Estimating reaction rate coefficients within a travel-time modeling framework.

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Groundwater remediation in heterogeneous aquifers presents challenges due to complex subsurface flow and transport.
• Accurate estimation of in situ reaction rate coefficients is crucial for effective contaminant degradation and remediation design.

Purpose of the Study:

• To develop a generalized, efficient, and practical approach for estimating in situ reaction rate coefficients in heterogeneous aquifers.
• To utilize a travel-time modeling framework combined with tracer test data for improved reaction rate estimation.

Main Methods:

• Employing a travel-time modeling framework using conservative and reactive tracers in field tracer tests.
• Measuring breakthrough curves (BTCs) to infer travel-time distributions and estimate reaction kinetics.
• Developing simplified schemes for various reaction orders (zero-, first-, nth-, Michaelis-Menten).

Main Results:

• The developed approach effectively estimates in situ reaction rate coefficients without extensive aquifer characterization.
• Validation in a synthetic aquifer and a field-scale bioremediation experiment confirmed the method's practicality and accuracy.
• Field application indicated zero-order kinetics better describe ethanol degradation for U(VI)-bioremediation than first-order kinetics.

Conclusions:

• The travel-time modeling approach offers an efficient and practical alternative to traditional methods for reaction rate estimation in groundwater remediation.
• This method enhances the understanding and modeling of reactive transport in heterogeneous subsurface environments.
• The findings support the optimization of bioremediation strategies by accurately characterizing contaminant degradation kinetics.