Duke researchers publish new paper on gas-drilling waste
Duke University researchers say they’ve documented elevated levels of a radioactive element where a western Pennsylvania waste plant discharged treated water previously used in natural-gas drilling.
Published Wednesday in the journal Environmental Science & Technology, the findings came from a team led by Nicholas School of the Environment professors Avner Vengosh and Rob Jackson.
The key finding, of elevated levels of radium in streambed sediments just below the plant’s discharge point, came even though it was clear that the treated water leaving the plant met the industrial discharge limit for radioactivity, the paper said.
The effluent nonetheless has a “significant impact” on the sediments. To wit, “most of the radium appears to be absorbed and retained in them” instead of flowing downstream, the paper said.
And the resulting concentrations are high enough that if the sediments themselves were treated, regulations “would require you to take them a licensed radioactive-waste facility,” Jackson said.
The team also found that the plant’s discharge appeared to contribute to elevated levels of salts in the stream’s water downstream of the facility, despite the diluting effect of the stream’s much larger flow.
It warned that one of the salts it observed, a variant of the element bromine, can complicate life for downstream drinking-water treatment plants, potentially by inducing the formation of treatment byproducts suspected of causing cancer.
The paper was the latest from Nicholas School researchers who are interested in the environmental effects of gas drilling that using hydraulic fracturing – “fracking,” to use the popular term – to break up subsurface rocks.
Like all other forms of oil and gas drilling, fracturing uses water and thus generates wastewater that has to be recycled, treated or disposed of.
Besides whatever additives drillers may place in it, the water picks up contaminants from the subsurface rock itself – salts mostly, but sometimes also the heavier, more radioactive elements that help fuel the Earth’s internal heat.
The precise mix will vary with the geology of the area being drilled.
Fracking is a major issue in North Carolina because geologists think there are a few potential gas fields in the state that the drilling technique can open up. The key areas are in counties south of the Triangle.
Officials at the N.C. Department of Environment and Natural Resources and the N.C. Mining and Energy Commission are crafting regulations for drillers to follow.
Waste-management rules are still a work in progress, but the mining commission last month produced a white paper that said “treatment for some end use such as surface discharge” is what it likely will suggest for any leftover drilling water that isn’t recycled.
Recycled drilling water is returned to a drilling operation for reuse.
The mining commission white paper said water injected into and removed from North Carolina’s gas-bearing rocks is “expected to have relatively low salinity” compared to what comes out of the ground in western Pennsylvania.
That means water recycled for use in additional drilling “ought to require minimal treatment,” and leftover water treated and discharged “ought to have a relatively low [processing] cost.”
The commission paper acknowledged that its preferred treatment option – “reverse osmosis,” a different technology than the one used at the Pennsylvania plant Duke’s researchers studied – would ultimately produce some solids that would also have to be disposed of.
It was silent on the question of radioactive byproducts.