If 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. in your model are defined as being independent of the concentration of the 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). (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.
In many systems, however, species partition between 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. (e.g., water and sediment) according to a non-linear isotherm, in which the degree of partitioning varies with concentration. Non-linear isotherms can be readily represented in GoldSim by defining the partition coefficients as functions of the concentrations.