Detecting Seasonal Flow Pathways in Road Structures Using Tracer Tests and ERT

Area of Science:

• Environmental Science
• Hydrogeology
• Geophysics

Background:

• Roads and traffic contribute water-bound pollutants to groundwater.
• Deicing salt application in cold climates poses a risk to groundwater quality.
• Understanding pollutant transport is crucial for groundwater protection and road maintenance.

Purpose of the Study:

• To develop and evaluate a tracer-electrical resistivity tomography (ERT) method for investigating deicing salt infiltration pathways.
• To demonstrate the seasonal variability of pollutant transport in road structures.
• To identify infiltration routes for water-bound road pollutants.

Main Methods:

• Utilized a tracer-ERT monitoring method with dissolved sodium chloride as a tracer.
• Employed a multi-electrode array system to monitor tracer infiltration.
• Conducted year-long tracer tests at the same location across different seasons and weather conditions.

Main Results:

• Observed significant seasonal variations in percolation patterns and flow velocities.
• Documented substantial decreases in infiltration during winter (December).
• Identified preferential flow paths within the road shoulder as a likely cause for reduced winter infiltration.

Conclusions:

• The developed tracer-ERT method is effective for identifying deicing salt infiltration pathways.
• Seasonal factors, particularly frozen conditions, greatly influence pollutant transport dynamics.
• Findings are applicable to understanding the movement of other water-soluble road pollutants to groundwater.