Investigation of surface water and groundwater interaction (SW–GW interaction) provides basic information for regional water-resource protection, management, and development. In this survey of a 10-km-wide area along both sides of the Songhua River, northeast China, the hydrogeochemical responses to different SW–GW interactions were studied. Three types of SW–GW interactions were identified—“recharge”, “discharge”, and “flow-through”—according to the hydraulic connection between the surface water and groundwater. The single factor index, principal component analysis, and hierarchical cluster analysis of the hydrogeochemistry and pollutant data illuminated the hydrogeochemical response to the various SW–GW interactions. Clear SW–GW interactions along the Songhua River were revealed: (1) upstream in the study area, groundwater usually discharges into the surface water, (2) groundwater is recharged by surface water downstream, and (3) discharge and flow-through coexist in between. Statistical analysis indicated that the degree of hydrogeochemical response in different types of hydraulic connection varied, being clear in recharge and flow-through modes, and less obvious in discharge mode. During the interaction process, dilution, adsorption, redox reactions, nitrification, denitrification, and biodegradation contributed to the pollutant concentration and affected hydrogeochemical response in the hyporheic zone.

Surface-water/groundwater exchange through the evaluation of riparian-zone temperature data has attracted increasing attention in recent years. The Fox Ditch Canal, Nevada, USA, was chosen for this study on seasonal variations of riparian-zone water exchange. Groundwater temperature and hydraulic head real-time monitoring data were collected from March to November 2012. A calibrated hydro-thermal coupling model was used to characterize the riparian-zone temporal and spatial temperature distribution, thereby providing a standard against which the performances of four analytical solution models for calculated riparian-zone vertical seepage velocity could be assessed. The results indicated that the proposed model provided a simulation that was able to represent dynamic changes in riparian-zone soil temperature. Although small variations in patterns and magnitudes of riparian-zone water exchange were evident at a daily scale, they varied significantly over a seasonal scale. Comparison of the results of the four analytical solutions and numerical computation found that the Hatch solution by the amplitude method provided the highest accuracy for calculating groundwater velocity in this area (2.47 × 10⁻⁶ to 3.15 × 10⁻⁶ m/s). Global sensitivity analysis of hydro-thermal coupling model parameters showed that porosity had the most significant impact on temperature in the model.

Health issues related to aquifer contamination with perchlorate are a growing concern in drinking water management. This study describes perchlorate transport and degradation processes from a contaminated stream toward drinking water pumping wells. Investigations are based on laboratory experiments and field measurements conducted at a well field near Bordeaux (France) in a heterogeneous carbonate aquifer interacting with a stream. Field measurements facilitated the characterization of perchlorate contamination and stream-to-aquifer flow. Experiments on columns of streambed sediments conducted in the laboratory confirmed that perchlorate had been degraded in the hyporheic zone. A one-dimensional reactive transport model was implemented to estimate Monod kinetic rates, which account for the inhibition of perchlorate degradation by nitrate. The estimated half-saturation constant for perchlorate [Formula: see text]) is 6.93 10⁻⁹ mol L⁻¹ and the estimated maximum specific degradation rate ([Formula: see text]) ranges between 10⁻⁵ and 4.0 10⁻³ mol L⁻¹ day⁻¹. Despite degradation in the hyporheic zone, perchlorate-contaminated stream water reaches drinking-water-production units. Such contamination highlights the effects of preferential flow paths between the stream and the pumping wells and significant hydraulic gradients caused by drawdowns. In such contexts, in spite of a good potential for degradation, riverbank filtration may not be effective for the protection of drinking water wells. Lessons from this study also reveal that contamination monitoring can be misleading: low concentrations can be reported in monitoring wells between the contaminant source and the production wells, but the latter may yet be contaminated.

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