Rare Earth Element Signatures as Geochemical Forensic Tools
Presented on Monday, April 29, 2013
Clint W. Noack, David A. Dzombak, PhD, P.E. and Athanasios K. Karamalidis, PhD, Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA
Rare earth elements (REE), encompassing the lanthanides (La to Lu) and Yttrium, are in trace amounts throughout the earth’s crust, in only a small number of mineable minerals and scattered in geologic strata. Unique REE fractionation patterns have long served as petrogenetic and geochemical modeling tools. For example, the REE abundances and inter-element relationships have been employed to analyze regional groundwater mixing trends on the basis that different waters bear unique REE signatures. The objective of this study was to assess the potential use of REE signatures not only to detect contamination of a fresh groundwater, but also to determine the source of the contamination. Thus, REE signatures can serve as naturally occurring tracers of fluid transport during shale gas development and capable forensic tools for differentiating between sources of groundwater contamination.
A compilation of literature studies of REEs in waters of widely varying compositions was performed and the data was screened for statistical analysis. Analysis of similarity, a non-parametric, multi-variate statistical technique, was performed on this database to determine which water types display unique REE signatures. Based on the current dataset, analysis of similarity on REE abundance was inconclusive for several of the water types investigated. However, by using typical shale-normalized inter-element ratios the different water types are readily differentiated statistically. Additionally, the statistical power of these comparisons is independent of the reference material.
Similarly, a simplified, computational mixing experiment, using correlated multi-variate random number generation, was used to test the efficacy of changing REE profiles to detect contaminant intrusion into a fresh water aquifer for a variety of leakage rates and REE distributions. This improves previous REE-based mixing models by considering the uncertainty of REE distributions. For a continuously-monitored fresh water being polluted by an unknown contaminant source, even small leakages (≤0.1%) are detectable with high power.
Clint W. Noack
Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA
Clint W. Noack is a second-year graduate student at Carnegie Mellon University and a NETL-RUA Graduate Fellow studying the geochemistry of produced waters from the Marcellus shale during natural gas extraction, focusing on utilization of naturally occurring geochemical tracers. Previously, he explored opportunities for carbon sequestration via aqueous carbonation of alkaline industrial wastes.
David A. Dzombak, PhD, P.E.
Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA
David A. Dzombak is the Walter J. Blenko Sr. Professor of Environmental Engineering in the Department of Civil and Environmental Engineering at Carnegie Mellon University. He is also Faculty Director of the Steinbrenner Institute for Environmental Education and Research. He has published numerous articles in leading environmental engineering and science journals, book chapters, articles for the popular press, and has authored two books.
Athanasios K. Karamalidis, PhD
Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA
Athanasios K. Karamalidis is a Research Assistant Professor in the Department of Civil and Environmental Engineering at Carnegie Mellon University. He has conducted research on the dissolution and surface reactions of complex mineral assemblages in aqueous systems. His research also includes studies of geochemical phenomena for CO2 storage systems and shale gas development. He has published his work in peer-reviewed international journals in environmental engineering and science, in the proceedings of international conferences and has authored one book.
