User's guide of Proceessing Modflow 5.0

42 Processing Modflow
< Check simulation results and produce output
During a transport simulation, MOC3D writes a detailed run record to the file
path\MOC3D.LST, where path is the folder in which your model data are saved. MOC3D saves
the simulation results in various files, which can be controlled by choosing MOC3D < Output
Control... from the Models menu.
To check the quality of the simulation results, mass balance calculations are performed and
saved in the run record file. The mass in storage at any time is calculated from the
concentrations at the nodes of the transport subgrid to provide summarized information on the
total mass into or out of the groundwater flow system. The mass balance error will typically
exhibit an oscillatory behavior over time, because of the finite-difference approximation and the
nature of the method of characteristics. As discussed in Konikow et al. (1996), as long as the
oscillations remain within a steady range, not exceeding about ±10 percent as a guide, then the
error probably does not represent a bias and is not a serious problem. Rather, the ocillations only
reflect the fact the mass balance calculation is itself just an approximation.
Using Presentation you can generate contour maps of the calculated concentration. Fig.
2.34 shows the calculated concentration at 3 years in the third layer (simulation
time=9.467E+07 seconds).
To generate the breakthrough curves, choose Graphs < Concentration Time < MOC3D
from the Tools menu. Click on the Plot flags of the Boreholes table until they are set to (Fig.
2.35).
Fig. 2.34 Simulated concentration at 3 years in the third layer
2.2.2 Perform Transport Simulation with MOC3D