Modeling Mechanical Dispersion by Using the Method of Advective Transport Phenomena, a First Step.

Area of Science:

• Hydrogeology
• Environmental Engineering
• Computational Modeling

Background:

• Classical Fickian models describe mechanical dispersion using concentration gradients, which may not fully capture complex groundwater flow dynamics.
• A theoretical advancement is needed for practical implementation in groundwater modeling, addressing limitations of existing approaches.

Purpose of the Study:

• To develop a new theoretical framework for mechanical dispersion in groundwater, accounting for velocity variations.
• To introduce a practical method for implementing advanced dispersion models in numerical simulations.

Main Methods:

• The Advective Transport Phenomena method was employed to model mechanical dispersion based on particle spread at a sub-model scale.
• A new parameter, "dispersive volume shift," was defined, dependent on traveled distance and aquifer heterogeneity (characteristic lengths, log conductivity variance).
• A spreadsheet model simulated longitudinal concentration distribution in homogeneous and heterogeneous aquifers.

Main Results:

• The new model successfully simulated plume behavior, including asymmetry in heterogeneous aquifers, which is not predicted by classical Fickian models.
• The "dispersive volume shift" parameter was shown to be determined by traveled distance and aquifer properties.
• The study highlights the importance of aquifer heterogeneity in mechanical dispersion.

Conclusions:

• The Advective Transport Phenomena method provides a more accurate representation of mechanical dispersion compared to classical Fickian models.
• Further development is required to integrate this approach into general numerical groundwater modeling.
• The findings offer a pathway to improved predictions of contaminant transport in complex aquifer systems.