A chemical source can be assigned in a number of ways, for example: as a zone representing a continuous source (mass is continuously added at a location) or as an instantaneous source (all mass is added “at once”); from an injection well, from a head-dependent source/sink (e.g., a polluted lake or drain), or from the surface with a prescribed rate of infiltration (recharge).
We will add a zone feature and assign it as a surface source with an infiltration rate of 4 inch/year and a source concentration of 2000 ppm. To do this, we go to Conceptual Modeling Tools, then Zones, and then click the ZoneRec. Draw a rectangular zone in the same location as the particle zone that was used in the last simulation. Click ‘SaveShape’ to open the Zone Attributes menu for the newly added zone, and then navigate to the Sources and Sinks Prescribed tab (see Figure 66). Check the box next to ‘Recharge – Quantity and Quality’, and enter a value of 4 in the text field next to ‘Constant’. This is the prescribed rate of infiltration (units: inch/year). In the text field next to ‘Conc’, enter a value of 2000 (units: ppm). This is the source concentration. Note that it does not change with time, although it is possible to make the source concentration vary with time.