Hydrogeochemical modelling of water-sediment interactions during infiltration of monovalent-partial desalinated water into different dune sediments

The salinization of groundwater due to saltwater intrusion in coastal regions requires efficient mitigation strategies, e.g., the infiltration of desalinated water via Managed Aquifer Recharge, such as ponded infiltration or injection wells, to ensure the supply of drinking water. It has been shown that the infiltration of desalinated water into an aquifer may result in a series of deteriorating chemical reactions. To counteract this problem, the goal of the cooperative project “innovatION” is to develop a new desalination membrane, which aims to reduce mainly monovalent ions only to achieve a more sustainable and efficient desalination technology.

To give an outlook on possible water-sediment interactions during the infiltration of monovalent desalinated water into aquifers, column experiments were realised using different dune sediments from the Island of Langeoog, North-West Germany. The experimental data suggest cation exchange and calcite dissolution as the main processes occurring (compare abstract Braeunig et al.). For a process-based quantitative description and analysis of all relevant processes and their interactions, PHREEQC models were created for the individual experiments. The models support the experimental data and the hypothesized reaction network, and even allowed for the identification of  reactions (e.g. cation exchange and calcite dissolution), as well as their impact on the overall system behaviour.