The setting of water quality in outflow

I have a question about the modelling of water quality, if I set the concentration of water quality in the outflow which is set as negative number , whether the setting of water quality in outflow make sense or not?
If I want to get the outflow with certain concentration, how should I set the model.


If you have outflow boundary in your model, then the outgoing concentration is calculated by the model internally. You have control about the incoming concentration / inflow into the boundary, however, you cannot control the outgoing concentration in the EFDC model. If you specify the pressure boundary / specified elevation boundary, then you can specify the concentration but that concentration would only be used when the flow is coming into the domain.