3-D numerical evaluation of density effects on tracer tests

Area of Science:

• Hydrogeology
• Environmental Engineering
• Geophysics

Background:

• Tracer tests are crucial for understanding groundwater flow.
• Density variations in injected tracers can influence plume behavior.
• Field conditions often involve natural hydraulic gradients.

Purpose of the Study:

• To assess the significance of density-dependent flow on tracer plume development.
• To identify key parameters influencing density effects in tracer tests.
• To understand the interplay between tracer mass, aquifer properties, and density flow.

Main Methods:

• Numerical simulations using a three-dimensional model.
• Analysis of tracer plume development under varying parameters.
• Interpretation via concentration contours and first moment analysis.
• Modeling different hydraulic conductivity fields.

Main Results:

• Tracer injections below 0.036 kg/m do not cause significant density effects with hydraulic gradients ≥0.1%.
• Higher tracer masses or shallow aquifers can induce early-phase buoyancy-induced flow, affecting plume development.
• Tracer injection rates and durations have a negligible impact on density flow.
• Local hydraulic conductivity variations control tracer distribution but do not mask buoyancy effects.

Conclusions:

• Density effects are important for high tracer masses and in shallow aquifers.
• Moderate hydraulic gradients can minimize density-driven flow issues in typical tracer tests.
• Buoyancy-induced flow is a critical factor in early tracer plume development, independent of injection scenario details.