Long‐Term Reactive Solute Transport in an Aquitard Using a Centrifuge Model

Timms, Wendy; Hendry, M. Jim

doi:10.1111/j.1745-6584.2008.00441.x

Cited by 22 publications

(18 citation statements)

References 36 publications

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“…A second technical challenge is that laboratory testing typically requires generation of flow through the sample whilst maintaining relevant in situ hydro-geotechnical conditions. One method which has been demonstrated as effective for this purpose is centrifugation, which is increasingly being used for hydraulic and geotechnical testing of low K materials (Hensley and Schofield, 1991;Nimmo and Mello, 1991;Timms et al, 2009;Timms and Hendry, 2008). Moreover, experiments using geotechnical centrifuges with payload capacities exceeding several kilograms can provide the additional benefit of being able to use core samples of representative scale for the overall formation.…”

Section: Introductionmentioning

confidence: 99%

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

Crane

Cuthbert

Timms

2015

Hydrol. Earth Syst. Sci.

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Abstract. We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge-induced flow, no flow and centrifuge-induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite-clay-dominated core samples. All core samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted flow. This is indicative of dual (or multi-)porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (NashSutcliffe model efficiency coefficient was > 0.97 for all samples). In combination, interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media. IntroductionIt is well known that heterogeneities, including biogenic pores/channels, desiccation cracks, fissures, fractures, nonuniform particle size distributions and inter-aggregate pores, are widespread in the subsurface and lead to a range of preferential flow phenomena (Beven and Germann, 1982;Cuthbert et al., 2013;Cuthbert and Tindimugaya, 2010;Flury et al., 1994). The coexistence of a relatively high hydraulic conductivity (K) domain(s) and an impermeable one, often termed dual porosity, results in a non-Fickian breakthrough curve. Solute transport in such systems is often characterised by an early arrival of solutes originating from the more mobile domain (macropores) and a slow approach to the final concentration caused by diffusion into the immobile domain (matrix or microporous network). When fitting breakthrough curves, therefore, it is often difficult to differentiate between contributions from the micro-and macropore transport mechanisms. As a consequence, in recent years there has been much research into the development of effective empirical and modelling techniques to characterise solute transport processes for dual porosity systems. One method investigated has been the use of interruptedflow solute-breakthrough experiments. Amongst the original work on this topic Murali and Aylmore (1980) discussed the influence of nonconstant flow on solute transport in aggregated soil. Brusseau et al. (1989) developed a flowinterruption method for use in measuring rate-controlled sorption processes in soil systems, which was subsequently applied by Koc...

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Section: Introductionmentioning

confidence: 99%

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

Crane

Cuthbert

Timms

2015

Hydrol. Earth Syst. Sci.

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“…Solute breakthrough experiments require longer testing periods of steadystate flow than for permeability testing. For example, Timms and Hendry (2008) and Timms et al (2009) described continuous CP experiments over 90 days to quantify reactive solute transport during several pore volumes (PV) of flow. The comparisons of time required for 1 PV provided in Table 5 illustrate the possible advantages of CP for contaminant flow that may affect the structural integrity of the material.…”

Section: Groundwater Flow At Natural Gradient and Accelerated Conditionsmentioning

confidence: 99%

Accelerated gravity testing of aquitard core permeability and implications at formation and regional scale

Timms¹,

Crane²,

Anderson³

et al. 2015

Preprint

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Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, the extraction of fuels from strata such as coal beds, and the confinement of waste within the earth. The current work demonstrates that relatively rapid and reliable hydraulic conductivity (K) measurement of aquitard cores using accelerated gravity can inform and constrain larger scale assessments of hydraulic connectivity. Steady state fluid velocity through a low K porous sample is linearly related to accelerated gravity (g-level) in a centrifuge permeameter (CP) unless consolidation or geochemical reactions occur. The CP module was custom designed to fit a standard 2 m diameter geotechnical centrifuge (550 g maximum) with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length, and a maximum total stress of ~2 MPa at the base of the core. Formation fluids were used as influent to limit any shrink–swell phenomena which may alter the permeability. Vertical hydraulic conductivity (Kv) results from CP testing of cores from three sites within the same regional clayey silt formation varied (10−7 to 10−9 m s−1, n = 14). Results at one of these sites (1.1 × 10−10 to 3.5 × 10−9 m s−1, n = 5) that were obtained in < 24 h were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses over several weeks within a 30 m clayey sequence. Core scale and in situ Kv results were compared with vertical connectivity within a regional flow model, and considered in the context of heterogeneity and preferential flow paths at site and formation scale. More reliable assessments of leakage and solute transport though aquitards over multi-decadal timescales can be achieved by accelerated core testing together with advanced geostatistical and numerical methods.

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“…The potential of centrifuge modelling has rarely been explored for the purpose described in this study (Kumar, 2006(Kumar, , 2007McKinley et al, 1998;Timms and Hendry, 2008;Shu et al, 2018), being widely used to study failure mechanism of slopes, earth and barriers retaining structures, and for building or bridge foundation (Edelmann et al, 1999;Indrasenan Thusyanthanet al, 2006a, 2006bJessberger and Stone, 1991;Taylor 2003). This research will produce design guidelines enabling the selection and engineering of liner compositions from these materials which maximise contaminant attenuation for appropriate operational timescales (i.e.…”

Section: Introductionmentioning

confidence: 99%

High Attenuation Recycled Materials as landfill liners (the HARM project) – A new concept for improved landfill liner design

Regadío¹,

Cargill²,

Black³

et al. 2020

Preprint

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A new approach in landfill liner design which combines hydraulic containment of leachate with contaminant attenuation to improve the performance of these environmental control systems at landfills is described. The idea is to re-use readily available industrial waste residues (construction and biomass waste) as additives for natural clay liners, wherein the additives have specific properties which enhance the attenuation of contaminants by the mixture. The aim is to (1) evaluate the contaminant attenuation capacity of these mixtures, (2) develop design guidelines to construct liners for waste containment systems and similar applications, and (3) interpret their performance using numerical modelling. This is evaluated in permeation studies using a geotechnical centrifuge, which enables the performance of liner compositions to be tested for representive time-scales (100 years), pressures and temperatures at realistic experimental time-scales of days-weeks in the laboratory. The permeation experiments include liner compositions flushed with leachate to deduce contaminant transport and attenuation mechanisms, followed by rainwater to assess the potential for release of attenuated contaminants. This experimental methodology is illustrated with depth profiles from permeation studies conducted on different clay-additive compositions. The concept will be applicable for liner design at other waste disposal facilities and is a timely improvement which addresses the problem of managing large quantities of industrial residues. Instead of disposal these can be recycled as an additive in host clay to construct these liners, thus conserving natural resources (clay) and reducing construction costs. It also provides an effective and more environmentally sustainable basis to reduce risks from leachate leakage.

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Long‐Term Reactive Solute Transport in an Aquitard Using a Centrifuge Model

Cited by 22 publications

References 36 publications

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

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

Accelerated gravity testing of aquitard core permeability and implications at formation and regional scale

High Attenuation Recycled Materials as landfill liners (the HARM project) – A new concept for improved landfill liner design

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