Hydrogeochemical processes in the vicinity of a desalination plant (Cabo de Gata, SE Spain)

Abstract

This study provides geochemical data with the aim of assisting in the proper managing of groundwater resources and so avoiding negative impacts on the aquifers. The area covers the coastal aquifer of Cabo de Gata, which supplies a new desalination plant. Groundwater samples, to different depths, were characterized to identify the main processes occurring in the system, as well as to establish their relationship with seawater. Major and minor elements, and their ionic ratios distinguish two groups of samples: G1) samples containing between 7 and 70% seawater, with SO 4 2−/Cl − and Br/Cl − ratios that decrease with salinity; G2) water containing between 99 and 112% of seawater, SO 4 2−/Cl − similar to that of seawater (0.12) and a Br/Cl − ratio that increases with salinity. Different scenarios were simulated using PHREEQC geochemical code: a) conservative seawater–freshwater mixing, b) modified freshwater–seawater mixing, c) freshwater-modified seawater mixing and d) modified freshwater–modified seawater mixing. Modeling results indicate that the processes that best match the groundwater samples are different for the two groups identified. Water in group 1 is best simulated by a mix of modified freshwater (by water–rock interaction processes) with seawater, and group 2 by mixing a modified (evaporated) seawater with freshwater.