Cell Pathway Example 1: Equilibrium Partitioning, Decay, and Ingrowth

Cell Pathway elements can be used simulate partitioning between the liquid and solid media as well as nuclear decay of species. If you are using the Radionuclide Transport (RT) module, nuclear decay can be extended to simulate the ingrowth of daughter products as the result of the decay. This is the RT version of the "Cell1_PartitionDecay.gsm" example model.

In this example, a closed pond system composed of water and sediment is simulated, with an initial Species A amount of 10 g and no initial amount of species B. The system is closed because there is no in flow or out flow and water volume is fixed as is sediment mass. The process of nuclear decay acts to reduce the mass of species A (i.e. only species A can decay) over time. The complimentary ingrowth process converts the mass of species A which decays to species B which is defined as the daughter product for species A.

The process of equilibrium partitioning acts to always keep the mass of species A partitioned between the media according to the specified equilibrium partitioning rate (e.g. specified in m3/kg). Species B does not partition because equilibrium partitioning for species B is not specified. Additionally, ingrowth of species B is only is only simulated in the fluid medium.

10 g of species A and 0 g of species B are initially in the Pond system.

GoldSim calculates mass transport so it determines the Species mass in the Cell Pathway. Concentration is then derived as the Species mass / volume for fluid and Species mass / mass for solids.

Species A decays so the total mass in the closed pond system decreases over time. Species B is not initially present and only forms from ingrowth so its mass starts at 0 and increases over time.

Species A decays so the total mass in the closed pond system decreases over time but the partitioning ratio between water and sediment is constant. Species B does not partition so it is only found in the water as a result of decay of species A.

Note that if this were not a closed pond system, it might not make sense to simulate equilibrium partitioning. If there is appreciable flow through the pond, then the flow rate might be large enough that you cannot assume that all of the mass immediately separates to the individual media according to the "equilibrium" ratio. In other words, if you have appreciable flow it is unlikely that there will be "time" for an equilibrium state to be reached in terms of partitioning.

To Open the Model File:

1. Start GoldSim
2. Click on the File and select Open Example...
3. Browse to General Examples --> Contaminant Transport Examples
4. Select the file called Cell1_PartitionDecayIngrowth.gsm