Enhancement of dilution and transverse reactive mixing in porous media: Experiments and model-based interpretation

Massimo Rolle, Christina Eberhardt, Gabriele Chiogna, Olaf A. Cirpka, Peter Grathwohl

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Transport and natural attenuation of contaminant plumes in groundwater are often controlled by transverse dispersion. The extent of mixing between dissolved reaction partners at the fringe of a plume determines its length and depends strongly on the groundwater flow field. Transient flow conditions as well as the focusing of the flow in high-permeability zones may enhance transverse mixing of dissolved species and, therefore, create favorable conditions for the natural attenuation of contaminant plumes. The aim of the present study is to experimentally test the influence of these processes on solute mixing and to directly compare the results with those under analogous homogeneous and steady-state conditions. We have performed conservative and reactive tracer experiments in a quasi two-dimensional tank filled with glass beads of different sizes. The experiments have been carried out in both homogeneous and heterogeneous porous media under steady-state and transient (i.e. oscillating) flow fields. We used fluorescein as conservative tracer; whereas an alkaline solution (NaOH) was injected into ambient acidic water (HCl) in the reactive experiments. A pH indicator was added to the reacting solutions in order to visualize the emerging plume. We simulated the laboratory experiments with a numerical model and compared the outcomes of the model with the measured concentrations at the outlet of the tank and with the observed tracer plumes. Spatial moments, a newly defined flux-related dilution index, the product mass fluxes and the reaction enhancement factors were calculated to quantify the differences in mixing and reaction extent under various experimental conditions. The results show that flow focusing in heterogeneous porous media significantly enhances transverse mixing and mixing-controlled reactions, whereas temporally changing flow fields appear to be of minor importance. (C) 2009 Elsevier B.V. All rights reserved.
Original languageEnglish
JournalJournal of Contaminant Hydrology
Volume110
Issue number3-4
Pages (from-to)130-142
Number of pages13
ISSN0169-7722
DOIs
Publication statusPublished - 2009
Externally publishedYes

Keywords

  • Environmental Chemistry
  • Water Science and Technology
  • Laboratory experiments
  • Mixing
  • Numerical modeling
  • Reactive transport
  • Transverse dispersion
  • Acidic water
  • Alkaline solutions
  • Conservative tracers
  • Contaminant plume
  • Different sizes
  • Enhancement factor
  • Experimental conditions
  • Favorable conditions
  • Flow focusing
  • Glass bead
  • Heterogeneous porous media
  • Mass flux
  • Mixing-controlled reaction
  • Model-based
  • Natural attenuation
  • Numerical models
  • PH indicator
  • Porous Media
  • Reaction partners
  • Reactive mixing
  • Reactive tracer
  • Spatial moment
  • Steady-state condition
  • Transient flow conditions
  • Transverse mixing
  • Dispersions
  • Dissolution
  • Flow fields
  • Groundwater
  • Groundwater flow
  • Groundwater pollution
  • Hydrochloric acid
  • Hydrogeology
  • Porous materials
  • Tanks (containers)
  • Experiments
  • fluorescein
  • hydrochloric acid
  • sodium hydroxide
  • dilution
  • experimental study
  • flow field
  • groundwater
  • laboratory method
  • mixing
  • numerical model
  • pollutant transport
  • porous medium
  • reactive transport
  • tracer
  • article
  • controlled study
  • mathematical model
  • particle size
  • pH
  • pollution transport
  • porosity
  • priority journal
  • solute
  • steady state
  • water contamination
  • Environmental Monitoring
  • Models, Theoretical
  • Water Movements
  • ENVIRONMENTAL
  • GEOSCIENCES,
  • WATER
  • TRANSIENT GROUNDWATER-FLOW
  • DISPERSION COEFFICIENTS
  • BIODEGRADATION PROCESSES
  • HYDRAULIC CONDUCTIVITY
  • CONTAMINATED AQUIFER
  • NATURAL ATTENUATION
  • PLUME LENGTHS
  • STEADY-STATE
  • TRANSPORT
  • FRINGE
  • ambient acidic water
  • porous media
  • steady-state condition
  • transport attenuation
  • transverse dispersion
  • sodium hydroxide 1310-73-2
  • 07502, Ecology: environmental biology - General and methods
  • Environmental Sciences
  • Ecology

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