IGW-NET allows the user to specify spatial variables to any of the shapes defined in the original groundwater model (polygon, zones, lines, wells, etc).
How to use it:
Select a feature and "Edit Props" to assign spatial properties to a species. This includes parameters like initial concentrations, diffusion coefficients, decay coefficients, etc. If shapes were not explicitly named when the groundwater model was built they may have names like "GMPolygon0". These shape names can be inspected/changed in the original groundwater model (Other tools > Utilities > Geometry unlocked > click on shape).