Groundwater contamination by numerous constituents from a variety of sources threatens current and prospective water supplies. Effective management under the pressures of increasing and shifting water demands requires a deep and quantitative understanding of contaminant hydrogeology. However, few textbooks are focused on the topic and fewer have been updated since the 1990s. The new textbook from The Groundwater Project, Modern Subsurface Contaminant Hydrology (Sale and Scalia 2025), is an important contribution that starts to fill this gap. The first chapter explains how the presentation of contaminant hydrogeology in this book differs from previous works. Simply put, this book is written from the standpoint that subsurface porous media are heterogeneous and the inherent heterogeneity of geologic materials drives much of what we observe in contaminant hydrogeology. This is a departure from the standard “classroom aquifers,” as the authors call them, which represent the subsurface as homogeneous and isotropic. Geologic heterogeneity often results in juxtaposition of lower and higher permeability materials. The authors assert that diffusion of contaminants into and out of low permeability zones is the primary solute spreading process in groundwater and that storage and release of contaminants from these zones exerts a strong control over plume longevity and the success of many remediation strategies. Consequently, the authors emphasize the importance of diffusion as a transport process in most groundwater systems rather than a process only relevant to settings with extremely low permeability. The second chapter (Foundations) introduces readers to the basic processes and properties controlling contaminant migration and the mathematical nomenclature used throughout the book. The authors generally follow the nomenclature of chemical and petroleum engineering. This may be difficult for some readers who are already familiar with these equations from other disciplines. However, terms are well defined and used consistently throughout the text, so once the initial translation hurdle is overcome, the text is easy to follow. Chapter 3 (Transport) presents the basics of advection but also provides coverage of more advanced topics. There is a comprehensive section on multiphase fluid flow describing how fluid saturations and capillary pressures control fluid migration. A subsequent section focuses on diffusion as an important transport process in groundwater systems. This section begins by describing the concept of diffusion at a molecular scale, then explains how diffusion proceeds in the pore space and finishes by providing examples of how diffusion into and out of low permeability media can support long-term tailing of concentrations in contaminant plumes. Chapter 4 (Reactions) begins with observations from field sites, followed by an overview of basic chemical principles, including thermodynamics. The bulk of the chapter is focused on contaminant partitioning between phases, primarily for non-aqueous phase liquids (NAPLs), air, water, and aquifer solids systems. The transformation section is brief, providing an overview and examples of zeroth, first, and second order reactions. The fifth chapter focuses on mathematical modeling. One of the central tenets of the book is that mathematical models are critical tools for integrating observations and testing hypotheses in contaminant hydrogeology. The chapter begins by discussing the reasons for modeling and presenting the foundational governing equations. The remainder of the chapter describes several approaches to numerical modeling where diffusive mass transfer between low and high permeability zones is represented. Many example outputs are included to demonstrate the impact of diffusion on contaminant transport and remediation. The book includes several features useful to a variety of readers. For example, “calculation vignettes” are incorporated into the text to provide readers with quantitative examples of concepts. The book also includes 39 additional short-answer questions with corresponding answers so readers can test their own understanding of the content. Lastly, there are many field and laboratory photos of contaminant transport processes, as well as example data sets and simulation results from actual contaminated sites. Although the book's coverage is comprehensive, some topics are not covered in detail. For example, the content focuses on contaminant issues stemming from NAPLs with far less coverage of other contaminant types such as nutrients, metals, and pathogens. Abiotic and biotic transformation of organic contaminants is mentioned as important reactions and readers are referred to other works for a full accounting of these processes. Lastly, the topic of mechanical dispersion is not covered except to assert that it is generally a weak process in porous media. The authors refer readers to other works with alternative views of mechanical dispersion. The combination of foundational content with real world examples makes this book suited for an upper-level undergraduate or graduate course in contaminant hydrogeology focused on quantitative understanding of transport and fate. Instructors using this book should be aware of some minor errors, such as variations in nomenclature between the figures and the text and some missing or incorrect labels on figures. The book would also be valuable as a reference for practicing hydrogeologists; the transport/attenuation scenarios presented are useful examples for conceptual models. Given the increasing importance of groundwater, the world needs more hydrogeologists with strong, quantitative foundations in contaminant hydrogeology. Modern Subsurface Contaminant Hydrology provides an excellent and much-needed resource for students, instructors, and current practitioners alike. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
Jessica Meyer (Tue,) studied this question.