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- PublicationMétadonnées seulementNatural tracers to quantify seasonal variations of groundwater mixing in a complex alluvial aquifer (Pfynwald, Switzerland)(: Int Assoc Hydrological Sciences, 2000)
;Schurch, Marc ;Dassargues, AlainDissolved sulphate, oxygen-18, deuterium and tritium have been used to quantify seasonal variations of groundwater mixing in a complex alluvial aquifer in the upper Rhone valley (Pfynwald, Wallis, Switzerland). The concentration of these four natural tracers reflects spatial and seasonal chemical variations of the alluvial Rhone aquifer. Further they represent mixing rates between weakly mineralized infiltrated Rhone River water and SO4-rich water flowing from the south valley side. The delta O-18 composition decreases from -14.03 parts per thousand at the south valley side to -14.85 parts per thousand near the Rhone River and follows the general groundwater flow pattern as well as the observed dissolved sulphate distribution. A positive correlation exists between the delta O-18 values and sulphate concentrations and can be represented by a linear regression. A two-component model has been applied to tritium concentrations to calculate groundwater mixing rates during high and low water-level periods.
- PublicationMétadonnées seulement
- PublicationMétadonnées seulementGeochemical indicators to determine relations between spring behaviour and water losses of a divergence tunnel(2001)
;Schurch, MarcHydraulic and geochemical relations between a subthermal, SO4-rich spring (Q6) and water losses of a divergence tunnel indicate that both features are hydraulically connected. The divergence tunnel, crossing the evaporite rocks of the Penninic Pontis-Nappe (anhydrite, gypsum, dolomitic limestones) in the Rhone River valley (Central Wallis, Switzerland), deviates water from the Rhone River at a rate of up to 62 m(3)/s. The recharge rate of weakly mineralized water exfiltrating from the divergence tunnel and flowing to the Q6 spring varied between 0.5 and 5 l/s, depending on seasonal variations of the discharge in the divergence tunnel. Methods used to determine the degree of connection included discharge measurements, continuous and monthly water quality measurements, and geochemical modelling. Hydrochemical indicators of particular significance include major inorganic ions, as well as temperature, pH, calcite and gypsum saturation indices. Following the divergence tunnel decommissioning in August 17 1998, simultaneous rises in spring temperature from 13.0 to 13.7 degreesC and electrical conductivity from 2430 to 2600 muS/cm were recorded. A decline in spring discharge from 10 to 6.7 l/s was also observed.
- PublicationMétadonnées seulement
- PublicationMétadonnées seulementHydraulic parameters in a porous aquifer: hydrogeological & geophysical logging methods(2001)
;Schurch, Marc ;Monnet, R ;Chapellier, D
- PublicationMétadonnées seulementBiocolloid and solute tracer transport in gravel aquifers - a groundwater protection perspectiveMigration conditions in a gravel aquifer of the upper Rhone River valley were studied using particle and solutes as contaminant surrogates. Transport rates were 130 to 480 m/d over distances to 22 in, up to 40 times faster than predicted using conventional flow/effective porosity parameters. In one well, a 1-m vertical pathway heterogeneity dominated the 12-m aquifer saturated thickness. Biocolloids were consistently detected earlier than solutes due in part to their significantly lower detection limits and possibly to preferential particle advection. Biocolloid detection occurred 3- to 7-times earlier than time to solute breakthrough peaks, those values commonly relied on when calculating reference velocity parameters. Relative colloid recovery was typically 1.5 to 4 percent and in one case was 72 % of the solute illustrating relatively low biocolloid attenuation in river gravel macropores. Transport direction was up to 90 degrees off those determined from head-derived measurements. Results suggest that reliable groundwater protection strategy in heterogeneous gravel aquifers may improve when field-verified with migration characterization using multiple tracer types.