Gravity-driven fingers in fractures: experimental study and dispersion analysis by moment method for a point-source...

Area of Science:

• Environmental Science
• Hydrogeology
• Fluid Dynamics

Background:

• Contaminant transport in fractured media is critical for groundwater protection.
• Understanding plume behavior in fractures informs risk assessment and remediation strategies.
• Previous models often simplify the complex dynamics of dense contaminant plumes.

Purpose of the Study:

• To experimentally investigate the behavior of dense contaminants injected from a point source in a fracture.
• To analyze the factors influencing plume propagation patterns, specifically one- and two-finger plumes.
• To compare experimental dispersion data with theoretical models.

Main Methods:

• Utilized a transparent Hele-Shaw cell (0.5 mm aperture) as an experimental model.
• Employed Laser Induced Fluorescence (LIF) for precise concentration measurements of the contaminant plume.
• Applied spatial and time moment methods to interpret experimental dispersion.

Main Results:

• Observed both one- and two-finger plume propagation patterns.
• Identified injection flow-rate and contaminant concentration as key factors in plume finger separation.
• Experimental dispersivities closely matched theoretical predictions from a density-dependent dispersion tensor at later times.

Conclusions:

• The separation of contaminant plumes into two fingers is significantly influenced by the pre-asymptotic dispersion tensor behavior.
• Longitudinal macro-dispersion exhibits asymptotic behavior, indicating predictable plume spread over distance.
• Experimental findings validate theoretical models for contaminant transport in fractures under specific conditions.