Geoscience Reference
In-Depth Information
Part I
Geochemistry Revisited: Selected Aspects
We conceived this topic on contaminant geochemistry not only for researchers in
hydrology, soil science, and geochemistry but also for advanced undergraduate
and graduate students in environmental sciences and various specialists working
on environmental pollution problems. As a consequence, we consider it useful and
necessary to include an introductory material that presents a short characterization
of porous media together with selected geochemical processes. Part I characterizes
subsurface components and the geochemical pathways and processes related to
potential contamination. Keeping in mind that contaminant geochemistry covers a
diverse range of natural and human-induced processes, we have selected only
those that are most relevant to our field of interest.
The first chapter presents the porous medium solid, liquid, and gaseous phases
in an environment controlled generally by fluctuations of rainy and dry periods,
reflected by a variety of saturated and partially saturated conditions. A description
of mineral and organic components in porous media is followed by a discussion of
the electrically charged surface properties that affect the near-solid phase water.
The composition of the subsurface water solution as affected by the surrounding
solid phase, by the natural biological environment, and possibly by human factors
also is discussed. The gaseous composition of porous media, which affects the
chemistry of the liquid phase, is another part of the subsurface environment.
Consideration of the aquifer environment, characterized by a saturated regime,
includes a brief discussion of groundwater geology and composition.
Selected geochemical processes that relate to the behavior of contaminants in
the subsurface are described in the second chapter. We focus on thermodynamic
considerations and equilibrium processes in the subsurface, accounting for
interactions among solid, liquid, and gaseous phases. Kinetic considerations in
defining the solubility of organics and minerals, as well as knowledge of chemical
potentials, ion activities, and reaction rate laws, are also included. The weathering
of subsurface solid phases, which occurs as a result of interactions with the liquid
phase, is a natural geological process that may be accelerated by anthropogenic
influences. Dissolution-precipitation and redox mechanisms are other important
