Accounting for Reactive Processes

This assumption, however, is a reasonable approximation even for situations where the distribution of physico-chemical parameters is heterogeneous to some extent, in particular if the scale of physico-chemical heterogeneity is considerably smaller than the transport distance or if inter-connectivity of high permeable areas is low, i.e. all fluid particles reside on their way from input to control siuface approximately the same time in low as well as in high permeability areas. This is demonstrated by Peter et al. (chapter 14) by means of a comparison of SMART and the well-known transport code MT3D (Zheng, 1990). 

If large-scale physico-chemical heterogeneities are present and the individual solute particles encounter quite different physicochemical properties of the aquifer material along their flowpaths, reactive transport must be computed explicitly in terms of r along each and every streamtube (see below and Thiele et al., 1995A, 

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