Salinity Contributions from Geothermal Waters to the Rio Grande and Shallow Aquifer System in the Transboundary Mesilla (United States)/Conejos-Médanos (Mexico) Basin

Freshwater scarcity has raised concerns about the long-term availability of the water supplies within the transboundary Mesilla (United States)/Conejos-Médanos (Mexico) Basin in Texas, New Mexico, and Chihuahua. Analysis of legacy temperature data and groundwater flux estimates indicates that the region’s known geothermal systems may contribute more than 45,000 tons of dissolved solids per year to the shallow aquifer system, with around 8500 tons of dissolved solids being delivered from localized groundwater upflow zones within those geothermal systems. If this salinity flux is steady and eventually flows into the Rio Grande, it could account for 22% of the typical average annual cumulative Rio Grande salinity that leaves the basin each year—this salinity proportion could be much greater in times of low streamflow. Regional water level mapping indicates upwelling brackish waters flow towards the Rio Grande and the southern part of the Mesilla portion of the basin with some water intercepted by wells in Las Cruces and northern Chihuahua. Upwelling waters ascend from depths greater than 1 km with focused flow along fault zones, uplifted bedrock, and/or fractured igneous intrusions. Overall, this work demonstrates the utility of using heat as a groundwater tracer to identify salinity sources and further informs stakeholders on the presence of several brackish upflow zones that could notably degrade the quality of international water supplies in this developed drought-stricken region.

Hydrogeological effects of dredging navigable canals through lagoon shallows. A case study in Venice

For the first time a comprehensive investigation has been carried out to quantify the possible effects of dredging a navigable canal on the hydrogeological system underlying a coastal lagoon. The study is focused on the Venice Lagoon, Italy, where the port authority is planning to open a new 10 m deep and 3 km long canal to connect the city passenger terminal to the central lagoon inlet, thus avoiding the passage of large cruise ships through the historic center of Venice. A modeling study has been developed to evaluate the short (minutes), medium (months), and long (decades) term processes of water and pollutant exchange between the shallow aquifer system and the lagoon, possibly enhanced by the canal excavation, and ship wakes. An in-depth characterization of the lagoon subsurface along the channel has supported the numerical modeling. Piezometer and sea level records, geophysical acquisitions, laboratory analyses of groundwater and sediment samples (chemical analyses and ecotoxicity testing), and the outcome of 3-D hydrodynamic and computational fluid dynamic (CFD) models have been used to set up and calibrate the subsurface multi-model approach. The numerical outcomes allow us to quantify the groundwater volume and estimate the mass of anthropogenic contaminants (As, Cd, Cu, Cr, Hg, Pb, Se) likely leaked from the nearby industrial area over the past decades, and released into the lagoon from the canal bed by the action of depression waves generated by ships. Moreover, the model outcomes help to understand the effect of the hydrogeological layering on the propagation of the tidal fluctuation and salt concentration into the shallow brackish aquifers underlying the lagoon bottom.

GEOCHEMICAL CHARACTERISTICS OF THE GEOTHERMAL FLUIDS IN THE AKROPOTAMOS AREA (MACEDONIA, NORTHERN GREECE)

The geothermal field of Akropotamos produces fluids at temperatures up to 90oC. The waters from wells AKR-1, AKR-3, AKR-4, AKR-5 and AKR-6 at 30 86oC and TDS of 3.1-30.7 g/l are classified as Na-Cl type. The water from well AKR-2 at 46oC with TDS of 2.15 g/l belongs to Na-HCO3Cl type. The cold and sub-thermal waters (16.4- 27oC) in the area are considered as fresh or low salinity waters (TDS: 0.31-4.34 g/l) of various mixed types. The Na-Cl geothermal waters can be divided into two categories due to two different hot aquifers: (a) Τhe first shallow aquifer contains high salinity waters (TDS: 27.4 30.7 g/l) at 30-48oC located within sands, sandstones and gravels. (b) Τhe second deeper reservoir composed of calcareous conglomerates and sandstones contains lower salinity waters (TDS: 3.1-5.08 g/l) at 83-90οC. The contribution of seawater to the chemical composition of the thermal waters in the shallow aquifer system seems to be important. With the aid of chemical geothermomometers applied to the geothermal water from well AKR-1, the deep temperature has been estimated to be >120oC. Significant quantities of CO2 are encountered in wells AKR-1 and AKR-3.

Hydrogeological effects of dredging navigable canals through lagoon shallows. A case study in Venice

For the first time a comprehensive investigation has been carried out to quantify the possible effects of dredging a navigable canal on the hydrogeological system underlying a coastal lagoon. The study is focused on the Venice Lagoon, Italy, where the Port Authority is planning to open, a new 10-m deep and 3-km long canal to connect the city passenger terminal to the central lagoon inlet thus avoiding the passage of large cruise ships through the historic centre of Venice. A modelling study has been developed to evaluate the short (minutes), medium (months), and long (decades) term processes of water and pollutant exchange between the shallow aquifer system and the lagoon, possibly enhanced by the canal excavation, and ship-wakes. An in-depth characterization of the lagoon subsurface along the channel has supported the numerical modelling. Piezometer and sea level records, geophysical acquisitions, laboratory analyses on groundwater and sediment samples (chemical analyses and ecotoxicity testing), and the outcome of 3D hydrodynamic and computational fluid dynamic (CFD) models have been used to set-up and calibrate the subsurface multi-model approach. The numerical outcomes allow to quantify the groundwater volume and estimate the mass of anthropogenic contaminants (As, Cd, Cu, Cr, Hg, Pb, Se) likely leaked from the nearby industrial area over the past decades, and released into the lagoon from the canal bed by the action of depression waves generated by ships. Moreover, the model outcomes help to understand the effect of the hydrogeological layering on the propagation of the tidal fluctuation and salt concentration into the shallow brackish aquifers underlying the lagoon bottom.