Matrix Complications in the Determination of Radium Levels in Hydraulic Fracturing Flowback Water from Marcellus Shale

The rapid proliferation of horizontal drilling and hydraulic fracturing for natural gas mining has raised concerns about the potential for adverse environmental impacts. One specific concern is the radioactivity content of associated “flowback” wastewater (FBW), which is enhanced with respect to naturally occurring radium (Ra) isotopes. Thus, development and validation of effective methods for analysis of Ra in FBW are critical to appropriate regulatory and safety decision making. Recent government documents have suggested the use of EPA method 903.0 for isotopic Ra determinations. This method has been used effectively to determine Ra levels in drinking water for decades. However, analysis of FBW by this method is questionable because of the remarkably high ionic strength and dissolved solid content observed, particularly in FBW from the Marcellus Shale region. These observations led us to investigate the utility of several common Ra analysis methods using a representative Marcellus Shale FBW sample. Methods examined included wet chemical approaches, such as EPA method 903.0, manganese dioxide (MnO₂) preconcentration, and 3M Empore RAD radium disks, and direct measurement techniques such as radon (Rn) emanation and high-purity germanium (HPGe) gamma spectroscopy. Nondestructive HPGe and emanation techniques were effective in determining Ra levels, while wet chemical techniques recovered as little as 1% of ²²⁶Ra in the FBW sample studied. Our results question the reliability of wet chemical techniques for the determination of Ra content in Marcellus Shale FBW (because of the remarkably high ionic strength) and suggest that nondestructive approaches are most appropriate for these analyses. For FBW samples with a very high Ra content, large dilutions may allow the use of wet chemical techniques, but detection limit objectives must be considered.