Re-Purposing Groundwater Flow Models for Age Assessments: Important Characteristics

Area of Science:

• Hydrogeology
• Environmental Modeling
• Water Resource Management

Background:

• Groundwater flow model construction is resource-intensive.
• Re-purposing existing models for new applications like age and transport simulations is increasingly relevant.
• Limited guidance exists on model characteristics crucial for re-purposing for age and transport studies.

Purpose of the Study:

• To evaluate the impact of groundwater flow model complexity on simulated groundwater age metrics.
• To compare age metrics across different watershed scales (HUC 8 to HUC 12).
• To identify key model characteristics for successful re-purposing for age and transport simulations.

Main Methods:

• Developed three MODFLOW-MODPATH models of varying complexity (layering, heterogeneity) for the same area.
• Compared simulated groundwater age metrics (young fraction, median age of young/old fractions).
• Evaluated model performance across three watershed scales.

Main Results:

• The young fraction is less sensitive to model layering than median age metrics, suggesting simpler models suffice for basic susceptibility assessments.
• Water table mounding and discharge into partially penetrating streams significantly impact young fraction and median age simulations.
• The influence of head-water streams on age simulations is consistent across different porosity distributions.

Conclusions:

• Modelers can re-purpose existing groundwater flow models for age simulations, with simpler models adequate for basic susceptibility assessments.
• Incorporating stream-aquifer interactions is vital for accurate groundwater age and transport modeling.
• This study provides insights for evaluating the suitability of existing models for age-related simulations.