Evaluating backward probability model under various hydrogeologic and hydrologic conditions.

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Contaminant source identification is crucial for effective remediation and water resource management.
• The backward probability model estimates contaminant source locations and release times.
• Rigorous verification of the backward probability model is essential for reliable application.

Purpose of the Study:

• To present a model verification framework for the backward probability model.
• To evaluate the model's reliability under various hydrogeologic conditions, from simple to complex.
• To assess the model's performance in transient saturated and variably-saturated flow.

Main Methods:

• A stepwise verification approach was employed, starting with simple 1D homogeneous problems.
• Model verification involved comparisons with previous studies under steady-state and transient flow.
• Complex heterogeneous conditions were assessed by comparing forward and backward probability simulations.

Main Results:

• The backward probability model demonstrated good performance for homogeneous problems.
• For heterogeneous problems, slight differences in backward travel times were observed due to solute decay and boundary conditions.
• Despite minor travel time variations, the backward travel time at maximum probability was well reproduced in heterogeneous scenarios.

Conclusions:

• The backward probability model is a reliable tool for contaminant source identification, particularly in homogeneous settings.
• The model's ability to reproduce maximum probability travel times suggests its utility in complex hydrogeologic environments.
• The presented verification framework supports the robust application of the backward probability model in environmental assessments.