Modeling a well-characterized perfluorooctane sulfonate (PFOS) source and plume using the REMChlor-MD model to...

Area of Science:

• Environmental Science
• Hydrogeology
• Environmental Chemistry

Background:

• Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants.
• Sorption and matrix diffusion are key retention processes for PFAS in groundwater.
• Understanding these processes is critical for effective environmental remediation and risk assessment.

Purpose of the Study:

• To model the concentration and mass discharge of perfluorooctane sulfonate (PFOS) in groundwater.
• To incorporate matrix diffusion processes into the REMChlor-MD model for PFOS transport.
• To assess the impact of matrix diffusion on PFOS plume behavior and persistence.

Main Methods:

• Utilized data from a chemically and geologically characterized site.
• Employed the REMChlor-MD model, incorporating matrix diffusion.
• Compared model predictions with field data for concentration, mass discharge, and total mass.

Main Results:

• The REMChlor-MD model with matrix diffusion accurately reproduced field data for PFOS concentration, mass discharge, and total mass.
• A model without matrix diffusion showed a significantly poorer match to field data.
• After 40 years, 80% of PFOS mass exiting source zones was found in downgradient low-permeability zones due to matrix diffusion.
• PFOS plume expansion is forecasted to be limited, slowing from 350m in 2017 to 550m in 2070.

Conclusions:

• Matrix diffusion is a highly relevant process influencing PFOS persistence in the environment.
• Matrix diffusion significantly slows the expansion rate of groundwater plumes for non-degrading contaminants like PFOS.
• The findings have important implications for monitored natural attenuation strategies for PFAS contamination.