10:45 AM - 12:15 PM
[AHW20-P01] Gases as artificial Tracers to study Surface water - Groundwater Interactions
Keywords:groundwater, gas, mass spectrometer, preferential flowpath, surface water, river infiltration
Groundwater (GW) and surface water (SW) are interconnected, and understanding their interactions is crucial for drinking water management and ecological reasons, particularly in the context of climate change. However, these interactions are complex due to heterogeneous geological properties of the subsurface, leading to preferential groundwater flowpaths.
Tracers are often utilized to study GW-SW interactions, but some traditional tracers such as dyes may be difficult to handle and cause issues with public acceptance. In this regard, gas tracers offer a promising alternative as they are invisible, non-toxic, conservative, and easy to handle. Furthermore, recent advancements in portable mass spectrometer technology allow their direct and continuous measurement in the field (Brennwald 2016, Chatton 2016). Some technical and financial limitations prevent them being used routinely in the study of SW-GW interactions, as their injection into rivers with bubbling methods would require large volumes of gases for long-term experiments in high-discharge environments. These limitations undermine the application of gas tracers in this context.
In this study, we investigated the GW-SW exchange between a pre-alpine river and an alluvial aquifer in the Emme region of Switzerland. We employed cheap and accessible material to develop a cost-effective approach of diffusive injection to efficiently supersaturate the river water with gas. Our injection lasted 35 days, leading to consistent supersaturation of river water one order of magnitude higher than air-saturated water. The dissolved gas concentration was monitored in the river and in a well, as well as in several piezometers, to provide quantitative information on infiltration dynamics. Our results confirmed the hydraulic connection between the infiltrating river and the well and revealed preferential groundwater flowpaths in the alluvial aquifer. A pulse gas tracer test with an injection directly into groundwater confirmed this preferential flow path, with groundwater velocities of 13m per hour.
This long and continuous time series provides ideal input and output functions for physically based numerical models to quantify mixing ratios and transit time distributions.
Tracers are often utilized to study GW-SW interactions, but some traditional tracers such as dyes may be difficult to handle and cause issues with public acceptance. In this regard, gas tracers offer a promising alternative as they are invisible, non-toxic, conservative, and easy to handle. Furthermore, recent advancements in portable mass spectrometer technology allow their direct and continuous measurement in the field (Brennwald 2016, Chatton 2016). Some technical and financial limitations prevent them being used routinely in the study of SW-GW interactions, as their injection into rivers with bubbling methods would require large volumes of gases for long-term experiments in high-discharge environments. These limitations undermine the application of gas tracers in this context.
In this study, we investigated the GW-SW exchange between a pre-alpine river and an alluvial aquifer in the Emme region of Switzerland. We employed cheap and accessible material to develop a cost-effective approach of diffusive injection to efficiently supersaturate the river water with gas. Our injection lasted 35 days, leading to consistent supersaturation of river water one order of magnitude higher than air-saturated water. The dissolved gas concentration was monitored in the river and in a well, as well as in several piezometers, to provide quantitative information on infiltration dynamics. Our results confirmed the hydraulic connection between the infiltrating river and the well and revealed preferential groundwater flowpaths in the alluvial aquifer. A pulse gas tracer test with an injection directly into groundwater confirmed this preferential flow path, with groundwater velocities of 13m per hour.
This long and continuous time series provides ideal input and output functions for physically based numerical models to quantify mixing ratios and transit time distributions.