『Abstract
Alluvial aquifers are largely used as groundwater resource since
large flow rates can be obtained due to infiltration from the
neighboring river. Reductive conditions in the infiltration flow
path, caused by the degradation of organic matter, can induce
effects detrimental to water quality, such as dissolution of Mn
and Fe from the aquifer sediments. In the absence of any direct
relationship between the redox potential (Eh) and reductive conditions
favorable to manganese and/or iron reduction, we propose a quantitative
approach, the electron trapping capacity (ETC). It is calculated
using dissolved O2 and NO3
concentrations in groundwater, weighted for the quantity of electrons
these two species can trap during the oxidation of organic matter.
This approach, tested on several field and laboratory investigations,
indicates that reductive dissolution of manganese and iron oxyhydroxides
occurs for an ETC lower than 0.2 mmol L-1. exceptions
to that threshold value are observed when Mn-rich groundwater
flows too fast out of a reduced zone into an oxidizing environment
to permit equilibrium precipitation of Mn oxyhydroxides.
Keywords: Alluvial aquifer; Riverbank filtration; Redox reactions;
Organic matter; Reduced zone』
Introduction
The sites investigated
Characterizing redox conditions
Validation of the approach
Redox potential (Eh) as indicator of conditions favorable
for the reduction of Mn
ETC: A better indicator for characterizing conditions favorable
to the reductive dissolution of manganese oxides?
ETC and iron reductive dissolution
Conclusion
Acknowledgements
References