Foreword
The elapsed time groundwater takes to travel from its recharge area to any point in a groundwater flow domain—such as to a monitoring well—is an important number that results from a combination of physical properties of the flow system. The elapsed time depends on the rate of recharge to the flow path as well as the distribution of hydraulic conductivity and porosity of the geologic media along the flow path between the recharge area and the well.
To determine the values of these parameters would involve much effort and expense and is rarely accomplished. An alternative method involves collecting a water sample from the well and subjecting it to measurements that allow an estimate of the travel time to be calculated. This estimate is known as the groundwater age for the well or spring; when these age dating methods are applied in a study area, age determinations are made on several or even many wells.
This book concerns the age dating of groundwater less than 60 years old, adding to the body of knowledge presented in the previously published GW Project book Introduction to Isotopes and Environmental Tracers as Indicators of Groundwater Flow (Cook, 2020), which provides an overview of all of the environmental tracers used to estimate groundwater age, including those applied to water much older than 60 years. This book is intended for those who seek to apply age dating methods or who want to understand the nature of and uncertainties in age values reported in the literature, particularly with respect to young groundwater.
Laboratories that conduct age dating measurements on samples as indicated in this book operate in several countries; thus, anyone who seeks these analyses can obtain them on a fee per sample basis. This important advancement means that age dating of groundwater less than 60 years old has moved beyond the experimental stage to being an important tool that can be applied in many types of investigations.
The authors of this book, Dr. Kip Solomon, a professor at the University of Utah, and Dr. Troy Gilmore, an associate professor at the University of Nebraska, are experienced in many different hydrogeologic settings. Over the course of their careers, they have produced a substantial portion of the existing literature concerned with dating methods used on young groundwater.
John Cherry, The Groundwater Project Leader
Guelph, Ontario, Canada, November 2023