Solute transport under non-linear sorption and decay.

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Contaminant transport in aquifers is typically modeled using the advective-dispersive equation.
• Non-linear processes like degradation, decay, or sorption complicate standard modeling approaches.
• Accurate prediction of contaminant plume behavior under these non-linear conditions is crucial for risk assessment.

Purpose of the Study:

• To develop and validate novel simulant solutions for non-linear contaminant transport.
• To analyze contaminant plume behavior under non-linear decay and sorption (Freundlich and Langmuir isotherms).
• To provide accurate forecasting tools for contaminant propagation in laboratory and field settings.

Main Methods:

• Employed the method of decomposition to derive series solutions for non-linear advective-dispersive equations.
• Developed closed-form 'simulant' solutions approximating segments of the derived series.
• Tested solutions against instantaneous spill and constant concentration boundary conditions, validating with existing linear and finite difference solutions.

Main Results:

• Simulant solutions demonstrated simplicity, stability, and flexibility for forecasting non-linear contaminant transport.
• Non-linear decay resulted in plume profile re-scaling, dependent on non-linear parameters 'b' and 'C'.
• Non-linear Freundlich sorption significantly retarded contaminant transport, with plume shape sensitivity to parameters 'b' and 'C'; Langmuir isotherm showed sensitivity to 'alpha'.

Conclusions:

• The derived simulant solutions provide accurate approximations for non-linear contaminant transport phenomena.
• These models quantitatively capture non-linear retardation effects and plume shape sensitivities, crucial for site investigations.
• The findings offer practical tools for predicting contaminant plume evolution under complex, real-world conditions.