References of "Ground Water"
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See detailPhysically Based Groundwater Vulnerability Assessment Using Sensitivity Analysis Methods
Beaujean, Jean ULg; Lemieux, Jean-Michel; Dassargues, Alain ULg et al

in Ground Water (2013)

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability ... [more ▼]

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability assessment considered here is based on the calculation of sensitivity coefficients for a user-defined groundwater state for which we propose several physically based indicators. Two sensitivity analysis methods are presented: the sensitivity equation method and the adjoint operator method. We show how careful selection of a method can significantly minimize the computational effort. An illustration of the general methodology is presented for the Herten aquifer analog (Germany). This application to a simple, yet insightful, case demonstrates the potential use of this general and physically based vulnerability assessment method to complex aquifers. [less ▲]

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See detailBenzene dynamics and biodegradation in alluvial aquifers affected by river fluctuations
Batlle-Aguilar, Jordi; Morasch, Barbara; Hunkeler, Daniel et al

in Ground Water (2013)

The spatial distribution and temporal dynamics of a benzene plume in an alluvial aquifer strongly affected by river fluctuations was studied. Benzene concentrations, aquifer geochemistry datasets, past ... [more ▼]

The spatial distribution and temporal dynamics of a benzene plume in an alluvial aquifer strongly affected by river fluctuations was studied. Benzene concentrations, aquifer geochemistry datasets, past river morphology and benzene degradation rates estimated in situ using stable carbon isotope enrichment were analysed in concert with aquifer heterogeneity and river fluctuations. Geochemistry data demonstrated that benzene biodegradation was on-going under sulphate reducing conditions. Long-term monitoring of hydraulic heads and characterisation of the alluvial aquifer formed the basis of a detailed modelled image of aquifer heterogeneity. Hydraulic conductivity was found to strongly correlate with benzene degradation, indicating that low hydraulic conductivity areas are capable of sustaining benzene anaerobic biodegradation provided the electron acceptor (SO42-) does not become rate limiting. Modelling results demonstrated that the groundwater flux direction is reversed on annual basis when the river level rises up to two meters, thereby forcing the infiltration of oxygenated surface water into the aquifer. The mobilisation state of metal trace elements such as Zn, Cd and As present in the aquifer predominantly depended on the strong potential gradient within the plume. However, infiltration of oxygenated water was found to trigger a change from strongly reducing to oxic conditions near the river, causing mobilisation of previously immobile metal species and vice versa. Monitored natural attenuation appears to be an appropriate remediation strategy in this type of dynamic environment provided that aquifer characterisation and targeted monitoring of redox conditions is adequate and electron acceptors remain available until concentrations of toxic compounds reduce to acceptable levels. [less ▲]

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See detailInfluence of injection conditions on field tracer experiments
Brouyère, Serge ULg; Carabin, Guy; Dassargues, Alain ULg

in Ground Water (2005), 43(3), 389-400

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of ... [more ▼]

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of injection conditions and well-aquifer interactions, more particularly of the influence of the possible trapping of the tracer in the injection wellbore. Recently, a new mathematical and numerical approach has been developed to model injection conditions and well-aquifer interactions in a very accurate way. Using an analytical solution derived from this model, a detailed analysis is made of the evolution of the tracer input function in the aquifer. By varying injection conditions from one simulation to another, synthetic breakthrough curves are generated with the SUFT3D ground water flow and transport finite-element simulator. These tests show clearly that the shape of the breakthrough curves can be dramatically affected by injection conditions. Using generated breakthrough curves as "actual" field results, a calibration of hydrodispersive parameters is performed, neglecting the influence of injection conditions. This shows that neglecting the influence of actual injection conditions can lead to (1) errors on fitted parameters and (2) misleading identification of the active transport processes. Conclusions and guidelines are drawn in terms of proposed methodologies for better controlling the tracer injection in the field, in order to minimize risk of misinterpretation of results. [less ▲]

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