SWMM can simulate the generation, inflow and transport of any number of user-defined
pollutants.
The input parameters for the pollutant are listed in the table below.
Co-pollutants can also be defined in SWMM. For example, pollutant X can have a co-pollutant Y, meaning that the runoff concentration of X will have some fixed fraction of the runoff concentration of Y added to it.
Pollutant buildup and washoff from subcatchment areas are determined by the land uses assigned to those areas. Input loadings of pollutants to the drainage system can also originate from external time series inflows as well as from dry weather inflows.
| Field | Description |
| Name | User-assigned pollutant name. |
| Units | The concentration units (mg/L, ug/L, or #/L (counts/L)) in which the pollutant concentration is expressed. |
| Rain Concentration | Concentration of the pollutant in rain water (concentration units). |
| GW Concentration | Concentration of the pollutant in ground water (concentration units). |
| Initial Concentration | Concentration of the pollutant throughout the conveyance system at the start of the simulation. |
| I&I Concentration | Concentration of the pollutant in any Infiltration/Inflow (concentration units). |
| DWF Concentration | Concentration of the pollutant in any dry weather sanitary flow (concentration units). This value can be overridden for any specific node of the conveyance system by editing the node's Inflows property. |
| Decay Coefficient | First-order decay coefficient of the pollutant (1/days). |
| Snow Only | YES if pollutant buildup occurs only when there is snow cover, NO otherwise (default is NO). |
| Co-Pollutant | Name of another pollutant whose runoff concentration contributes to the runoff concentration of the current pollutant. |
| Co-Fraction | Fraction of the co-pollutant's runoff concentration that contributes to the runoff concentration of the current pollutant. |
An example of a co-pollutant relationship would be where the runoff concentration of a particular heavy metal is some fixed fraction of the runoff concentration of suspended solids. In this case suspended solids would be declared as the co-pollutant for the heavy metal.