A parametric transfer function methodology for analyzing reactive transport in nonuniform flow

Area of Science:

• Environmental Science
• Geochemistry
• Hydrogeology

Background:

• In-situ bioremediation is a key groundwater cleanup strategy.
• Nonuniform flow fields in multiple-well systems complicate reactive transport analysis.
• Accurate modeling of contaminant and tracer transport is crucial for effective remediation.

Purpose of the Study:

• To develop and validate a transfer function method for analyzing reactive transport in nonuniform flow fields.
• To estimate the first-order degradation rate of ethanol during in-situ bioremediation.
• To compare methods for quantifying tracer loss in complex well systems.

Main Methods:

• Utilized transfer functions with gamma distributions as parametric models.
• Applied temporal moment matching to estimate apparent parameters of classical transport models.
• Jointly analyzed breakthrough curves (BTCs) of bromide (tracer) and ethanol (contaminant).
• Compared scaling factor and first-order decay for tracer loss quantification.

Main Results:

• Gamma and inverse-Gaussian distributions effectively approximated transfer functions when a scaling factor was included.
• Accurate estimation of first-order ethanol degradation rates was achieved for both multi-level sampling (MLS) and extraction wells.
• A first-order decay term for tracer loss inadequately described BTCs at extraction wells due to flow path variations.

Conclusions:

• The transfer function method with gamma distributions and a scaling factor is suitable for reactive transport analysis in complex bioremediation systems.
• This approach enables reliable estimation of degradation rates even in nonuniform flow fields.
• Understanding tracer loss mechanisms is critical for accurate modeling, especially in extraction wells affected by diverse travel paths.