Advanced Solid Properties

Solids have three additional properties that are typically only required for advanced contaminant transport applications. Most users can ignore these inputs. These are accessed via the Advanced Properties… button:

Available Porosities: The Available Porosity represents the fraction of the pore volume within the Solid that is accessible to each species. The Available Porosity is dimensionless. It must be greater than or equal to 0 and less than or equal to 1.

Available Porosities must be specified for every species. Note, however, that this is actually an elemental property, as opposed to a species property. That is, if you have defined species that represent isotopes of the same chemical element, the Available Porosities must be identical for all isotopic species of the element. (If you are not simulating isotopes, you need not be concerned with this, as there is then a one-to-one correspondence between each species and each element).

This input requires that you enter a dimensionless vector by element (a vector with an item for each chemical element) or a vector by species (a vector with an item for each species). By default, the vector is defined locally as a vector by (chemical) element, which means that you can edit it directly from this dialog (by pressing the Edit… button to the right of the input field).

Note: The Elements array label set is always in alphabetical order.

You can enter constants, expressions, or links into the fields for each species. The default value is 1 (no unavailable porosity).

If you wish to enter a link to define the entire vector, rather than defining the vector locally, you must first press the Clr button. This will clear the local vector, and make the edit field available to you for entering a link. When entering a link, you can link to either a vector by element (a vector with an item for each chemical element) or a vector by species (a vector with an item for each species).

Note: If you link to a vector by species, and then subsequently decide to specify the vector locally (by pressing the Edit… button), the dialog for entering the data locally will be presented in terms of species. To change this back to a local vector by elements, you must first link to a dimensionless vector of elements, and then press the Edit… button again.

An available porosity less than 1 indicates that some of the pore volume is inaccessible for that species. Implementing an available porosity which is less than 1 may be appropriate when simulating Cell Pathways involving media such as clay, where processes such as anion exclusion may be active. For most applications, however, the available porosities should be left at the default value of 1 (i.e., no inaccessible porosity). This input requires that you enter a vector by species (a vector with an item for each species).

The Available Porosity of an element defines the fraction of the pore volume within the solid medium which is accessible to that element. A value less than 1 decreases the volume of water available to the species. Decreasing the volume of water available affects concentrations (since all of the mass of the porous medium is still assumed to be available, but only a fraction of the water is).

The impact of specifying a fractional available porosity for a solid on mass transfer rates is complex. For example, for diffusive mass flux links (and matrix diffusion zones) in which the Solid is specified as the porous medium, the effective diffusivity for the element of interest is multiplied (reduced) by the Accessible Porosity. For advective mass flux links in which the Solid is specified as the porous medium, the porosity is multiplied (reduced) by the Accessible Porosity.

Note: If you are simulating isotopes of the same element, regardless of how the data is entered, GoldSim will automatically ensure that isotopic species use the same values for the Available Porosity (if data is entered as species, the Available Porosity for the first species in the list will be applied to all isotopes).

Relative Particulate Diffusivity: You can specify that a Solid is present in a Cell pathway as a suspended particulate. In such a case, the particulate can diffuse through a diffusive mass flux link, carrying sorbed species. This input represents the relative diffusivity of the particulate form of the Solid. The same value is applied to all Fluids in which the Solid is suspended. Similar to the relative diffusivity for a species, the relative diffusivity for a particulate Solid is unitless, and is multiplied by the Reference Diffusivity of the corresponding Fluid to determine the actual diffusivity of the particulate form of the Solid in the Fluid.

Advective Velocity Multiplier: You can specify that a Solid is present in an Aquifer, Pipe, Cell or Network pathway as a suspended particulate. In such a case, the particulate can advect (and, in the case of Aquifers, Pipes and Network pathways, disperse) through an advective mass flux link from the pathway, carrying sorbed species. This input allows you to specify a factor that controls the velocity of the advected particulate Solid relative to the advecting Fluid. The default value is 1 (it moves at the same velocity as the Fluid). But you can choose to have the suspended Solid move faster or slower than the Fluid.