Case Studies in Groundwater Contaminant Fate and Transport

by

Barbara Bekins

• LAST REVIEWED: 03 January 2020
• LAST MODIFIED: 26 April 2018
• DOI: 10.1093/obo/9780199363445-0096

Introduction

A case study of groundwater contamination is a detailed study of a single site contaminated with a chemical or mixture that is known to be a problem at many sites. The goal of case studies is to provide insights into the physical, chemical, and biological processes controlling migration, natural attenuation, or remediation of common groundwater contaminants. Ideally, processes occurring at a case study site are representative of other sites so that knowledge gained from these intensive studies can be applied at thousands of sites where fewer data are available. Several characteristics of case studies contribute to their value. First, they may have tens to hundreds of monitoring wells, compared to fewer than ten wells at some contaminated sites. Second, some case studies continue for many years or even decades, providing insights into temporal progression of slow processes. Third, analytical methods prohibitively expensive for routine use or under development may be tested at case study sites. Finally, the ongoing characterization typical of case study sites builds a foundation of knowledge that facilitates sophisticated experimental design and testing of new methods. This article is divided into sections based on the contaminant type because the chemical and biological processes required for remediation vary for each contaminant. Most importantly, some contaminants can be biodegraded whereas metals and radionuclides cannot be destroyed but can be immobilized or rendered less toxic. The emphasis is on case studies of natural processes that control the fate and transport of contaminants in groundwater rather than on active remediation methods. The principles learned from these studies may form the basis for design of remedial strategies. The organic contaminants are divided into: petroleum hydrocarbons, fuel oxygenates, coal tar and wastes from manufactured gas plants, and chlorinated solvents. The inorganic contaminants covered are metals and radionuclides, arsenic, and nitrate. Case studies of mixed waste plumes from landfills are also described. Experimental sites where contaminants have been introduced into an aquifer as an emplaced source or a controlled release may not meet the above definition of case studies, but some are included because the overall goal is to impart lessons learned from detailed field studies. It is impossible to cover all case studies in this short format. Conversely, focusing on one or two does not convey the breadth of research results in entire range of case studies. Instead, the strategy is to describe the evolution of knowledge for each contaminant class while providing citations of relevant case studies. Much of the progress in understanding of the fate of contaminants in groundwater is based on laboratory studies; thus whenever possible, papers that included both field and laboratory results have been included among the citations. Two topics of growing importance have not been covered. These are the fate of pharmaceuticals in groundwater and discharge of contaminant plumes to surface water. These topics merit coverage in the future as knowledge grows and case studies increase in number.

Process Overviews and Reviews

The chemical properties of a contaminant and aquifer affect the reactions that occur in a groundwater contaminant plume. For example, some compounds biodegrade only under anaerobic conditions while others require aerobic conditions. A combination of organic and inorganic reactions may contribute to mobilizing or immobilizing contaminants such as arsenic or metals. These concepts are reviewed in NRC 2000 on natural attenuation. A chapter on the scientific basis for natural attenuation includes a basic explanation of reduction and oxidation (redox) reactions followed by a summary of the effect of redox conditions on microbial transformation of each major contaminant class. Inorganic reactions are also covered, including acid-base, redox, precipitation and dissolution, complexation, sorption, hydrolysis, and decay. More than ten case studies illustrate the processes affecting a range of contaminants in groundwater. A compilation of eighty case studies, NRC 2013 covers complex sites where contaminants are resistant to natural degradation and the subsurface is highly heterogeneous or fractured. The role of redox reactions on the fate of contaminants in groundwater and methods for determining redox conditions are described in Christensen, et al. 2000. A number of review articles cover specific classes of contaminants. Cozzarelli, et al. 2014 provides an overview of the composition, properties, and natural attenuation processes of petroleum fuels and oxygenates. The properties of methyl tertiary butyl ether (MTBE) that contributed to its widespread groundwater contamination and the history of its use are presented in Rosell, et al. 2006. A review of polycyclic aromatic hydrocarbon (PAH) remediation in soils, Kuppusamy, et al. 2017 notes the most important sources are manufactured gas plants followed by wood treatment sites, which are covered in a case study section of this article. A comprehensive book on natural attenuation of chlorinated solvents and fuels, Wiedemeier, et al. 2007 describes attenuation mechanisms and investigative strategies illustrated with case studies. Adriaens, et al. 2014 covers halogenated hydrocarbons in the environment including other compartments besides groundwater. A review of heavy metal remedial strategies for groundwater, Hashim, et al. 2011 covers speciation and chemistry, concentration limits, and provides citations of case studies. The global distribution of arsenic contamination is summarized in Ravenscroft, et al. 2009, along with hydrogeochemistry, hydrogeology, and mitigation strategies. Fowler, et al. 2013 compiles global sources of reactive nitrogen to show that over half of the total is anthropogenic from fertilizer and biological fixation by crops. Two reviews of natural attenuation processes in landfill leachate plumes cover conceptual understanding and research developments with illustrations from case studies (see Christensen, et al. 2001 and Bjerg, et al. 2014, cited under Landfills).

• Adriaens, P., C. Gruden, and M. L. McCormick. 2014. Biogeochemistry of halogenated hydrocarbons. In Treatise on geochemistry. 2d ed. Vol. 11. Edited by H. D. Holland and K. K. Turekian, 511–533. Oxford: Elsevier.

  Comprehensive review of sources of halogenated hydrocarbons and reactions in the environment including microbially mediated, surface mediated, and organic matter mediated. Both chlorinated aromatic and aliphatics are included. The scope covers the fates in the atmosphere, as well as soil, groundwater, and sediments. As a result, specific information about groundwater is limited.

• Christensen, T. H., P. L. Bjerg, S. A. Banwart, R. Jakobsen, G. Heron, and H. J. Albrechtsen. 2000. Characterization of redox conditions in groundwater contaminant plumes. Journal of Contaminant Hydrology 45.3–4: 165–241.

  DOI: 10.1016/s0169-7722(00)00109-1

  Provides a short tutorial on redox reactions and covers important reactions in groundwater relevant to fate of groundwater contaminants. It describes the difficulties in measuring redox conditions and reviews existing methods illustrated with applications.

• Cozzarelli, I. M., J. R. McKelvie, and A. L. Baehr. 2014. Volatile hydrocarbons and fuel oxygenates. In Treatise on geochemistry. 2d ed. Vol. 11. Edited by H. D. Holland and K. K. Turekian, 439–480. Oxford: Elsevier.

  Provides an overview of sources and processes affecting volatile hydrocarbons and fuel oxygenates in the environment. Reviews the petroleum industry with examples of contamination sources during production, transport, refining, and storage. Covers human exposure pathways and problems with assessing toxicity of mixtures. Describes abiotic and biotic transformations and natural attenuation in groundwater with examples from two case studies.

• Fowler, D., M. Coyle, U. Skiba, et al. 2013. The global nitrogen cycle in the twenty-first century. Philosophical Transactions of the Royal Society B-Biological Sciences 368.1621: 13.

  DOI: 10.1098/rstb.2013.0164

  This review quantifies the sources of reactive nitrogen in the environment. Anthropogenic sources including fertilizer and crops contribute over half of the global sources. The review also covers the amount of unintended N loss to leaching and runoff in agricultural settings globally.

• Hashim, M. A., S. Mukhopadhyay, J. N. Sahu, and B. Sengupta. 2011. Remediation technologies for heavy metal contaminated groundwater. Journal of Environmental Management 92.10: 2355–2388.

  DOI: 10.1016/j.jenvman.2011.06.009

  This highly cited review of remedial technologies for heavy metal contaminated groundwater has tables of speciation and chemistry with references for further reading. A total of thirty-five technologies are described organized into chemical, biological, and physico-chemical processes.

• Kuppusamy, S., P. Thavamani, K. Venkateswarlu, Y. B. Lee, R. Naidu, and M. Megharaj. 2017. Remediation approaches for polycyclic aromatic hydrocarbons (PAHs) contaminated soils: Technological constraints, emerging trends and future directions. Chemosphere 168: 944–968.

  DOI: 10.1016/j.chemosphere.2016.10.115

  This review begins with a ranking of the important sources of PAH contamination, followed by a section on mechanisms for PAH losses. Four established techniques and four emerging technologies for active remediation of PAH-contaminated soil are described and reviewed. The emphasis is on methods that have been proven to work at field sites.

• NRC. 2000. Natural attenuation for groundwater remediation. Washington, DC: National Academy Press.

  This book reviews the natural attenuation reactions for different classes of contaminants and provides a summary of the likelihood that remediation by natural attenuation will be successful. An excellent chapter on community concerns forms a framework for the issues addressed in the book. A chapter on demonstrating natural attenuation covers methods for mass balance calculations, demonstrating the occurrence of reactions, and principles for assessing uncertainty.

• NRC. 2013. Alternatives for managing the nation’s complex contaminated groundwater sites. Washington, DC: National Academy Press.

  Discusses how to handle sites with complex geology and sources. It includes eighty case studies and how they were handled.

• Ravenscroft, P., H. Brammer, and K. Richards. 2009. Arsenic pollution: A global synthesis. Wiley-Blackwell.

  DOI: 10.1002/9781444308785

  Provides a worldwide summary of arsenic pollution organized by continent. Chapters cover geochemistry, hydrogeology, agriculture, health effects, methods for removal from drinking water and water supply mitigation.

• Rosell, M., S. Lacorte, and D. Barcelo. 2006. Analysis, occurrence and fate of MTBE in the aquatic environment over the past decade. Trac-Trends in Analytical Chemistry 25.10: 1016–1029.

  DOI: 10.1016/j.trac.2006.06.011

  Provides an overview of the global use of MTBE in gasoline, analytical methods, and occurrence and behavior in the environment. MTBE is one of several oxygenates used in reformulated gasoline. A table comparing chemical and physical properties of fuel oxygenates shows how the properties of MTBE led to its high mobility and difficulty of removal from groundwater by either aeration or biodegradation.

• Wiedemeier, T. H., H. S. Rifai, C. J. Newell, and J. T. Wilson. 2007. Natural attenuation of fuels and chlorinated solvents in the subsurface. Hoboken, NJ: John Wiley.

  This is a comprehensive book on natural attenuation initially published in 1999 and published online in 2007. Covers principles of natural attenuation, abiotic reactions and intrinsic bioremediation of chlorinated solvents, intrinsic bioremediation of fuels, modeling natural attenuation, and design of long-term monitoring programs. Chapters on case studies of chlorinated solvents and fuels each cover four sites.