Fracking chemicals: Organic screening

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  • Published: Jul 15, 2015
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
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Organic screening

An organic screening framework has been used to identify organic components of hydraulic fracturing fluid that have potential groundwater risks associated with their use. Of 659 different substances examined researchers identified 15 that could be problematic. (Image: Fracking head: Joshua Doubek; Thumbnail fracking site aerial view: Simon Fraser University)

An organic screening framework has been used to identify organic components of hydraulic fracturing fluid that have potential groundwater risks associated with their use in the event of a spill. Of 659 different substances examined, researchers identified just 15 that could be problematic based on their toxicity, mobility, persistence and how frequently they are used in "fracking".

Researchers at the University of Colorado Boulder predicts that 41 of the 659 organic compounds screened would persist at 10 percent or more of their initial concentrations to a transport distance of approximately 100 metres. That distance is referred to as the average state "setback" distance allowed in the USA between a fracking well and a drinking water source, explains principal investigator on the project, Joseph Ryan.

Fracking chemicals

Hydraulic fracturing is commonly known as fracking and has been the source of much controversy since it was first mooted as a way to access otherwise inaccessible subterranean oil and gas . It involves injecting a mixture of water, sand and various chemicals into a well under high pressure. A wide variety of chemicals are used at different levels to increase the viscosity of the fracking liquid overall, to inhibit equipment corrosion and to reduce friction between moving components of the machineryThis cracks the rock beneath the surface opening up fissures in the subterranean shale layers that then release natural gas and oil. The companies involved demand that the process is safe when carried out properly, but environmental concerns abound, especially when evidence emerges showing contamination of drinking water wells.

The Boulder team screened 659 compounds which are mostly cited in the nationwide FracFocus Chemical Disclosure Registry. This database is used by many states and companies must disclose chemical information about the ingredients they use in their fracking liquids at individual wells. 41 compounds were predicted to have at least 10% or more of their initial concentration remaining at the transport distance. 15 of those were identified on at least 50 FracFocus reports. The remaining 26 were identified on fewer than 50 of the FracFocus reports.Co-author and doctoral student in civil, environmental and architectural engineering, Jessica Rogers, adds that the remaining 26 compounds predicted to be mobile and persistent were very rarely used and only listed at fewer than 50 of the 50 000 FracFocus reports.

"We wanted to evaluate which compounds we should be paying attention to based not just on toxicity but also on the extent a particular compound travels from one place to another through groundwater," explains Ryan. "We found 41 compounds that were considered mobile and persistent, and a handful of those we would not want in our drinking water."

"There were two main objectives with this project," explains Rogers. "The first was to develop a screening process that could be used by researchers or others to prioritize organic fracking compounds based on how mobile and persistent they are in groundwater. The second was to use the framework to perform an initial screening based on currently available knowledge on the compounds identified in fracturing fluid by FracFocus."

The team's screening process involved using known degradation rates for specific organic compounds as they might be transported horizontally from the point of release, from a failed well casing to a drinking water well, for instance. Chemical structure and stability of each organic compound as well as its behaviour in water were all taken into account in the calculations. The team also used a wastewater treatment process simulator called BIOWIN 4 to help estimate the biodegradation of the organic compounds over time. The team used two transport scenarios - a highly porous aquifer with relatively high groundwater velocity and a less porous aquifer with a lower velocity. The compounds were evaluated for possible toxicity using the US National Primary Drinking Water Regulations and Health Assessment Information.

Consistent framework

The finding that so few of the many chemicals used have an increased mobility of exposure should there be an accidental spill and some of those compounds are used only very rarely in the first place might go some way to allaying many of the public fears surrounding the fracking industry, Ryan suggests. Hundreds of chemicals are used but very few are of significant concern. Nevertheless, some of those compounds could result in potentially hazardous exposures following spills or well failures, he says. Of the 15 compounds found to be putatively problematic, only two of them - naphthalene and 2-butyoxyethanol - were mentioned in more than 1 in 5 of the 50000 FracFocus reports. Only four of the compounds were identified on more than 5 percent of the reports.

"Just because a compound has been put into the ground doesn't mean it is going to migrate to a place where humans will be exposed to it," adds Ryan. "On the other hand, problems with particular compounds in groundwater could take a decade or so to even show up. We don't know enough about some of these processes right now."

The work addresses a repeated complaint from environmental groups who are frustrated by the FracFocus registry, which cites information on a well-by-well basis and only in a document format from which it is difficult to extract the large amounts of data in a usable form.

"We found out that pulling out data we needed, like how frequently a particular compound was used in hydraulic fracturing in wells across the country, was not so easy to do," Ryan points out. "But to evaluate mobility and persistence, we used existing tools so that others follow the same approach for looking at other organic compounds of interest." The next step will be to look at the breakdown products of these chemicals as well as upward vertical transport. "Currently, we don't have enough information on these processes to account for them consistently in our screening framework, but the science is rapidly evolving," Rogers adds.

"The next step with this research will be to experimentally determine fate and transport parameters for the compounds of concern so that we can improve our understanding of how these compounds behave in groundwater," Rogers told SpectroscopyNOW. "Another important research task will be to conduct a similar screening of compounds identified in flowback or produced water to identify any compounds of concern," she adds. "The framework could be used to guide groundwater sampling to measure compounds that are more mobile and persistent, and therefore more likely to be transported through groundwater. This screening framework helps researchers prioritize compounds for further study, and could also be used in designing more 'green' fracturing fluids," Rogers concludes.

Related Links

Environ Sci Tech Lett 2015, 2, 158-164: "A Framework for Identifying Organic Compounds of Concern in Hydraulic Fracturing Fluids Based on Their Mobility and Persistence in Groundwater"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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