Groundwater Geochemistry and Isotopes

A book review by Laura Newsome
University of Exeter
l.newsome@exeter.ac.uk
ECG Bulletin January 2020

An introduction to understanding groundwater chemistry, groundwater processes, and the behaviour of stable isotopes and radioisotopes in groundwater.

This is an excellent reference book for anyone who wishes to discover more regarding the processes that influence groundwater chemistry and the behaviour of isotopes. Having recently been in a meeting where the behaviour of stable isotopes in groundwater was discussed, I thought this was an excellent time to review this book. Given the subject of the meeting, I decided it was best to start with Chapter 7: Geochemical Evolution. This chapter starts by describing the reactive components of aquifers (clay minerals, humics, iron and manganese oxyhydroxides, colloids, and zeolites) and the processes that occur during the evolution of natural groundwater geochemistry. These include processes such as cation exchange, adsorption, redox reactions, and the influence of salinity. The chapter concludes with a description of how to present geochemical evolution in a graphical format. Each of these topics was explained in a clear, easy to follow way, with helpful derivations of equations and Pourbaix diagrams. I liked how microbial activity was clearly linked to the development of reducing conditions, as well as the descriptions of how microbial activity influenced the fraction of stable isotopes such as ³⁴S, ¹⁸O, ¹³C, and ²H in groundwater.

Next, I looked at Chapter 9: Contaminant Geochemistry and Isotopes. This chapter will be of particular interest to those working in the contaminated land industry. It starts by explaining the biogeochemistry of nitrogen compounds (including ammonia, urea, and nitrate) in groundwater, including sources from agriculture and wastewater. Next, it details the biodegradation of organic compounds such as hydrocarbons and organohalogens, contamination from which is the biggest issue impacting the UK groundwater environment. Subsequently, it describes the processes that influence contaminant behaviour in landfills and acid mine drainage. This is followed by sections on individual base metals (Cr, Mn, Co, Ni, Cu, and Zn). The issue of groundwater salinisation and isotope behaviour is covered in some detail, and the problems of groundwater contamination by arsenic and nuclear waste are afforded their own sections.

Returning to start of the book, it was useful to find that the introductory chapter contained clear explanations of aquifer geological components, and charge balance and of stable isotope fractionation calculations. Chapter 2: Thermodynamics of Aqueous Systems, Chapter 3: Geochemical Reactions and Chapter 4: Isotope Reactions covered the necessary basics required to understand groundwater geochemistry and isotope behaviour. Other chapters cover carbon dioxide and weathering, groundwater dating, and sampling and analysis.

In summary, this book is an excellent resource for those who have limited experience working with groundwater or who are studying this topic. I would also recommend it as a useful reference for more experienced practitioners.

Reference
Clark, I., Groundwater Geochemistry and Isotopes, CRC Press, Boca Raton, Florida, 2015,      ISBN:9781466591738.