Quantifying Matrix Diffusion and Redox Effects on Hexavalent Chromium Plume Conditions in a Fractured Mudstone

Parker, Beth L.

Quantifying Matrix Diffusion and Redox Effects on Hexavalent Chromium Plume Conditions in a Fractured Mudstone

Tuesday, October 3, 2017: 8:30 a.m.

Beth L. Parker, Ph.D. , College of Physical and Engineering Science, G360, University of Guelph, Guelph, ON, Canada

Steven Chapman, P.E. , G360 Centre for Applied Groundwater Research, University of Guelph, Guelph, ON, Canada

Tom A. Al, Ph.D. , Earth Sciences, University of Ottawa, Ottawa, ON, Canada

Jiujiang Zhao , Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, ON, Canada

Rick Wilkin, Ph.D. , Office of Research and Development, EPA, Ada, OK

Diana M. Cutt, PG , Office of Research and Development, USEPA Region 2, New York, NY

Katherine Ryan Mishkin , Superfund Division, USEPA Region 2, New York, NY

It is well known that diffusion driven mass transfer between fractures and the rock matrix controls plume transport and fate in fractured sedimentary bedrock aquifers. Effects can be positive since mass transfer from groundwater flowing in fractures to the rock matrix reduces rates of plume migration and mass flux to receptors, and negative since mass stored in the matrix acts as an impediment to groundwater restoration. While much attention has been focused on chlorinated solvents, there has been little focus on matrix diffusion effects at metals contaminated sites. This study involves a Superfund site in New Jersey, where a hexavalent chromium plume emanates from a former electroplating facility and migrates within a fractured mudstone aquifer discharging to a river. Hexavalent chromium is a contaminant of concern at many sites and can be highly mobile in aquifer systems; however redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to immobile Cr(III) precipitates. A discrete fracture network (DFN) framework was applied for characterization, including collection of detailed profile of Cr mass distribution in the low permeability matrix by subsampling continuous cores with development of new laboratory extraction techniques to quantify both mobile Cr(VI) in porewater and Cr(III) precipitates. Supporting field data included geophysical and hydrophysical methods for fracture network and flow system characterization and installation of a multilevel system for depth-discrete hydraulic head and groundwater sampling for Cr(VI), hydrochemistry and Cr-isotopes. Results show matrix diffusion and reaction processes are influencing the plume including Cr(VI) reduction and immobilization in the rock matrix as Cr(III), which can significantly enhance plume attenuation in combination with matrix diffusion and limit potential for back diffusion if the reduction is irreversible. This presentation will provide an update on study results and implications.

Beth L. Parker, Ph.D., College of Physical and Engineering Science, G360, University of Guelph, Guelph, ON, Canada

Beth Parker, Ph.D., University of Guelph Professor in the College of Physical and Engineering Sciences and Director of the G360 Centre for Applied Groundwater Research, has more than 30 years of experience investigating subsurface contamination at numerous sites around the world, using high resolution data sets for site conceptual model development and testing. Her current research activities emphasize developing improved field and laboratory methods for characterizations and monitoring of industrial contaminants in sedimentary rocks, clayey deposits, and sandy aquifers, and focus on the effects of diffusion in low permeability zones, plume attenuation, and hydrogeologic controls on remediation.

Steven Chapman, P.E., G360 Centre for Applied Groundwater Research, University of Guelph, Guelph, ON, Canada

Steven Chapman is a Senior Research Engineer/Hydrogeologist in the G360 Centre for Applied Groundwater Research in the School of Engineering at the University of Guelph. He is a Professional Engineer (Civil) with an M.Sc. from the University of Waterloo (Earth Sciences) and has more than 20 years of hydrogeologic experience. His research focuses on contaminant behavior in unconsolidated porous media and sedimentary rock, involving high resolution site characterization at industrial and research sites and numerical modeling, with a focus on the role of diffusion including impacts on remediation performance.

Tom A. Al, Ph.D., Earth Sciences, University of Ottawa, Ottawa, ON, Canada

Tom Al is a Full Professor in the Department of Earth Sciences at the University of Ottawa. His research interests include mineral-water reaction processes that affect transport of contaminants in groundwater and surface water, geochemical and hydrologic processes controlling the release and transport of metals from sulfide-bearing mine waste, and geochemical reaction processes associated with in-situ oxidation of organic contaminants in groundwater.

Jiujiang Zhao, Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, ON, Canada

Jiujiang Zhao is a Postdoctoral Fellow.

Rick Wilkin, Ph.D., Office of Research and Development, EPA, Ada, OK

Rick Wilkin is an environmental geochemist.

Diana M. Cutt, PG, Office of Research and Development, USEPA Region 2, New York, NY

Diana Cutt, PG, is Superfund and Technology Liaison for the EPA Region 2 Office of Research and Development.

Katherine Ryan Mishkin, Superfund Division, USEPA Region 2, New York, NY

Katherine Ryan Mishkin serves as a Geologist in the Technical Support Section of Superfund in EPA Region 2.