Trace metal distribution and mobility in drill cuttings and produced waters from Marcellus Shale gas extraction: Uranium, arsenic, barium

Fingerprinting Marcellus Shale waste products from Pb isotope and trace metal perspectives

“…The DI and acid leaching techniques used in this study were successful in estimating the magnitude of the environmentally relevant element concentrations present within the Marcellus Shale, as concentration ranges for the Marcellus Shale from this study in many cases are similar to total concentration results from other black shale studies (Table 2). For the same set of drill cuttings used in this study Phan et al (2015) report U concentrations in the Marcellus Shale between 5 and 23 mg/kg, which are higher than the 1 and 11 mg/kg reported here, because the sequential extraction methods from Phan et al (2015) revealed the main reservoir for U was silicate residue. Methods used in this study did not mobilize all of the metals from the silicate residue, so the acid soluble metals reported from this study should be considered as amounts potentially available from the Marcellus Shale following surface weathering or subsurface drilling related processes.…”

“…There are similar concerns about quick release of U and its daughter products from unweathered Marcellus Shale waste products that have been investigated using sequential extraction techniques (Phan et al, 2015). Companies routinely use a U concentration proxy in the form of down hole gamma ray logging Overlying and underlying units plotted for reference, they had indistinguishable differences in Pb isotope ratios between unoxidized and oxidized samples.…”

“…A deionized (DI) water leach was used to identify elements available from leaching of cuttings in part to mimic rainfall impacts during surface storage in aerobic portions of landfills or elsewhere on the Earth's surface (Phan et al, 2015). A hydrochloric acid (HCl) leach was used to simulate metals released during the acid injection step during hydraulic fracturing, because 3-28% v/v HCl is commonly used to help dissolve minerals and initiate rock fractures (Earthworks, 2013;Frac Focus, 2013) during initial stages of hydraulic fracturing of the Marcellus Shale Soeder et al, 2014).…”

“…Similar weathering processes could release metals into the environment when Marcellus Shale waste material is disposed of at the Earth's surface (Jin et al, 2013). Sequential extraction techniques indicate the potential for mobilization of As, Ba, and U of Marcellus Shale cuttings in surface storage and landfill conditions, through carbonate dissolution and cation exchange (Phan et al, 2015); and Rn contamination is of concern for homeowners situated on Marcellus Shale bedrock, sourced from U decay within the Marcellus Shale (Hand and Banikowski, 1988).…”

Partitioning of naturally-occurring radionuclides (NORM) in Marcellus Shale produced fluids influenced by chemical matrix

“…1–9 Recent reports demonstrated that Marcellus Shale produced fluids from unconventional drilling are enriched in Ra isotopes ( 228 Ra, 226 Ra, 224 Ra) and devoid of most other long-lived NORM, such as certain U, Th, Pb and Po isotopes. 1,9–11 Despite research interest in radionuclides contained in Marcellus Shale produced fluids, there have been few laboratory-based studies that characterize the fundamental chemical behavior of NORM in Marcellus Shale produced fluids. Information has been gleaned about the chemical behavior of NORM in these fluids from environmental studies; however, even well designed environmental studies may not accurately characterize the chemical behavior of unconventional drilling wastes due to uncertainty and complexity of environmental sites in a region of the United States that has a long history with the extractive industries.…”