Estimation of Interstitial Velocity Using a Direct Drive High-Resolution Passive Profiler

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Groundwater velocity is critical for contaminant fate and transport.
• Highly stratified aquifers exhibit significant velocity variations.
• Accurate measurement of groundwater velocity at high resolution is needed.

Purpose of the Study:

• To develop and validate a high-resolution passive profiler (HRPP) for estimating groundwater velocity.
• To use bromide (Br-) mass transfer as a tracer for interstitial velocity.
• To evaluate the HRPP's performance in heterogeneous aquifer conditions.

Main Methods:

• Laboratory experiments using HRPP in flow boxes with varying soil porosities.
• Measuring bromide mass transfer coefficient at different interstitial velocities (0-100 cm/day).
• Employing a 2D quasi-steady-state model to relate velocity and mass transfer.

Main Results:

• A direct, non-linear relationship was found between bromide mass transfer coefficient and velocity.
• The mass transfer coefficient was determined within a single 3-week HRPP deployment.
• Porosity, sampler orientation, and deployment duration had minimal effect on the mass transfer coefficient.

Conclusions:

• The HRPP is a viable tool for estimating groundwater velocity in shallow heterogeneous aquifers.
• The method shows potential for field application with a minimum depth resolution of 10 cm.
• Accurate groundwater velocity data aids in predicting contaminant transport and fate.