Characterization of a managed aquifer recharge system using multiple tracers.

Area of Science:

• Hydrogeology
• Environmental Science
• Geochemistry

Background:

• Understanding groundwater residence times and flow paths is vital for effective groundwater management, especially in areas with artificial recharge and potential contamination.
• Various tracers can provide insights into subsurface processes, but their interpretation is complex due to heterogeneity and limitations.

Purpose of the Study:

• To systematically assess the information gained from seven different tracers during a pumping experiment at a drinking water extraction site with artificial groundwater recharge.
• To compare the effectiveness and limitations of different tracers in characterizing groundwater flow and residence times.

Main Methods:

• Conducted a pumping experiment involving artificial infiltration of surface water into an aquifer.
• Utilized seven different tracers: dye, heat, major ions, acesulfame, stable isotopes (δ²H, δ¹⁸O), dissolved gases (He, Ar, Kr, N₂, O₂), and chlorinated solvents.
• Analyzed tracer concentration patterns and residence times in relation to pumping and infiltration rates.

Main Results:

• Groundwater residence times estimated using dye and heat tracers were comparable when thermal retardation was considered.
• Major ions, acesulfame, and stable isotopes indicated mixing of infiltrated and regional groundwater, with vertical stratification observed.
• Dissolved gases and chlorinated solvents revealed three temporal phases in the infiltrated water to regional groundwater ratio, influenced by pumping and infiltration rates.

Conclusions:

• Aquifer heterogeneity and complex subsurface processes necessitate the use of multiple tracers to accurately quantify uncertainty in flow process identification.
• The study highlights the strengths and limitations of each tracer, providing a comprehensive understanding for groundwater management strategies.