Non-reactive solute movement through saturated laboratory samples of undisturbed stratified sandstone

Abstract

There has been much recent work on developing models of non-reactive solute migration in saturated stratified porous media. Almost all experimental results against which the models have been tested have been obtained using artificial media. The aim of the present study is to test the models against data from naturally stratified media. In this paper we report the results of the experiments carried out on samples of laminated, intact, saturated Triassic sandstone from the UK. Column experiments were performed at steady flow rates using samples with flow either parallel or perpendicular to the lamination. For flow parallel to the lamination, the breakthrough curves were asymmetrical. They were generally characterized by early breakthrough and tailing. Asymmetry and tailing increased with increasing flow rate. Column experiments in which flow was interrupted showed the presence of physical non-equilibrium. For flow perpendicular to the lamination the breakthrough curves were symmetrical. Simultaneous use of bromide and amino-G-acid, conservative tracers having very different diffusion coefficients, demonstrated the significance of diffusion particularly when the flow is parallel to the lamination. Thinsection analysis, dye staining and positron emission projection imaging (PEPI) techniques were used to study the spatial variations in hydraulic properties in the samples. Thinsection analysis indicated that the thickness of individual layers, each of different porosity and grain size, varies from less than 1 mm to several millimetres and occasionally exceeds 1 cm. The dye and PEPI experiments also identified stratification of flow when the flow is parallel to the lamination, but in the latter case the most obvious stratification was at a larger scale than for the former. No preferential flow was found for samples with flow perpendicular to the lamination. It is concluded that the dominant process in solute migration in the sandstone samples is stratification that is, at least, at two scales, a process which will result in a fractionation where two solutes of different diffusion coefficient are present.

Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media

“…diffusive mass transfer between advective and nonadvective water) and chemical (e.g. nonlinear sorption) nonequilibrium processes in soil (Brusseau et al, 1997), determination of nonreactive solute exchange between the matrix porosity and preferential flow paths in fractured shale (Reedy et al, 1996), quantifying the effect of aggregate radius on diffusive timescales in dual porosity media (Cote et al, 1999), numerical modelling of aqueous contaminant release in nonequilibrium flow conditions (Wehrer and Totsche, 2003), empirical modelling of the release of dissolved organic species (Guimont et al, 2005;Ma and Selim, 1996;Totsche et al, 2006;Totsche, 2005, 2009) and heavy metals (Buczko et al, 2004), increasing the efficiency of solute leaching (Cote et al, 2000), empirical modelling of conservative tracer transport in a laminated sandstone core sample (Bashar and Tellam, 2006), and characterising in situ aquifer heterogeneity (Gong et al, 2010). One area where comparatively few studies exist, however, is in characterising the hydraulic properties of aquitards (e.g.…”

Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media

“…diffusive mass transfer between advective and nonadvective water) and chemical (e.g. nonlinear sorption) nonequilibrium processes in soil (Brusseau et al, 1997), determination of nonreactive solute exchange between the matrix porosity and preferential flow paths in fractured shale (Reedy et al, 1996), quantifying the effect of aggregate radius on diffusive timescales in dual porosity media (Cote et al, 1999), numerical modelling of aqueous contaminant release in nonequilibrium flow conditions (Wehrer and Totsche, 2003), empirical modelling of the release of dissolved organic species (Guimont et al, 2005;Ma and Selim, 1996;Totsche et al, 2006;Totsche, 2005, 2009) and heavy metals (Buczko et al, 2004), increasing the efficiency of solute leaching (Cote et al, 2000), empirical modelling of conservative tracer transport in a laminated sandstone core sample (Bashar and Tellam, 2006), and characterising in situ aquifer heterogeneity (Gong et al, 2010). One area where comparatively few studies exist, however, is in characterising the hydraulic properties of aquitards (e.g.…”

Biased Estimation of Groundwater Velocity from a Push-Pull Tracer Test Due to Plume Density and Pumping Rate

“…One of the commonly utilized methods to estimate aquifer hydrogeologic properties is a tracer test, in which nonreactive or reactive tracers are injected into a borehole to generate a breakthrough curve of the injected tracer transporting through the aquifer medium [1][2][3]. Based on the analysis of the obtained breakthrough curves from the tracer test, information about the aquifer geometry, solute transport dynamics, microbial processes, and reactive movement of the tracer can be evaluated [4][5][6][7].…”