Characterization of a managed aquifer recharge system using multiple tracers

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 (δH and δO) 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, N, and O) 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.

Pathline Density Distributions in a Null‐Space Monte Carlo Approach to Assess Groundwater Pathways

“…In fact, mixing between young artificially‐infiltrated water and regional groundwater has been observed in these central locations (Moeck et al ). The fact that only a few realizations resulted in particle tracks that support the field observations highlights the need for a rigorous uncertainty assessment.…”

“…Only the central part of the pumping well gallery might be extracting regional groundwater. Although the simulations show that the probability would be low, mixing between young artificially‐infiltrated water and regional groundwater has been observed in these central locations (Moeck et al ). The need for an uncertainty assessment is highlighted by the fact that only a few realizations resulted in particle tracks that supported the field observations (i.e., mixing between young artificially‐infiltrated water and regional groundwater flowing towards the pumping wells).…”

Integrating Bayesian Groundwater Mixing Modeling With On‐Site Helium Analysis to Identify Unknown Water Sources

“…Figure also shows potential mixing pathways between the artificially infiltrated water (i.e., Rhine water, E 1 ), unknown end‐members ( E res ) and regional groundwater ( E 2 ), which is known to contain certain contaminants (Moeck et al, ). Traces of these contaminants can be found in the abstracted drinking water (Moeck et al, ).…”

Institutional Feasibility of Managed Aquifer Recharge in Northeast Ghana

“…Dillon [23] argues that MAR can harvest and reuse water, citing the City of Mount Gambier in Australia where drainage wells have replenished a karstic aquifer for 120 years without indications of poor water quality. MAR also offers an opportunity to build groundwater mounds which block the inflow of contaminated water from areas upstream [24]. Bouwer [25] explained that artificial recharge can address problems of land subsidence, store water, and enhance water quality through soil aquifer treatment or geo-purification, among many other benefits.…”