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Hydrodynamic control of retention in heterogeneous aquifers and fractured rock
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis, fluid flow and solute transport in heterogeneous aquifers and particularly in frac-tured rock have been investigated using Lagrangian Stochastic Advective-Reaction (LaSAR) framework. The heterogeneity of the aquifer structure or fracture configuration, as well as the various reaction/retention processes have been considered in the modelling approach. Advection and retention processes are considered to be the dominant transport processes. Monte-Carlo simulation results for transport of nonreactive tracers in 2D generic heterogeneous aquifers indicate that the travel time τ can be well approximated by a lognormal distribution up to a relative high degree of heterogeneity of the aquifers. Comparison between the Monte-Carlo simulation results and the results of first-order approximation reveals that the analytical solutions of the statistical moments of τ are valid only when the variability of the aquifer properties is small. For reactive tracers, Monte-Carlo simulations have been conducted by accounting for spatial variability of both hydraulic conductivity and one sorption parameter simultaneously. The simulation results indicate that the reaction flow path μ is a nonlinear function of distance for shorter distance, linear function for longer distance, and also that μ and τ are well correlated over the considered parameter range. The parameter β, which is purely determined by the flow condi-tions, quantifies the hydrodynamic control of retention processes for transport of tracers in frac-tures. Numerical simulations have been performed to study the statistical properties of the pa-rameter β, travel time τ and flow rate Q in a single heterogeneous fracture and in a sequence of fractures. The results of Monte-Carlo simulations indicate that the parameter β and τ are corre-lated with a power-law relationship β ∼ τm. The correlation between β and the flow rate Q have also been studied and an inverse power-law relationship β ∼ Q-m is proposed. The establishment of these relationships provides a link between the parameter β and measurable parameters τ (or Q).

The LaSAR approach has been applied for prediction, evaluation and interpretation of the results of a number of tracer tests (TRUE-1, TRUE Block Scale and TRUE Block Scale Continuation) conducted by SKB at the Äspö site for tracer transport in fractures. The breakthrough curves may be predicted reasonably well, provided that the retention parameters, boundary conditions and hydraulic properties of the domain are given. The evaluation of TRUE tests indicates that the retention occurs mainly in the rim zone on site characterization time scales, while on the per-formance assessment time scale, diffusion and sorption in the unaltered rock matrix are likely to become dominant retention mechanisms.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1025
Keyword [en]
Aquifer, Fracture, groundwater, First-order solution, Monte-Carlo simulation, Nu-clear waste, Heterogeneity, Retention processes, Matrix diffusion, Prediction, Evaluation, Travel time, Flow rate;
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-496ISBN: 91-7178-199-4 (print)OAI: oai:DiVA.org:kth-496DiVA: diva2:14223
Public defence
2005-11-29, Sal M2, Brinellvägen 64, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
List of papers
1. Analysis of nonlinear effects on tracer migration in heterogeneous aquifers using Lagrangian travel time approach
Open this publication in new window or tab >>Analysis of nonlinear effects on tracer migration in heterogeneous aquifers using Lagrangian travel time approach
1996 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 32, no 6, 1671-1680 p.Article in journal (Refereed) Published
Abstract [en]

Advective transport in a heterogeneous two-dimensional aquifer is simulated and quantified by the statistical moments of tracer travel time and transverse displacement. These moments depend on the statistics of the Lagrangian velocity given as a function of space rather than time. A comparison is made with first-order results that appear to be robust for log transmissivity variance at least up to 1. Lagrangian statistics for travel time clearly expose a few essential features of nonlinear transport: nonstationary distribution and the increasing integral scale of the Lagrangian velocity. These reflect the tendency of streamlines to concentrate into relatively few flow paths ('preferential flow') for increasing log transmissivity variance. Two simple empirical relationships are identified that in combination with first-order results for the flow capture the main features of nonlinear transport. The proposed methodology can readily be generalized for analyzing advective transport under more complex flow conditions and for establishing relatively simple analytical models for estimating solute mass flux in heterogeneous aquifers.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8788 (URN)
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
2. Contaminant transport in aquifers with spatially variable hydraulic and sorption properties
Open this publication in new window or tab >>Contaminant transport in aquifers with spatially variable hydraulic and sorption properties
1998 (English)In: Proceedings of the Royal Society of Edinburgh. Section A Mathematics, ISSN 0308-2105, E-ISSN 1473-7124, Vol. 454, 2173-2207 p.Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8789 (URN)10.1098/rspa.1998.0254 (DOI)
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
3. Transport of reactive tracers in rock fractures
Open this publication in new window or tab >>Transport of reactive tracers in rock fractures
1999 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 378, 335-336 p.Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8790 (URN)
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
4. Hydrodynamic control of tracer retention in heterogeneous rock fractures
Open this publication in new window or tab >>Hydrodynamic control of tracer retention in heterogeneous rock fractures
2003 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 39, no 5, 1130-1139 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the statistical properties of a Lagrangian random variable beta[T/L], which has been shown to quantify hydrodynamic impact on retention [Cvetkovic et al., 1999], using Monte Carlo simulations of flow and transport in a single fracture. The "local cubic law'' of water flow is generalized to a power law Qsimilar tob(n), where Q is the flow rate, b is the half aperture, and nless than or equal to3. Simulations of flow and particle transport are carried out assuming "local cubic law'' (n=3) and "local quadratic law'' (n=2), and for two typical flow configurations: uniform flow and radially converging flow. We find that beta is related to tau as betasimilar totau(m), where m is dependent on the power n and the configuration of flow and transport. Simulation results for uniform flow indicate that betasimilar totau(n/n-1) for a small source section; as the source section increases, we have the convergence to betasimilar totau. For radially converging flow, we find betasimilar totau for a small source section and a convergence to beta=const for an increasing source section. Simulation results for both flow configurations are consistent with the results for a homogeneous fracture. The results for a homogeneous fracture provide reasonable bounds for simulated beta. The correlation between beta and Q is relatively weak for all cases studied.

Keyword
Flow, Fracture, Matrix diffusion, Retention, Transport
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-8791 (URN)10.1029/2002WR001354 (DOI)000183111100001 ()
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-09-16Bibliographically approved
5. Impact of temperature increase on nuclide transport in crystalline rock on the near field scale
Open this publication in new window or tab >>Impact of temperature increase on nuclide transport in crystalline rock on the near field scale
2004 (English)In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems: Fundamentals, Modelling, Experiments and Applications, Elsevier , 2004, 2, 413-418 p.Chapter in book (Other academic)
Abstract [en]

The TRUE (“Tracer Retention Understanding Experiments”) programme at the Äspö Hard Rock Laboratory (Winberg et al., 2000, 2002) has since 1995 generated a unique database for quantifying retention of radionuclides in crystalline rock on the 5-30m scales. Temperature conditions in the TRUE analysis were about 15°C. In this study, we consider the effect of temperature increase to ca 60°C consistent with conditions after say 1000 years in the rock volume surrounding a KBS-3 type of repository, anticipated to persist over a relatively long time. Temperature elevation will decrease the mean aperture of a conducting fracture by approximately 30%, which in turn will enhance retention. Furthermore, diffusion in the rock matrix will increase at elevated temperatures by approximately factor 4, further enhancing retention. Sorption coefficients are assumed to be unchanged since there is still considerable uncertainty regarding sorption and its change with increasing temperature. We show that elevated temperature on the near field scale enhances nuclide retention, thereby providing an additional safety margin.

Place, publisher, year, edition, pages
Elsevier, 2004 Edition: 2
Series
Elsevier Geo-Engineering Book Series
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8792 (URN)10.1016/S1571-9960(04)80076-4 (DOI)2-s2.0-77957030590 (Scopus ID)
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved
6. Impact of internal heterogeneity for tracer transport in fractured rock
Open this publication in new window or tab >>Impact of internal heterogeneity for tracer transport in fractured rock
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8793 (URN)
Note
QC 20100624Available from: 2005-11-22 Created: 2005-11-22 Last updated: 2010-06-24Bibliographically approved

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