### Abstract

Mass transfer, mixing, and therefore reaction rates during transport of solutes in porous media strongly depend on dispersion and diffusion. In particular, transverse mixing is a significant mechanism controlling natural attenuation of contaminant plumes in groundwater. The aim of the present study is to gain a deeper understanding of vertical transverse dispersive mixing of reaction partners in saturated porous media. Multitracer laboratory experiments in a quasi two-dimensional tank filled with glass beads were conducted and transverse dispersion coefficients were determined from high-resolution vertical concentration profiles. We investigated the behavior of conservative tracers (i.e., fluorescein, dissolved oxygen, and bromide), with different aqueous diffusion coefficients, in a range of grain-related Peclet numbers between 1 and 562. The experimental results do not agree with tie classical linear parametric model of hydrodynamic dispersion, in which the transverse component is approximated as the sum of pore diffusion and a compound-independent mechanical dispersion term. The outcome of the multitracer experiments clearly indicates a nonlinear relation between the dispersion coefficient and the average linear velocity. More importantly, we show that transverse mechanical dispersion depends on the diffusion coefficient of the compound, at least at the experimental bench-scale. This result has to be considered in reactive-transport models, because the typical assumption that two reactants with different aqueous diffusive properties are characterized by the same dispersive behavior does not hold anymore.

Original language | English |
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Journal | Environmental Science & Technology (Washington) |

Volume | 44 |

Issue number | 2 |

Pages (from-to) | 688-693 |

Number of pages | 6 |

ISSN | 0013-936X |

DOIs | |

Publication status | Published - 2010 |

Externally published | Yes |

### Keywords

- Chemistry (all)
- Environmental Chemistry
- Concentration profiles
- Conservative tracers
- Contaminant plume
- Diffusion Coefficients
- Diffusive properties
- Dispersion coefficient
- Dispersive behaviors
- Dispersive mixing
- Glass bead
- High resolution
- Hydrodynamic dispersions
- Laboratory experiments
- Linear parametric models
- Linear velocity
- Mechanical dispersion
- Multi-tracer experiments
- Multitracer
- Natural attenuation
- Nonlinear relations
- Reaction partners
- Saturated porous media
- Transport models
- Transverse dispersion
- Transverse mixing
- Boltzmann equation
- Diffusion
- Dissolution
- Dissolved oxygen
- Experiments
- Fluid dynamics
- Groundwater
- Groundwater pollution
- Hydrodynamics
- Hydrogeology
- Porous materials
- Reaction rates
- Dispersions
- bromide
- dissolved oxygen
- fluorescein
- ground water
- diffusion
- dispersion
- flow modeling
- groundwater pollution
- hydrodynamics
- mass transfer
- mixing
- plume
- porous medium
- reaction kinetics
- solute transport
- tracer
- article
- chemical reaction
- diffusion coefficient
- experiment
- laboratory test
- water contamination
- Bromides
- Chemistry Techniques, Analytical
- Fluorescein
- Mechanics
- Microspheres
- Oxygen
- Physicochemical Processes
- Porosity
- Solutions
- ENGINEERING,
- ENVIRONMENTAL
- POROUS-MEDIA
- REACTIVE TRANSPORT
- PACKED-BEDS
- BIODEGRADATION
- COEFFICIENTS
- DIFFUSION
- NETWORK
- FLOW
- dispersion coefficient
- groundwater
- hydrodynamic transverse dispersion
- mechanical transverse dispersion
- quasi two-dimensional tank
- reaction rate
- bromide 24959-67-9
- contaminant pollutant, water pollutant
- fluorescein 2321-07-5
- porous media
- 04500, Mathematical biology and statistical methods
- 10060, Biochemistry studies - General
- 10515, Biophysics - Biocybernetics
- 37015, Public health - Air, water and soil pollution
- Computational Biology
- linear parametric model mathematical and computer techniques
- multitracer laboratory experiment laboratory techniques
- Models and Simulations
- Pollution Assessment Control and Management
- 2321-07-5 Fluorescein
- S88TT14065 Oxygen
- PLUMES (Fluid dynamics)

## Cite this

Chiogna, G., Eberhardt, C., Grathwohl, P., Cirpka, O. A., & Rolle, M. (2010). Evidence of Compound-Dependent Hydrodynamic and Mechanical Transverse Dispersion by Multitracer Laboratory Experiments.

*Environmental Science & Technology (Washington)*,*44*(2), 688-693. https://doi.org/10.1021/es9023964