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Hydraulic fracturing, commonly called ‘fracking’, is a mining technique used to extract natural gas and oil from deep underground that involves drilling a well into bedrock, typically shale, and injecting high-pressure fluid. The fluid releases the target fossil fuels.
The fluid used in fracking contains about 85 percent water and 13 percent sand, which is used to open up cracks and release hydrocarbons. The rest of the fracking fluid is comprised of chemical components like friction and corrosion inhibitors.
After being injected, the fracking fluid reverses flow and much of it returns to the surface. Depending on the nature of the rock being mined, the ratio of fracking wastewater that returns is typically between 10 and 70 percent.
Wastewater generated from fracking includes salts (anions and cations), metals, and radioisotopes. This by-product is typically sequestered in injection wells, recycled in additional events or shipped to treatment facilities for remediation and discharge into surface waters.
As a result of health and ecological concerns, the various components of wastewater from fracking operations are monitored.
Types of Wastewater
There are two kinds of wastewater in fracking operations: flowback and produced. Flowback is the fluid that comes back to the surface after a fracking event, but before the well begins to yield fossil fuels. Produced fluid has come back to the surface after the well begins yielding hydrocarbons. While both kinds of liquid can contain materials that were in the rock layer, flowback water is mainly made up of fracking fluid.
Fracking wastewater is typically disposed into injection wells, reused or treated to remove salts and discharged to surface water. Disposal and transfer operations do involve the risk of accidental spills, which could affect surface water in the immediate area.
Both kinds of water release materials from deep underground. The salts, metals and radioisotopes that are released by fracking and captured by wastewater may endanger ground and surface waters, if not correctly handled. This presents a serious risk for drinking water sources.
By determining the amounts of anions and cations in flowback wastewater, operators can modify their desalination treatment plan, if the objective is to discharge into surface waters. Ion chromatography is typically used to test for inorganic salts found in flowback water, including bromate and chlorite. Two-dimensional ion chromatography may be used to explicitly test for bromate.
When testing fracking wastewater, samples may need to be treated to eliminate materials that may obstruct analysis. Fracking samples are often pre-treated to get rid of matrix interferences, like metals and hydrophobic compound, to expedite trace-level testing.
Given that fracking wastewater can have very high concentrations of analyte, it is often essential to use low testing volumes or dilute samples ahead of testing make certain that outcomes fall inside the calibration range of standard testing equipment.
Ion chromatography tends to be the preferred option for anion, cation and organic acid testing of wastewater. Two-dimensional ion chromatography offers greater selectivity of the analytes over matrix ions. Also, two-dimensional chromatography also allows for focusing on an analyte peak that may have been partly resolved in initial testing.
Environmental protection agencies in the United States have also used a radium-measurement process to evaluate for the radioactive composition of fracking wastewater. In the test, scientists add barium to a sample and then add sulfuric acid to precipitate out sulfate salts. By testing the radioactivity of precipitated solids, scientists can determine the quantity of radium present in wastewater.
Although this test is widely accepted, researchers from the University of Iowa reported in a 2014 study that a spectroscopy technique used to detect radon isotopes is a more robust test.
Sources and Further Reading