The effects of long-term saline groundwater pumping for desalination on the fresh-saline water interface: Field observations and numerical modeling

Sci Total Environ. 2020 Aug 25;732:139249. doi: 10.1016/j.scitotenv.2020.139249. Epub 2020 May 11.

Abstract

This study tests for the first time the long-term effects of pumping saline groundwater (SGW) as feed for a desalination plant on a coastal aquifer. Field measurements combined with 3D modeling of the hydrological conditions were conducted to examine the effects of SGW pumping on the aquifer system. The plant is next to the city of Almeria (South East Spain) and has been operating since 2006. It uses multiple beach wells along the shore to draw SGW from beneath the fresh-saline water interface (FSI) of the Andarax coastal aquifer. The long-term impact of the intensive pumping on the aquifer was assessed by electrical conductivity profiles in three observation wells during 12 years of pumping. The FSI deepened with continuous pumping, reaching a decrease of ~50 m in the observation well closest to the pumping wells. A calibrated three-dimensional numerical model of the Andarax aquifer replicates the freshening of the aquifer due to the continuous pumping, resulting in a salinity decrease of ~16% in the vicinity of the wells. The salinity decrease stabilizes at 17%, and the model predicts no further significant decrease in salinity for additional 20 years. Submarine groundwater discharge is lowered due to the SGW pumping and ~19,000,000 m3 of freshwater has not lost to the sea during the 12 years of pumping with a rate of ~1,100,000 m3 yr-1 after 6 years of pumping. After pumping cessation, hydrostatic equilibrium would take about 20 years to recover. This work presents the complex dynamics of the FSI due to the SGW pumping for desalination in the first real long-term scenario. It shows by combining field work and numerical modeling, a significant freshening of the aquifer by pumping SGW, emphasizing an additional advantage and the effectiveness of this use as a negative hydraulic barrier against seawater intrusion.

Keywords: Coastal aquifer management; Desalination; Saline groundwater; Seawater intrusion.