Characterization of a managed aquifer recharge system using multiple tracers

Christian Moeck; Dirk Radny; Andrea Popp; Matthias Brennwald; Sebastian Stoll; Adrian Auckenthaler; Michael Berg; Mario Schirmer

doi:10.1016/j.scitotenv.2017.07.211

Characterization of a managed aquifer recharge system using multiple tracers

Sci Total Environ. 2017 Dec 31:609:701-714. doi: 10.1016/j.scitotenv.2017.07.211. Epub 2017 Jul 28.

Authors

Christian Moeck¹, Dirk Radny², Andrea Popp³, Matthias Brennwald², Sebastian Stoll², Adrian Auckenthaler⁴, Michael Berg², Mario Schirmer⁵

Affiliations

¹ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland. Electronic address: Christian.moeck@eawag.ch.
² Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
³ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland; Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland.
⁴ Office of Environmental Protection and Energy, Canton Basel-Country, Switzerland.
⁵ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland; Centre of Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Neuchâtel, Switzerland.

PMID: 28763667
DOI: 10.1016/j.scitotenv.2017.07.211

Abstract

Knowledge about the residence times of artificially infiltrated water into an aquifer and the resulting flow paths is essential to developing groundwater-management schemes. To obtain this knowledge, a variety of tracers can be used to study residence times and gain information about subsurface processes. Although a variety of tracers exists, their interpretation can differ considerably due to subsurface heterogeneity, underlying assumptions, and sampling and analysis limitations. The current study systematically assesses information gained from seven different tracers during a pumping experiment at a site where drinking water is extracted from an aquifer close to contaminated areas and where groundwater is artificially recharged by infiltrating surface water. We demonstrate that the groundwater residence times estimated using dye and heat tracers are comparable when the thermal retardation for the heat tracer is considered. Furthermore, major ions, acesulfame, and stable isotopes (δ²H and δ¹⁸O) show that mixing of infiltrated water and groundwater coming from the regional flow path occurred and a vertical stratification of the flow system exist. Based on the concentration patterns of dissolved gases (He, Ar, Kr, N₂, and O₂) and chlorinated solvents (e.g., tetrachloroethene), three temporal phases are observed in the ratio between infiltrated water and regional groundwater during the pumping experiment. Variability in this ratio is significantly related to changes in the pumping and infiltration rates. During constant pumping rates, more infiltrated water was extracted, which led to a higher dilution of the regional groundwater. An infiltration interruption caused however, the ratio to change and more regional groundwater is extracted, which led to an increase in all concentrations. The obtained results are discussed for each tracer considered and its strengths and limitations are illustrated. Overall, it is demonstrated that aquifer heterogeneity and various subsurface processes necessitate application of multiple tracers to quantify uncertainty when identifying flow processes.

Keywords: Acesulfame; Groundwater residence time; Managed aquifer recharge; Noble gases; Time series; Urban hydrogeology.