Modeling Expected Solute Concentration in Randomly Heterogeneous Flow Systems with Multicomponent Reactions

Abstract

Many environmental problems require assessment of extensive reaction systems within natural subsurface flow systems exhibiting large physical and biogeochemical heterogeneity. We present an approach to couple stochastic advective-reactive modeling of physical solute transport (LaSAR) with the geochemical model PHREEQC for modeling solute concentrations in systems with variable flow velocity and multicomponent reactions. PHREEQC allows for general and flexible quantification of a multitude of linear and nonlinear geochemical processes, while LaSAR efficiently handles field-scale solute spreading in stochastic heterogeneous flow fields. The combined LaSAR-PHREEQC approach requires very modest computational efforts, thereby allowing a large number of reactive transport problems to be readily assessed and facilitating handling of quantifiable uncertainty in environmental model applications. Computational efficiency and explicit handling of field-scale dispersion without introduction of excessive fluid mixing that may impair model results are general advantages of the LaSAR compared with alternative solute transport modeling approaches. The LaSAR-PHREEQC approach is restricted to steady or unidirectional flow fields, and our specific application examples are limited to homogeneous reaction systems without local or transverse dispersion-diffusion, although these are not general methodological limitations. As a comprehensive application example, we simulate the spreading of acid mine drainage in a groundwater focusing on Zn2+ and including relevant, major-component geochemistry. Model results show that Zn2+ may be substantially attenuated by both sorption and precipitation, with flow heterogeneity greatly affecting expected solute concentrations downstream of the mine waste deposit in both cases.

The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment

“…The advective travel times of dissolved carbon along subsurface transport pathways to the stream network reflect the purely physical rates of advection by the variable mean pore water velocity along and among these pathways (see the travel time-based modeling approaches of both conservative and reactive solute transport in Destouni and Graham, 1995;Eriksson and Destouni, 1997;Simic and Destouni, 1999;Malmström et al, 2004;Darracq et al, 2009;). We conceptualize the whole subsurface flow domain of active carbon release as a shallow and deeper flow domain.…”

“…942 S. W. Lyon et al: Relationship between subsurface hydrology and dissolved carbon fluxes The net effect of these opposing feedback mechanisms depends on the rates of respiration and weathering relative to the DOC and DIC mass transport rates along the different pathways of subsurface water flow. In order to predict the fates of solutes, the transport time of water and solutes along the diverse flow pathways through a catchment must be quantified (Destouni and Graham, 1995;Simic and Destouni, 1999;Kirchner et al, 2001;Malmström et al, 2004;Darracq et al, 2009;. Field-based identification of flow pathways and quantification of the travel time of water along such flow pathways, however, is difficult both in terms of collection of appropriate data and in terms of interpretation.…”

Diffuse hydrological mass transport through catchments: scenario analysis of coupled physical and biogeochemical uncertainty effects

“…McGuire et al, 2005;Destouni et al, 2010;Beven, 2010;McDonnell et al, 2010) -the variability of biogeochemical processes and their combination and cross-correlation with the physical mass transport along the different flow and transport pathways (e.g. Malmström et al, 2004Malmström et al, , 2008Darracq and Destouni, 2007;Cunningham and Fadel, 2007;Jardine, 2008) -the errors of mass transport measurements implied by the chosen measurement methods and the coverage gaps between the chosen measurement points in time and space (e.g. Hannerz and Destouni, 2006;Beven, 2006;Jarsjö and Bayer-Raich, 2008;Destouni et al, 2008) -the chosen model resolutions and possible neglect of potentially important contributing mass transport processes at different scales (e.g.…”

Propagation of water pollution uncertainty and risk from the subsurface to the surface water system of a catchment

“…Such travel time-based, Lagrangian stochastic approaches have been applied to solute transport through subsurface water systems (soil water, groundwater; e.g. Shapiro and Cvetkovic, 1988;Destouni, 1992;Cvetkovic and Dagan, 1994;Destouni and Graham, 1995;Simmons et al, 1995;Yabusaki et al, 1998;Foussereau et al, 2001;Tompson et al, 2002; Malmström et al, 2004) and catchments (Simic and Destouni, 1999;Botter et al, 2005). The travel time pdfs that must be quantified in these approaches are commonly unknown and approximated by assuming some common pdf type (e.g.…”

“…This coupled Lagrangian stochastic advective-reactive (LaSAR) modelling approach can be used for quantifying the transport of reactive pollutants in terms of both expected transport (e.g. Destouni and Graham, 1995;Malmström et al, 2004) and transport variance (e.g. Destouni, 1992;Andricevic and Cvetkovic, 1996;Destouni and Graham, 1997;Andersson and Destouni, 2001;Baresel and Destouni, 2007).…”