Dissolving and Precipitating Contaminants

Dissolution and precipitation can occur as contaminants travel from the land surface to groundwater aquifers. These processes can affect water chemistry, and they can significantly modify the physical and chemical properties of porous media (Lasaga 1984 Palmer 1996 Dijk and Berkowitz 1998, 2000 Darmody et al. 2000). Under some conditions, large quantities of mass can be transferred between the liquid and solid mineral phases. 

A number of experimental and theoretical studies analyzed the influence of dissolution processes on the physical and chemical properties of soluble porous matrices (Fogler and Rege 1986 Daccord and Lenormand 1987 Hoefner and Fogler 1988 Daccord 1987 Daccord et al. 1993). Similarly, several theoretical 

Loss or gain of dissolved chemical species from soil water by precipitation or dissolution, respectively, nsually is accounted for by adding a simple sink-source term in the advection-dispersion equation  

One approach to quantitatively relate changes in porosity to changes in specific surface area is to assume that the porous medium is composed of spherical grains. The resulting specific surface area per unit volume of rock, J, is related to the porosity, j), by the relationship (Lichtner 1988) 

Therefore, in the first model, the specific surface area increases with decreasing porosity, while in the second, the opposite relationship is specified. While some attempts have been made to experimentally verify these models in individual rock types (Kieffer et al. 1999 Jove Colon et al. 2004), the data concerning a wide range of rocks and precipitation-dissolution reactions remain limited. 

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