In Pennsylvania, the release of fracking water has been banned in 2011, but traces from before the ban are still visible in aquatic environments.

Frack the environment

Hydraulic fracturing (or fracking) is a process through which oil companies can retrieve otherwise inaccessible reserves of shale gas. As the name suggests, it involves using a high-pressure mixture of water and chemicals (called fracking fluid) to create a system of fractures which would allow the gas to escape towards the surface, where it can be captured.

Illustration of hydraulic fracturing and related activities. Image credits: US Environmental Protection Agency.

Fracking is controversial for several reasons. It uses massive quantities of water, it appears to cause increased seismicity, and, of course, the leaks. Creating a system of fissures a few kilometers beneath ground is challenging, but ensuring that the system is tight and doesn’t allow leaks is massively more difficult. Naturally, many people are concerned that the fracking fluid or the gas itself can leak towards the surface, seeping into the soil and water reserves — which has observed to be the case at some wells in the past.

But the release of used fracking water is also a major issue with long-lasting consequences.

“Freshwater pollution is a major concern for both ecological and human health,” said David Gillikin, professor of geology at Union College and co-author of a new study. “Developing ways to retroactively document this pollution is important to shed light on what’s happening in our streams.”

In their new paper, Gillikin and colleagues report finding high concentrations of strontium, an element associated with oil and gas wastewaters, in the shells of freshwater mussels downstream from fracking wastewater disposal sites.

A smoking gun

Image credits: Engbretson Eric, USFWS.

In a way, freshwater mussels are a bit like trees — they can offer a lot of information about the environmental quality of the water they live in, much like tree rings offer information about past climate events. Because they feed by filtering water, mussels hold a record of past water quality, which can be studied.

“Freshwater mussels filter water and when they grow a hard shell, the shell material records some of the water quality with time,” said Nathaniel Warner, assistant professor of environmental engineering at Penn State. “Like tree rings, you can count back the seasons and the years in their shell and get a good idea of the quality and chemical composition of the water during specific periods of time.”

After usage, fracking fluid is treated and cleaned — but this process is not perfect. In 2011, biologists noticed that despite this treatment, water and sediment downstream from fracking wastewater disposal sites still contained worrying amounts of fracking chemicals. The water was contaminated and in turn, affected aquatic life, causing widespread damage. After this was revealed, Pennsylvania banned all fracking wastewater treatment facilities from releasing the water back into the ecosystem. But the effect of the released water before the ban is still unclear.

To shed some light on it, researchers collected freshwater mussels from the Alleghany River, both upstream and downstream of a wastewater disposal facility in Warren, Pennsylvania. They also collected mussels from two other rivers — the Juniata and Delaware — that had no reported history of oil and gas discharge, for comparison.

They particularly looked at strontium isotopes, which in this context can be a smoking gun for fracking wastewater. They also analyzed the oxygen isotope, to identify the year and season. Not surprisingly, they found elevated concentrations of strontium in the shells of the freshwater mussels collected downstream of the facility, whereas all others showed no significant elevation. But not everything came as expected.

Despite the 2011 ban, strontium levels didn’t immediately drop sharply. Instead, it took a while before the decrease was visible, and the decrease was quite slow. This suggests that even years in which fracking water has not been released back into the ecosystem, the effects are still visible.

“We know that Marcellus development has impacted sediments downstream for tens of kilometers,” said Warner. “And it appears it still could be impacted for a long period of time. The short timeframe that we permitted the discharge of these wastes might leave a long legacy.”

Considering the large scale of modern fracking, this is particularly concerning. According to the U.S. Department of Energy, up to 95% of new wells drilled today are hydraulically fractured.

“The wells are getting bigger, and they’re using more water, and they’re producing more wastewater, and that water has got to go somewhere,” said Warner. “Making the proper choices about how to manage that water is going to be pretty vital.”

This study goes on to show that even a few years of the process could have long-lasting, damaging consequences. It also suggests that freshwater mussels can be used to study potential seepages at oil sites, since conventional oil drilling can also cause a similar type of pollution.

Journal Reference: Thomas J. Geeza, David P. Gillikin, Bonnie McDevitt, Katherine Van Sice, Nathaniel R. Warner. Accumulation of Marcellus Formation Oil and Gas Wastewater Metals in Freshwater Mussel Shells. Environmental Science & Technology, 2018; 52 (18): 10883 DOI: 10.1021/acs.est.8b02727