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Water Mixing Approach (WMA) for reactive transport modeling
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  • Joaquim Soler-Sagarra,
  • Maarten W. Saaltink,
  • Francesca De Gaspari,
  • Albert Nardi,
  • Jesús Carrera
Joaquim Soler-Sagarra
Associated Unit: Hydrogeology Group (UPC-CSIC)

Corresponding Author:[email protected]

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Maarten W. Saaltink
Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya (UPC)
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Francesca De Gaspari
Technical University of Catalonia
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Albert Nardi
Barcelona Science Technologies S.L.
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Jesús Carrera
Institut de Diagnòstic Ambiental, Barcellona, Spain
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We describe a formulation to solve reactive transport problems. The basic idea is to represent transport as mixing water instead of individual solute concentrations, hence the Water Mixing Approach (WMA) name. This representation simplifies calculations as it decouples transport from chemical calculations. Transport is first solved in terms of water mixing ratios (λ), which is feasible for any transport solution method. Chemical calculations can then be written as reactive mixing calculations, which may be non-linear but local, so that they do not need to iterate with transport. We have implemented the WMA to a mixed Eulerian-Lagrangian method transport solver with streamline-oriented grid and constant travel time between sequential cells (isochronal grid), which is free of numerical dispersion. We test the WMA on two reactive transport cases. First, an existing analytical solution of binary system case is used compared to test accuracy of the using of mixing ratios. Second, a calcite dissolution case compared the WMA to the Direct Substitution Approach to test both accuracy and computational cost (CPU). Results confirm the high accuracy and efficiency (low CPU cost) due decoupling transport and chemical steps, especially for a refined grid was. Transport through highly heterogeneous media remains a challenge, but the definite separation of mixing processes in WMA opens a new path for reactive transport modelling.
Mar 2022Published in Advances in Water Resources volume 161 on pages 104131. 10.1016/j.advwatres.2022.104131