Difference between revisions of "Physical processes and governing equations"
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The sorption behavior for chlorinated solvents on limestone was examined in Salzer (2013). | The sorption behavior for chlorinated solvents on limestone was examined in Salzer (2013). | ||
For chlorinated solvents like PCE, sorption to limestone can be strong (kd values of 0.5-1 L/kg were observed). | For chlorinated solvents like PCE, sorption to limestone can be strong (kd values of 0.5-1 L/kg were observed). | ||
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| + | === Determined hydraulic proporties for the Akacievej field site === | ||
| + | The following table gives an overview of values that were determined for the Akacievej site: | ||
| + | '''Include table with typical values for Akacievej''' | ||
Return to [[Content]] | Return to [[Content]] | ||
[[Category:Introduction]] | [[Category:Introduction]] | ||
Revision as of 14:43, 11 January 2017
Contents
Physical processes
Transport of substances in porous media can be subdivided in advective transport (due to the groundwater flow) and diffusive/dispersive transport. The storage of substances is strongly influenced by sorption of the substance to the porous medium. This is often quantified as retardation, using a retardation factor.
Fractured limestone has usually a strong contrasting flow conditions between fractures and matrix. The fractures can have very high flow velocities mainly depending on their aperture (width), whereas the limestone matrix has usually a very low hydraulic conductivity and thus low flow velocities. However, for the fate of contaminants in fractured limestone aquifer, the matrix is important, since it usually has a high porosity and can store substantial amounts of contaminants, once they have diffused into the matrix.
Governing equations
Flow
Groundwater flow in porous media is usually described by Darcy's law, giving a relation between hydraulic head gradient and groundwater flow. The fracture conductivity is usually determined via the fracture aperture using the cubic law.
Flow equation.
Contaminant transport
To describe the transport of a substance in a porous medium, the advection-dispersion equation is usually employed. The first term describes storage (here including retardation due to linear sorption), the second and third terms describe advective and dispersive transport of a substance. Degradation can be included as additional term.
Variables are:
| n | porosity |
| rho_b | bulk density |
| k_d | sorption coefficient |
| c | concentration |
| v | flow velocity |
| D_m | dispersion coefficient |
Properties of limestone
Limestone can be heavily fractured and include almost impermeable chert layers and nodules. The limestone found at the Akacievej site (Copenhagen kalk and bryozoan limestone) has a strongly varying hardness.
The sorption behavior for chlorinated solvents on limestone was examined in Salzer (2013). For chlorinated solvents like PCE, sorption to limestone can be strong (kd values of 0.5-1 L/kg were observed).
Determined hydraulic proporties for the Akacievej field site
The following table gives an overview of values that were determined for the Akacievej site: Include table with typical values for Akacievej
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