Water Wheel Nov/Dec 2025: Groundwater

Abstract

In groundwater research (hydrogeology), the term ‘groundwater age’ is frequently used as a proxy for the time elapsed since a water parcel infiltrated the subsurface and entered the groundwater system. While the term may serve as a useful conceptual approximation, its application in fractured and heterogeneous aquifer systems requires careful consideration. Unlike a sealed bottle of wine, which follows a relatively predictable chemical evolution under controlled conditions, groundwater in fractured aquifers does not ‘age’ uniformly. Some water flows quickly through open fractures, while other portions linger in tiny rock pores for decades or centuries. As a result, a water sample from a borehole is rarely of one single age, but rather a blend of waters of many different ages. It flows through fractures and rock pores at variable rates, mixes continuously, and interacts chemically with the surrounding environment, making its residence times highly variable and far less predictable. A useful way to think about this is like a shopping mall.

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