4.1.3  Overland Flow (Runoff)

The overland flow loss process is assumed to occur by runoff from the surface of the pond/surface impoundment.  Because we are assuming that the aqueous solution, the suspended sediment, and the suspended NAPL-phase globules (if present) all are lost from the pond in the runoff process, the mass flux equation for loss from the pond by overland flow (either alone or simultaneous with the other processes) can be expressed as



where Q_over  total flux of aqueous solution, sediment, and NAPL globules as pond runoff (cm³ yr^-1).

Note that in Equation 4.11, Q_over is not just the volumetric flux of water (or aqueous solution) leaving the pond as runoff, but rather it is the total volumetric flux of aqueous solution, sediment, and NAPL-phase globules (if present) leaving the pond as runoff.

 Substituting Equation 4.1 into Equation 2.2, to obtain a specific expression for the overall total contaminant concentration in a pond/surface impoundment source zone, and then substituting the resulting expression into Equation 4.11, we can rewrite the mass flux equation for loss from the pond by overland flow (either alone or simultaneous with the other processes) as