Simple Mixing

Starting with the simplest assumptions, that the effects of diffusion and dispersion are negligible relative to the effects of advection, the stream may be represented as a plug-flow system. The initial concentration of a pollutant at the point of injection into the stream is calculated from a mass balance:

Eqn. 1

Where:

c is the new concentration (mg/l)
Qw is the flow of wastewater discharged (m3/time)
Cw is the concentration of pollutant in the wastewater (mg/l)
Qr is the flow of receiving water (m3/time)
Cr is the concentration of pollutant in the receiving water (mg/l)

This is the simplest case of representing the spatial and temporal variation of pollution in a system. One possible candidate that could be modeled as a conservative pollutant would be salinity.