Two recent papers have asserted the connection between fracking and radioactivity in wastewater. Khai Trung Le reports.
The radioactivity in hydraulic fracturing wastewater has been categorised in two papers from Dartmouth College, USA, noting the interaction between the chemical slurry and ancient shale during the fracking process. This follows a prolonged dispute in Pennsylvania regarding high levels of radium (Ra) found in surface waters for several years.
Both papers in the series, Rapid desorption of radium isotopes from black shale during hydraulic fracturing, published in Chemical Geology, focus on the Marcellus Shale, a geological formation in northeastern USA and the largest natural gas field in the USA. The first paper details how radium is leached into saline water hours after contact with the rock. This is from two sources – clay minerals that transfer 228Ra, and an organic phase that is the source of 226Ra.
The paper notes that ‘hydraulic fracturing of the Marcellus Shale produces wastewaters that are hypersaline and highly enriched in isotopes of radium. Radium is understood to derive from the Marcellus Shale itself, but its source phase and contribution to wasterwater production has not been described’.
The second paper details the radium transfer mechanisms, and attributes the extreme salinity and radium in wastewaters ‘to the progressive, hydrologic enrichment of injected fluids during hydraulic fracturing’.
The Dartmouth team stressed that investigating the interaction between water and rock kilometres below land surface levels has been extremely difficult. Prior to the study, the team was unsure whether the radium came directly from the shale or from brines found at depth across the Marcellus Shale. However, the team states its research confirms that as wastewater travels through the fracture network and returns to the drill hole, it becomes enriched in salts. This saline composition extracts radium from the shale, bringing it to the surface.
The first paper continues, ‘Experimental results and wastewater data together provide a coherent picture, that the distinct Ra isotopic signature of Marcellus wastewaters results from contemporaneous water-rock interactions that promote desoption of 226Ra from organics during hydraulic fracturing’.
In a comment to Materials World, Mukul Sharma, Professor of Earth Sciences at Dartmouth College, said, ‘The stuff that comes out when you frack is extremely salty. The question, is how did the waste become radioactive? […] Radium is sitting on mineral and organic surfaces within the fracking site waiting to be dislodged. When water with the right salinity comes by, it takes on the radioactivity and transports it.’
The long half-life
While all minerals have a degree of radioactivity, the Marcellus Shale is an unusually radioactive underground formation. In 2009, on analysing 13 samples of wastewater, the New York Department of Environmental Conservation found levels of radium as high as 267 times the limit safe to discharge into the environment, and several thousands of times above the limit safe for people to drink. during hydraulic fracturing.
Avner Vengosh, Professor of Earth and Ocean Sciences at Duke University, USA, told PRI in 2014, ‘Radium is very similar to calcium. As a result, it would accumulate in the bone, [eventually] leading to bone cancer.’ Vengosh found radium at 200 times the background level in a stream near one wastewater processing plant in Pennsylvania.
A joint study in 2017 between Pennsylvania State University, Colorado State University, USA, and Dartmouth found elevated levels of radium and nonylphenol ethoxylates in sediments from Conemagh River Lake. The highest concentration of pollutants was found in lake sediment layers deposited between 2008–2014, with the highest levels of radium found 19km downstream from treatment plants.
Similarly, seven years after Pennsylvania officials requested restricting the disposal of radium-laden fracking wastewater into surface waters, Duke University, USA, found in January 2018 that high levels of radioactivity persisted in stream sediments at three disposal sites. However, Vengosh also wanted to stress that fracking was not a sole offender. He said, ‘It’s not only fracking fluids that pose a risk. Produced water from conventional oil and gas wells also contain high levels of radium. Disposal of this wastewater causes an accumulation of radium on the stream sediments that decays over time and converts into other radioactive elements.’
You can read Rapid desorption of radium isotopes from black shale during hydraulic fracturing. 1. Source phases that control the release of Ra from Marcellus Shale at bit.ly/2QGnoBh
The second paper, 2. A model reconciling radium extraction with Marcellus wastewater production, can also be read at bit.ly/2C9muJR