Field-scale prediction of enhanced DNAPL dissolution based on partitioning tracers

Area of Science:

• Environmental Engineering
• Hydrogeology
• Contaminant Transport

Background:

• Dense nonaqueous phase liquids (DNAPLs) like tetrachloroethylene (PCE) pose significant environmental challenges.
• Accurate modeling of DNAPL dissolution is crucial for effective site remediation.
• The equilibrium streamtube (EST) model offers a promising analytical approach for DNAPL dissolution prediction.

Purpose of the Study:

• To apply the equilibrium streamtube (EST) model to predict DNAPL dissolution at a PCE-contaminated dry cleaner site.
• To evaluate the EST model's performance using field-measured data and simulated data from a multiphase flow model.
• To investigate the influence of well configuration and flow patterns on DNAPL dissolution predictions.

Main Methods:

• Utilized the equilibrium streamtube (EST) model, an analytical solution requiring field-measurable parameters.
• Parameterized the EST model using data from a field-scale partitioning tracer test.
• Compared EST predictions with field data from an in-situ ethanol flood and simulated data from the UTCHEM model.
• Assessed DNAPL dissolution under both forced-gradient and natural gradient flow conditions.

Main Results:

• The EST model accurately predicted ethanol recovery, achieving high Nash-Sutcliffe efficiency (E=0.96 with field data, E=0.90 with simulated data).
• EST predictions for PCE dissolution showed earlier arrival times compared to field data, attributed to differences in well screen intervals.
• Under natural gradient conditions, EST underestimated total PCE mass removal compared to UTCHEM simulations, suggesting tracer detection limitations in stagnant zones.

Conclusions:

• The EST model is a valuable tool for predicting DNAPL dissolution, particularly for compounds like ethanol.
• Well screen configuration and resulting flow patterns significantly impact the accuracy of DNAPL dissolution predictions.
• Tracer tests may not fully capture contaminant mass in complex flow fields with stagnation zones, highlighting the need for careful experimental design.