flowback Water

After water is introduced during the fracking stage, a portion of that is returned to the surface over the next days and weeks. The volume of this flowback water can range from as little as 10 percent [pdf] to as much as 100 percent of the fracking fluid. Initially, its composition resembles that of the injected fracking fluids, but as its residence time increases, its chemistry transitions to the composition of formation water found naturally within the shale, and once this change occurs, this water is called produced.

Produced Water

For a typical well, daily produced water volumes range [pdf] from about 80 to 1,200 gallons and are generated in tandem with shale gas over the well’s life. A lot of water and a lot of potential problems. Its composition is determined by the chemistry of the shale from whence it came. If there are toxic elements in the formation, there are likely to be toxic elements in the produced water.

Avner Vengosh, my colleague here at Duke’s Nicholas School, and his research group have been spending time in Pennsylvania gathering inorganic data specific to the Marcellus Formation. The table below shows some of their preliminary data for selected compounds collected over the first 20 days of a well operation. (Learn more about the study and its findings in this video.)

Compound Concentration


Drinking water limit (ppm)* Surface water criteria***
(ppm) Comments Chloride 40,000-70,000 250** 230 For comparison sea water has an average concentration of 19,000 Strontium 1,000, -2,300 n/a n/a   Barium 300- 2,500 2 n/a   Boron

1, -25 5 n/a   Chromium 1.4-2.5 0.1 0.074, 0.011             Selenium 0.5-1.0 0.050 0.005   Lead 0.080-0.14 0.015 0.025   Arsenic 0.050-0.200 0.010 0.15   Radium-226 3,000-5,000 pCi/L 5 pCi/L   Ingesting radium-226 (a radionuclide) over many years can lead to an increased risk of cancer

As you can see, the produced water in Avner’s samples was highly saline with a number of toxic trace elements, which far exceeded (up to a 1,000 times) what’s found in both drinking water and surface water ecological criteria; it also contained radium, a radioactive element.

Where It Goes Is What You Need to Know

For fracking to be safe water-wise, you gotta dispose of flowback and produced water without allowing it to mix with surface or drinking water. One method is injecting the stuff in deep geologic formations — however, there’s some evidence that such practices may lead to earthquakes, albeit small ones. Recycling the water, which preserves the local water supply and helps minimize the amount that must be disposed of, can have its own drawbacks — recycling creates a highly concentrated sludge which is often unregulated and without proper disposal can pose a risk to drinking water.

More problematic is the transfer of wastewater to water treatment facilities, most of which are ill-equipped to deal with the toxics and will therefore pass them on into rivers and potentially downstream drinking water supplies. (See here, here and here.)

Most problematic of all is when flowback and produced water are spilled or the selected disposal method has the potential to impact drinking water aquifers or surface waters. How often does this happen? Data from Pennsylvania’s Department of Environmental Protection show that roughly 50 spills have occurred in the Marcellus through August of this year, some prompting evacuations and others shuttering operations.

Good rule of thumb: Drinking water and fracking water don’t mix. Let’s keep it that way.