Line-source multi-tracer test for assessing high groundwater velocity

Area of Science:

• Hydrogeology
• Environmental Science
• Geophysics

Background:

• Point-source tracer tests often fail to provide reliable groundwater flow data in high-flux environments.
• Traditional methods require modification to accurately assess subsurface hydrological properties.
• Aquifer heterogeneity can significantly impact tracer test outcomes.

Purpose of the Study:

• To evaluate the effectiveness of segmented line-source multi-tracer injection for assessing groundwater velocities and flow directions.
• To address limitations of point-source tracer tests in complex subsurface conditions.
• To investigate the potential of line-source injection for characterizing aquifer heterogeneity.

Main Methods:

• A field experiment utilized an 8-m segmented line injection system with four distinct tracers (uranine, Na naphthionate, Rhenium oxide, Gd-DTPA).
• Tracers were injected perpendicular to the assumed groundwater flow direction in the Dead Sea coast region.
• Tracer transport was monitored in an array of five downstream boreholes within a 10x10 m area.

Main Results:

• Tracers were detected within 0.7 to 2.3 hours in four of five observation wells, located 2.3 to 10 m from the injection system.
• Groundwater velocities were estimated to be approximately 80 to 170 m/d based on tracer recovery.
• Groundwater flow direction correlated well with the observed hydraulic gradient.

Conclusions:

• Segmented line-source multi-tracer injection is a viable and effective technique for determining groundwater velocity and flow direction.
• This method offers improved reliability over point-source tests, especially in subsurfaces with high water flux.
• The approach provides valuable insights into local groundwater dynamics and aquifer characteristics.