Basic Solid Properties

A Solid has four basic properties: a Dry Density, a Porosity, a Tortuosity, and a set of Partition Coefficients.

Dry (bulk) Density: The Dry Density is defined as the mass of Solid divided by the total volume of the Solid (volume of solid plus volume of pores). It is used by Pipe and Aquifer pathways to compute retardation properties when the Solid is assigned to one of these pathway types. The Dry Density is also used if you specify fractional Available Porosities for the Solid.

Note: The Dry Density is not the specific gravity of the solid. It is defined as (V_s ρ_s)/(V_s + V_v), where V_s is the volume of the solids, V_v is the volume of voids, and ρ_s is the specific gravity of the solid.

Porosity: The Porosity is the ratio of pore volume to the total volume of the Solid. That is, it is defined as V_v/(V_s + V_v), where V_s is the volume of the solids, and V_v is the volume of voids. This input is used when you define a diffusive flux link in which the Solid is present in one of the linked pathways and is specified as the porous medium through which the transport takes place. In this case, the Porosity and Tortuosity are multiplied by the diffusivity of the species in the fluid to determine an effective diffusivity for transport. The Porosity is also used to compute the transport properties when the Solid is assigned to an Aquifer or Pipe pathway.

Tortuosity: The Tortuosity quantifies the degree to which diffusion is slowed down due to the tortuous path that a diffusing species must travel as it moves through the pore space in the Solid. The tortuosity should be specified as a value which is less than or equal to one. This input is used when you define a diffusive flux link in which the Solid is present in one of the linked pathways and is specified as the porous medium through which the transport takes place. In this case, the Porosity and Tortuosity are multiplied by the diffusivity of the species in the fluid to determine an effective diffusivity for transport. Porosity is also used in matrix diffusion calculations for Pipe pathways.

Note: The Tortuosity is defined in different ways in different fields. Within GoldSim, it is defined such that the smaller the Tortuosity, the more tortuous the path. In some fields, the Tortuosity is defined as the inverse of how it is defined in GoldSim, such that more tortuous paths have a higher Tortuosity.

Note that the tortuosity as used by GoldSim is based on a porous medium that is fully saturated with a single fluid, typically water or air. For partially saturated media, the effective diffusivity is further reduced (by a Diffusive Reduction Formula, which is a property of the fluid through which the species is diffusing).

Partition Coefficients: The partition coefficient is defined as the ratio, at thermodynamic equilibrium, of the concentration in the solid to that in the Reference Fluid. The partition coefficient for a solid has dimensions of volume/mass.

This input requires that you enter 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). Partition Coefficients are actually an elemental property, as opposed to a species property. As such, they should be specified for every element (rather than species). GoldSim, however, allows you to enter them either by species or element. Note that if you have defined species that represent isotopes of the same chemical element, the Partition Coefficients must be identical for all isotopic species of the element (and GoldSim will enforce this). 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.

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).

You can enter constants, expressions, or links into the fields for each element. The default value is 0 m3/kg (elements do not partition onto the Solid).

If you wish to enter a link to define the entire vector, rather than defining the vector locally, you must first press the Clear 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.

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 Partition Coefficient (if data is entered as species, the Partition Coefficient for the first species in the list will be applied to all isotopes).

Note: You can paste data from a spreadsheet, a Word table or a comma-delimited text file into any of the vector editing dialogs for a Solid by copying the data to the clipboard, single-clicking in the cell representing the top of the target range, and pressing Ctrl+V.