It is possible to describe a catchment area in consideration of advection- and dispersion-/ diffusion processes. Thus also the local heterogeneities can be simulated with the dispersion term which are not or only limited ascertainable with conventional methods of velocity tracing.

The base of this approach is described in detail in Uffink, F., Application of Kolmogorovs backward equation in random walk simulations of groundwater contaminant transport; Contaminat Transport in Groundwater, Kobus & Kinzelbach, 1986 and Wilson, J.L. and J. Liu, Backward particle tracking to find the source of pollution in waste management. Waste Management: From Risk to Reduction, 1995.

If the concentration in the well is given with 1.0 the probabilities of the arriving particle at the well will be calculated as a concentration value. With the presentation of isoconcentration areas from 0.05 to 1.0 the 95%-propability of the arrival of a particle at the withdrawal well will be calculated.

The figures show a 3D example. Here the two aquifers are separated by a groundwater aquitard. The withdrawal wells deliver from the bottom aquifer. The 50 day area is shown in the vertical and horizontal section:

 

Horizontal flow

 

Vertical flow

 

A detailed description of the procedure of inverted flow is beyond the scope of this manual. During a training session the calculation of transport processes with inverted flow can be discussed by request.