# Lesson 8 - Running the Model and Viewing Results

Now that we have built this simple model, we are ready to run it.

By default, a new GoldSim model defaults to a duration of 100 days with a timestep of 1 day.  For this simple example, we don’t need to change this. Run the model now.

The first result we will look at is the total mass in the pathway.  Left-click on the output port (which will now be green), right-click on Mass_in_Pathway, and select Time History Result:

The result will look like this:

This is obviously not a very interesting result for X.  That species does not decay (and we are not transporting any mass in this simple model) so that the mass stays constant in time. The mass of Y, however, decays with time (with a half-life of 50 days).  In fact, you will note that at 50 days, the mass is exactly half of its initial value.

Now let’s look at the concentration results. Left-click on the output port (which will now be green), right-click on Concentration_in_Water, and select Time History Result:

Notice that this result of concentration versus time is essentially identical (in terms of shape) to the result of mass versus time.  In particular, if you take the mass values and divide them by the volume of water (5 m3), it produces the concentration values we see here.  This is because partitioning onto the Sand has no impact on these results. It is the total (effective) concentration and explicitly includes the mass that is partitioned onto the suspended Sand.  In fact, if the partition coefficients were zero, we would see the exact same result.

Next let’s look at the dissolved concentration result. Left-click on the output port (which will now be green), right-click on Dissolved_Conc_in_Water, and select Time History Result:

Note that this result is different than the total concentration result.  The impact of partitioning is most easily seen by looking at the initial concentration for both species (since one species decays and the other does not).  You will see that in both cases it is lower than in the previous result, since some of the mass is partitioned onto the Sand.  This partitioning has a larger impact on Y than on X (since Y has a larger partition coefficient than X).

Finally, let’s look at the concentration in the Sand. Left-click on the output port (which will now be green), right-click on Concentration_in_Sand, and select Time History Result:

Again, it is easiest to focus on the initial concentration of both species. You will note that both species partition onto the Sand, but the concentration of Y is initially higher (before it decays), since it has a larger partition coefficient than X.

Note: If you had any trouble building this Example, you can find the model by going to the “Examples” subfolder of the “Contaminant Transport Course” folder you should have downloaded and unzipped to your Desktop, and opening a model file named ExampleCT4_Tank.gsm.

In the next Lesson, we will discuss how GoldSim computed these results.