Transverse vertical dispersion in groundwater and the capillary fringe.

Transverse dispersion is the most relevant process in mass transfer of contaminants across the capillary fringe (both directions), dilution of contaminants, and mixing of electron acceptors and electron donors in biodegrading groundwater plumes. This paper gives an overview on literature values of transverse vertical dispersivities alpha(tv) measured at different flow velocities and compares them to results from well-controlled laboratory-tank experiments on mass transfer of trichloroethene (TCE) across the capillary fringe. The measured values of transverse vertical dispersion in the capillary fringe region were larger than in fully saturated media, which is credited to enhanced tortuosity of the flow paths due to entrapped air within the capillary fringe. In all cases, the values observed for alpha(tv) were << 1 mm. The new measurements and the literature values indicate that alpha(tv) apparently declines with increasing flow velocity. The latter is attributed to incomplete diffusive mixing at the pore scale (pore throats). A simple conceptual model, based on the mean square displacement and the pore size accounting for only partial diffusive mixing at increasing flow velocities, shows very good agreement with measured and published data.

[1]  G. Dagan.  Dispersion of a passive solute in non-ergodic transport by steady velocity fields in heterogeneous formations , 1991, Journal of Fluid Mechanics.

[2]  K. Jensen,et al.  Large‐scale dispersion experiments in a sandy aquifer in Denmark: Observed tracer movements and numerical analyses , 1993 .

[3]  A. Valocchi,et al.  An experimental investigation of NAPL pool dissolution enhancement by flushing , 1999 .

[4]  John A. Cherry,et al.  Migration of contaminants in groundwater at a landfill: A case study: 4. A natural-gradient dispersion test , 1983 .

[5]  Michel Quintard,et al.  Calculation of the effective properties describing active dispersion in porous media: from simple to complex unit cells , 2001 .

[6]  J. Delgado,et al.  Lateral dispersion in liquid flow through packed beds at Pem < 1,400 , 2000 .

[7]  Donald R. F. Harleman,et al.  Longitudinal and lateral dispersion in an isotropic porous medium , 1963, Journal of Fluid Mechanics.

[8]  Gary A. Robbins,et al.  Methods for determining transverse dispersion coefficients of porous media in laboratory column experiments , 1989 .

[9]  F. Brockman,et al.  Transport and biodegradation of quinoline in horizontally stratified porous media , 1994 .

[10]  J. Bear.  Dynamics of Fluids in Porous Media , 1975 .

[11]  G. Taylor.  Dispersion of soluble matter in solvent flowing slowly through a tube , 1953, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[12]  D. Ronen,et al.  The Behavior of Groundwater in the Vicinity of the Water Table Evidenced by Specific Discharge Profiles , 1986 .

[13]  G. L. Moltyaner,et al.  Twin Lake Tracer Tests: Transverse dispersion , 1988 .

[14]  M. Blunt,et al.  On the Structure and Flow Processes in the Capillary Fringe of Phreatic Aquifers , 1997 .

[15]  M. Mariño,et al.  Interlayer Diffusive Transfer and Transport of Contaminants in Stratified Formation. I: Theory , 1998 .

[16]  René Therrien,et al.  Simulating transport and removal of xylene during remediation of a sandy aquifer , 1995 .

[17]  P. Saffman,et al.  A theory of dispersion in a porous medium , 1959, Journal of Fluid Mechanics.

[18]  K. Verschueren.  Handbook of environmental data on organic chemicals , 1977 .

[19]  Harihar Rajaram,et al.  Three-dimensional spatial moments analysis of the Borden Tracer Test , 1991 .

[20]  F. Caron,et al.  A large-scale laboratory experiment to determine the mass transfer of CO2 from a sandy soil to moving groundwater , 1998 .

[21]  S. P. Garabedian,et al.  Large-scale dispersive transport in aquifers : field experiments and reactive transport theory , 1987 .

[22]  Peter Grathwohl,et al.  Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics , 1998 .

[23]  J. Delgado,et al.  Measurement of the Coefficient of Transverse Dispersion in Flow Through Packed Beds for a Wide Range of Values of the Schmidt Number , 2001 .

[24]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[25]  G. Dagan,et al.  Concentration fluctuations in transport by groundwater: Comparison between theory and field experiments , 1999 .

[26]  J. H. Dane,et al.  Movement and Remediation of Trichloroethylene in a Saturated Heterogeneous Porous Medium 1. Spill Behavior and initial dissolution , 1999 .

[27]  Eckhard Worch,et al.  Eine neue Gleichung zur Berechnung von Diffusionskoeffizienten gelöster Stoffe , 1993 .

[28]  Rainer Helmig,et al.  Numerical simulation of biodegradation controlled by transverse mixing , 1999 .

[29]  Jacob H. Dane,et al.  Experimental investigation of dense solute plumes in an unconfined aquifer model , 1992 .

[30]  D. Read,et al.  Uranium migration through intact sandstone cores , 1993 .

[31]  James M. Miller.  Dynamics of Chromatography , 1966 .

[32]  K. McCarthy,et al.  Transport of volatile organic compounds across the capillary fringe , 1993 .

[33]  F. Grane,et al.  Measurements of Transverse Dispersion in Granular Media. , 1961 .

[34]  Peter K. Kitanidis,et al.  The concept of the Dilution Index , 1994 .

[35]  P. Saffman,et al.  Dispersion due to molecular diffusion and macroscopic mixing in flow through a network of capillaries , 1960, Journal of Fluid Mechanics.

[36]  P. Kitanidis,et al.  Characterization of mixing and dilution in heterogeneous aquifers by means of local temporal moments , 2000 .

[37]  Evangelos A. Voudrias,et al.  Dissolution of TCE and TCA Pools in Saturated Subsurface Systems , 1994 .

[38]  U. Klose,et al.  Determination of the apparent transverse and axial dispersion coefficients in a chromatographic column by pulsed field gradient nuclear magnetic resonance , 1995 .

[39]  J. Delgado,et al.  Mass transfer from a large sphere buried in a packed bed along which liquid flows , 1999 .

[40]  G. De Josselin De Jong,et al.  Longitudinal and transverse diffusion in granular deposits , 1958 .

[41]  M. Rivett.  Soil‐Gas Signatures from Volatile Chlorinated Solvents: Borden Field Experiments , 1995 .

[42]  R. Gillham,et al.  Effects of solute concentration–dependent surface tension on unsaturated flow: Laboratory sand column experiments , 1999 .

[43]  Brian Berkowitz,et al.  Mass transfer at fracture intersections: An evaluation of mixing models , 1994 .

[44]  James F. Pankow,et al.  Dissolution of dense chlorinated solvents into groundwater. 2. Source functions for pools of solvent , 1992 .