Enhanced pumping test using physicochemical tracers to determine surface-water/groundwater interactions in an alluvial island aquifer,river Rhône,France     

Poulain  Angélique  Marc  Vincent  Gillon  Marina  Mayer  Adriano  Cognard-Plancq  Anne-Laure  Simler  Roland  Babic  Milanka  Leblanc  Marc 《Hydrogeology Journal》2021,29(4):1569-1585

Groundwater extracted from the Barthelasse Island aquifer, surrounded by the river Rhône (southeastern France), contributes to the drinking water supplies of 180,000 inhabitants. Owing to its location close to the river and the presence of two backwaters (oxbow lakes), the pumped groundwater is highly vulnerable to river pollution. A pumping test was conducted over 24 h to analyse and quantify the water exchange processes between the river, backwaters and groundwater. During the pumping test, isotopic (δ¹⁸O, δ²H and ²²²Rn), hydrochemical and hydrophysical monitoring of the groundwater was undertaken. Hydraulic heads were measured in pumping wells and at a piezometer located between the wells. Discrete water samples were collected at several observation points in the field, including the backwater and river. The results show mixing between three end-members, as defined by the deuterium excess and silica concentration, led by river Rhône water which had been affected by water–rock interactions over time and mixing with surface evaporated waters. The pumped water resulted from mixing between three end-members, all of which depended on the river Rhône but differed in terms of residence time in the system. Although the groundwater pumping wells are close to each other (<70 m) and have similar depths, the changes in the contributions from end-member waters at each well were different during the pumping test. Comparing isotopic tracers and geochemistry made it possible to quantify the different hydrological compartments that contribute to the groundwater pumped from the boreholes, which is critical in constructing a conceptual flow model.

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Estimate of recharge of a rising water table in semiarid Niger from 3H and 14C modeling   总被引：1，自引：0，他引：1  

Favreau G  Leduc C  Marlin C  Dray M  Taupin JD  Massault M  Le G  Babic M 《Ground water》2002,40(2):144-151

A hydrodynamic survey carried out in semiarid southwest Niger revealed an increase in the unconfined ground water reserves of approximately 10% over the last 50 years due to the clearing of native vegetation. Isotopic samplings (3H, 18O, 2H for water and 14C, 13C for the dissolved inorganic carbon) were performed on about 3500 km2 of this silty aquifer to characterize recharge. Stable isotope analyses confirmed the indirect recharge process that had already been shown by hydrodynamic surveys and suggested the tracers are exclusively of atmospheric origin. An analytical model that takes into account the long-term rise in the water table was used to interpret 3H and 14C contents in ground water. The natural, preclearing median annual renewal rate (i.e., recharge as a fraction of the saturated aquifer volume) lies between 0.04% and 0.06%. For representative characteristics of the aquifer (30 m of saturated thickness, porosity between 10% and 25%), this implies a recharge of between 1 and 5 mm/year, which is much lower than the estimates of 20 to 50 mm/year for recent years, obtained using hydrological and hydrodynamic methods and the same aquifer parameters. Our study, therefore, reveals that land clearing in semiarid Niger increased ground water recharge by about one order of magnitude.  相似文献