Contaminant Transport from Land Surface to Groundwater - Contaminant Geochemistry - page 242

Part IV
Contaminant Transport from Land
Surface to Groundwater
In the previous sections of this topic, we focused on the nature of contaminants and
the geochemical reactions that can occur in the subsurface environment. Chemical
compounds introduced into infiltrating water or in contact with soil or rock surfaces
are subject to chemically and biologically induced transformations. Other
compounds are retained by the soil constituents as sorbed or bound residues.
Thus, in terms of geochemical interactions and reactions among dissolved chemical
species, interphase transfer occurs in the form of dissolution, precipitation,
volatilization, and various forms of physicochemical retention on the solid surfaces.
These phenomena do not occur in a ''static'' domain: chemical compounds
migrate and are redistributed along the soil profile, down to the water table region,
and within the fully saturated aquifer zone, by flowing water. The extent of this
redistribution and the kinetics of the geochemical interactions are controlled by the
very nature of fluid flow in porous media, the water chemistry, and of course the
properties of the soil and contaminant(s).
To describe and quantify these complex dynamics, models are used. Modeling of
contaminant transport involves formulation of a conceptual framework and
corresponding quantitative relationships that lead to determination of contaminant
distributions over space and time. Models can also be used to investigate the relative
influence of different physical and (geo)chemical mechanisms on contaminant
transport and to assist in designing management and remediation strategies.
The next chapters consider the dynamics of flow and transport of water and
chemical compounds, as they migrate from land surface to the groundwater
regime. In Chap. 9 , we focus on water flow in the partially saturated zone and
through the capillary fringe into the saturated regime below the water table.
Chapter 10 then treats (non-chemically reactive) transport mechanisms that govern
migration of chemical species, while Chap. 11 integrates the effects of water flow,
chemical transport, and geochemical interactions through the subsurface envi-
ronment. Finally, Chap. 12 considers selected research findings, providing specific
examples of the transport behaviors discussed here.