Contaminant back-diffusion from layered aquitards subjected to barrier-controlled source zones

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Low-permeability aquitards act as persistent contaminant sources, complicating groundwater remediation.
• Understanding contaminant mass exchange between aquitards and aquifers is crucial for effective site management.

Purpose of the Study:

• To develop and validate a novel two-dimensional (2D) back-diffusion model for contaminant release from aquitards post-source isolation.
• To investigate the impact of source zone characteristics and aquitard heterogeneity on contaminant transport.

Main Methods:

• Developed a 2D multilayer back-diffusion model incorporating source decay and diffusion-sorption processes.
• Derived exact analytical solutions using finite cosine transform, Duhamel Theorem, separation of variables, and transfer matrix methods.

Main Results:

• The 2D model demonstrates that previous 1D models overestimate aquitard contaminant concentrations and back-diffusion risks.
• Source zone width, concentration, and aquitard heterogeneity significantly influence plume trailing time.

Conclusions:

• The 2D model provides a more accurate assessment of contaminant storage and release from aquitards.
• This research enhances the understanding of aquifer contamination mechanisms beyond isolated source zones, informing remediation efforts.