17.1 Introduction

We’ve discussed various aspects of groundwater flow, ranging from the properties of porous media to the response of aquifers to a pumping well to the study of regional flow systems to the chemistry of groundwater systems. Most of our discussions dealt with idealized conceptual systems, like a perfectly confined aquifer, or a homogeneous layer of sand, or a set of evenly spaced fractures with a constant aperture. But the natural world is not ideal like those conceptualizations. Groundwater occurs in a variety of different geologic settings, from unconsolidated alluvium to karstified limestone to fractured granite, and each geologic setting has specific geologic and hydrogeologic characteristics. To study and understand hydrogeologic systems, one needs to first understand the geology. In this section, we will look at the occurrence of groundwater in a variety of geologic systems and examine the relationship between geology and the water that is flowing through it.