This book addresses the use of environmental tracers and environmental isotopes for identifying groundwater sources and quantifying rates of groundwater recharge, discharge, flow, and mixing. Its goal is to present the application of the techniques in a form that can be readily understood and appreciated by groundwater professionals who do not have a background in the use of isotopes or other environmental tracers. The aim is to raise awareness of the potential of these tools, not to present all of the information that is required for their application in particular studies. Consequently, the details of sampling requirements, which sometimes involve specialized equipment, are not discussed. For most of the examples, the techniques were successfully applied. However, not all studies are so successful. Some of the limitations of the various tracers that contribute to failed studies are briefly discussed toward the end of this book and are widely discussed elsewhere.

In this book, emphasis is given to techniques that provide information on groundwater residence times, as these facilitate estimation of groundwater flow rates. The focus is on water quantity rather than quality, so the use of compound-specific isotopic techniques to determine sources of anthropogenic contamination is not considered. Also, the use of isotopes to determine geochemical reactions and pathways is not the focus of this book, although some of the examples demonstrate how residence time indicators have been used in conjunction with measurement of contaminant concentration to determine rates of plume movement or changes in contaminant concentrations over time. This book is focused on the saturated zone, thus does not discuss the use of environmental tracers to estimate soil evaporation or rates of plant water use.

While not the focus of this book, these other topics are of great interest. Isotopes and environmental tracers are being used more widely in groundwater science, and this book aims to facilitate the continuation of this increased use.