Integrated global random walk model for reactive transport in groundwater adapted to measurement spatio-temporal scales

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New Global Random Walk (GRW) algorithms, stable and free of numerical diffusion, will be designed and implemented to solve flow and reactive transport equations for heterogeneous groundwater systems. To prevent the occurrence of the interpolation errors, an integrated GRW solver will be developed, which computes velocities and concentrations on the same regular lattice. Coarse Grained (CG) space-time averages over the trajectories of the computational particles describing concentrations of reacting chemical species in GRW simulations will be used to obtain a continuous description ofthe transport process. Since the averaging procedure reduces the variability of the simulated concentrations, a relatively small number of MC runs could be enough to obtain statistical inferences, while accounting for the effect of space-time scales of the hydrological observations. Furthermore, local balance equations for CG space-timeaverages can be used to compute upscaled diffusion coefficientsand reaction terms.