A mass balance approach to resolving LNAPL stability.

Area of Science:

• Environmental Science
• Geochemistry
• Hydrogeology

Background:

• Light nonaqueous phase liquids (LNAPLs) pose environmental risks.
• Understanding LNAPL behavior is crucial for effective remediation.
• Natural attenuation processes are often overlooked in LNAPL management.

Purpose of the Study:

• To investigate the role of natural LNAPL losses in controlling LNAPL body extent and flux.
• To validate the hypothesis that dissolution and evaporation govern LNAPL dynamics.
• To develop predictive models for field-scale LNAPL behavior.

Main Methods:

• A proof-of-concept sand tank experiment using methyl tert-butyl ether (MTBE) as the LNAPL.
• Stepwise increase of LNAPL injection rates to observe body expansion dynamics.
• Development of analytical solutions for one-dimensional, circular, and oblong LNAPL body geometries.
• Extrapolation of experimental findings to field-scale conditions.

Main Results:

• LNAPL bodies initially expanded rapidly but stabilized over time.
• Stable LNAPL extent was achieved when addition rates equaled loss rates (dissolution and evaporation).
• Analytical solutions described LNAPL fluxes and extent as functions of position and time.
• Natural losses were shown to be critical in governing LNAPL fluxes and extent.

Conclusions:

• Natural losses through dissolution and evaporation are key controlling factors for LNAPL body size and flux.
• The findings support the importance of considering natural attenuation in LNAPL site assessments.
• The developed analytical solutions provide a framework for predicting LNAPL behavior at field scales.