Page 24 - Hydrogeology Principles and Practice

HYDC01 12/5/05 5:44 PM Page 7

Introduction 7

The development of the chemical aspects of hy- attenuation processes as part of a managed approach
drogeology stemmed from the need to provide good to restoring contaminated land and groundwater.
quality water for drinking and agricultural purposes. Hence, hydrogeology has now developed into a
The objective description of the hydrochemical prop- truly interdisciplinary subject, and students who aim
erties of groundwater was assisted by Piper (1944) to become hydrogeologists require a firm foundation
and Stiff (1951) who presented graphical procedures in Earth sciences, physics, chemistry, biology, math-
for the interpretation of water analyses. Later, notable ematics, statistics and computer science, together
contributions were made by Chebotarev (1955), who with an adequate understanding of environmental
described the natural chemical evolution of ground- economics and law, and government policy.
water in the direction of groundwater flow, and
Hem (1959), who provided extensive guidance on the
study and interpretation of the chemical character- 1.5 The water cycle
istics of natural waters. Later texts by Garrels and
Christ (1965) and Stumm and Morgan (1981) pro- A useful start in promoting a holistic approach to link-
vided thorough, theoretical treatments of aquatic ing ground and surface waters is to adopt the hydro-
chemistry. logical cycle as a basic framework. The hydrological
By the end of the twentieth century, the previous cycle, as depicted in Fig. 1.5, can be thought of as the
separation of hydrogeology into physical and chem- continuous circulation of water near the surface of
ical fields of study had merged with the need to the Earth from the ocean to the atmosphere and then
understand the fate of contaminants in the subsurface via precipitation, surface runoff and groundwater
environment. Contaminants are advected and dis- flow back to the ocean. Warming of the ocean by
persed by groundwater movement and can simultan- solar radiation causes water to be evaporated into the
eously undergo chemical processes that act to reduce atmosphere and transported by winds to the land
pollutant concentrations. More recently, the intro- masses where the vapour condenses and falls as pre-
duction of immiscible pollutants, such as petroleum cipitation. The precipitation is either returned directly
products and organic solvents into aquifers, has led to to the ocean, intercepted by vegetated surfaces and
intensive research and technical advances in the the- returned to the atmosphere by evapotranspiration,
oretical description, modelling and field investigation collected to form surface runoff, or infiltrated into the
of multiphase systems. At the same time, environ- soil and underlying rocks to form groundwater. The
mental legislation has proliferated, and has acted as a surface runoff and groundwater flow contribute to
driver in contaminant hydrogeology. Today, research surface streams and rivers that flow to the ocean, with
efforts are directed towards understanding natural pools and lakes providing temporary surface storage.

Fig. 1.5 The hydrological cycle. The
global water cycle has three major
pathways: precipitation, evaporation and
water vapour transport. Vapour transport
from sea to land is returned as runoff
(surface water and groundwater flow).
Numbers in () represent inventories (in
3
6
10 km ) for each reservoir. Fluxes in [ ] are
3 −1
6
in 10 km a . After Berner and Berner
(1987).