14.1 Introduction

We’ve looked at groundwater and we’ve looked at surface water…now let’s look at what is between the two. The layer between the ground surface and the water table—commonly referred to as the unsaturated zone—contains a combination of water and air. This part of the subsurface is important for several reasons: The soils and moisture in this zone support plants, chemical and organic processes filter contaminants and affect the chemistry of groundwater, and the unsaturated zone is an avenue of recharge to unconfined aquifers. The same basic laws of physics that govern the flow of fluids in saturated units are at work in the unsaturated zone, however, the processes involved are much more complicated in the unsaturated zone than they are in saturated rock and sediment. In this section, we discuss some of the processes at work in the unsaturated zone.