When species The chemical (or non-chemical, such as bacterial or viral) constituents that are stored and transported through an environmental system in a contaminant transport model. In GoldSim, the Species element defines all of the contaminant species being simulated (and their properties). mass enters a Cell, it is instantaneously partitioned among the media Materials (such as water, sand, clay, air) that constitute (are contained within) transport pathways. GoldSim provides two types of elements for defining media: Fluids and Solids. present in the Cell. The partitioning is controlled by the partition coefficients The ratio of the species’ concentration in a medium to its concentration in the Reference Fluid at equilibrium. Partition coefficients are inputs to Solid and Fluid elements. defined for each species in each medium, and the quantity of each medium present. In particular, in the absence of solubility limits, the concentration of species i in Medium x is computed by GoldSim as follows:
where:
cxi = concentration of species i in medium x in the cell
[(M/L3) for Fluids or (M/M) for Solids];
mi = mass of species i in the cell [M];
Kxi = partition coefficient between medium x and Reference Fluid A special type of Fluid element that provides a basis for defining partition coefficients between media for the various species in the model (i.e., the ratio of the species’ concentration in the medium to its concentration in the Reference Fluid at equilibrium). for species i
[(L3 /L3) for Fluids or (L3/M) for
Solids];
Kgi = partition coefficient between medium g and Reference
Fluid for species i [(L3
/L3) for Fluids or (L3/M) for
Solids];
VMg = quantity (volume or mass) of medium g in the cell
[L3 for Fluids or M for Solids]; and
NM = the number of media in
cell.
Note that, by definition, for all species the partition coefficient between the Reference Fluid and itself is 1 (i.e., in the above equation, if x is the Reference Fluid, Kxi = 1).
Note: If the partition coefficients are defined as being independent of the concentration of the species (at a given temperature), the concentrations then vary linearly with mass in the cell (assuming no solubility constraints). This relationship is referred to as a linear isotherm. Non-linear isotherms, in which the degree of partitioning varies with concentration, can be readily represented in GoldSim by defining the partition coefficients as functions of the concentrations.