A Lagrangian approach to solve Multicomponent reactive transport

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XVIII International Conference on Water Resources
CMWR 2010
J. Carrera (Ed)
CIMNE, Barcelona 2010
A LAGRANGIAN APPROACH TO SOLVE MULTICOMPONENT
REACTIVE TRANSPORT IN COMPLEX GEOLOGICAL
ENVIRONMENTS
Paolo Trinchero*, Jorge Molinero Huguet*, Joaquin Salas Navarro* and Àngels Piqué *
*
Amphos XXI Consulting S.L.
Passeig de Garcia i Faria, 49-51, 1º-1ª - E08019 Barcelona, Spain
e-mail: [email protected], web page: http://www.amphos21.com/
Summary. When dealing with reactive transport problems in complex geological systems
modelers have usually to adopt a compromise either choosing to describe in detail the
geochemical reactions at the expense of a rigorous treatment of the hydrogeological processes
or carrying out complex mechanistic descriptions of subsurface flow while linearizing
geochemical processes with simplified Kd-based simulations (the blanket leaves the shoulders
uncovered). We present a streamline-based framework where the heterogeneity of the flow
velocity field is captured using a Lagrangian approach. Multicomponent reactions are then
explicitly solved along one single 1D streamline for the case of geochemical homogeneity
(LaSAR-PHREEQC, Malmstrom et al., 2009 ) or the entire set of streamlines for the case of
geochemical heterogeneity (FASTREACT), thus avoiding the computational burden of
solving hundreds of thousands speciation calculations in complex 3d grids. An application of
the framework is presented where we evaluate the effects of an hypothetical escape of
radionuclides from a deep geological repository. The probability density functions (pdf ) of
the concentration of the selected set of radionuclides (Sr, Cs, U and Ra) at the outlet of each
streamline allow to explicitly account for the uncertainty due to flow variability as well as to
infer effective Kd parameters.
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