The Three-dimensional Reactive Transport Modelling Approach

2 The Three-dimensional Reactive Transport Modelling Approach 

The concept and the basic steps of the reactive transport simulation approach are summarized in Fig. 3.1. At first, lithofacies types, i.e. aquifer material categories are assigned to aquifer material samples obtained from drill cores. Each facies type is characterized with respect to representative hydraulic and hydrogeochemical properties. Then, generally based on a geostatistical analysis, a spatial distribution of lithofacies types is generated. Since each lithofacies type has characteristic hydraulic and 

Finite-dlffeience model grid and claMification into different lithofacies 

Deconiposiicin of facies matedal into ithoconifiDneniB (LC) and aai size ttactiDns (GS) 

In the following, the individual steps of the facies-based reactive transport modelling approach are described more detailed. 

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Figure 3.1 Concept and basic steps of the three-dimensional reactive transport modelling approach.

SMART is applicable if integral information on contaminant behaviour in groundwater is sufficient. If point information is needed a conventional FD or FE model has to be used. Although it is obvious that the streamtube approach is not as flexible as real 3D models , decoupling of conservative transport and physico-chemical processes allow to model three-dimensional contaminant transport in a convenient and computationally efficient way, especially if only one representative streamtube must be modelled. Computation times, as observed by Peter et al. (chapter 14) are much lower compared to MT3D simulations. It should also be mentioned, that the streamtube approach possesses some advantages compared to real 3D models even if each and every streamtube has to be modelled by means of a numerical model in order to evaluate F. Since only one dimensional advective-reactive transport must be modelled, numerical solutions based on discrete or mechanistical approaches, free of numerical dispersion, can be applied. In SMART this is done by a so-called parceltracking approach where contaminant transport is described by means of a continuous series of water volumes ( parcels ) as described in Finkel et al. (1998). 

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