Analytical Model for Volatile Organic Compound Transport in the Coupled Vadose Zone-Groundwater System

Area of Science:

• Environmental Science
• Geoscience
• Chemical Engineering

Background:

• Volatile organic compounds (VOCs) pose risks in subsurface environments.
• Understanding contaminant transport in coupled vadose-saturated zones is crucial for risk assessment.
• The vapor intrusion pathway is a significant concern at contaminated sites.

Purpose of the Study:

• To develop a 3D mathematical model for VOC transport in a coupled vadose-saturated zone system.
• To derive analytical solutions for contaminant fate and transport under specific conditions.
• To assess the impact of interphase mass transfer and back-diffusion on contaminant behavior.

Main Methods:

• Development of a 3D mathematical model incorporating advection, dispersion, and interphase mass transfer.
• Derivation of analytical solutions for the coupled vadose-saturated zone system.
• Evaluation of solutions using numerical Laplace inverse transform.

Main Results:

• The model effectively simulates VOC transport, including mass loading from source zones.
• Back-diffusion from the saturated to the vadose zone was observed, leading to secondary contamination.
• Low contaminant concentrations can persist over extended periods due to diffusive mass exchange.

Conclusions:

• The developed model provides a valuable tool for studying VOC fate and transport in complex subsurface systems.
• The findings highlight the importance of considering interphase mass transfer and back-diffusion in contaminant remediation.
• The model is particularly useful for assessing vapor intrusion risks at sites with contaminated vadose zones and underlying aquifers.