Saline groundwater extraction as a measure to increase the freshwater availability A case study for the western parts of the Netherlands

Abstract

Autonomous salinization threatens freshwater availability in deltaic and areas and is expected to increase by future sea level rise and soil subsidence. To preserve freshwater volumes and prevent increased agricultural damages mitigation measures needed to be taken. Saline groundwater extractions lower the saline groundwater interface and fresh water can percolate deeper into the subsoil, increasing the fresh water availability. The extracted water can be purified using reverse osmosis and be used as drinking water. This research investigated the geo-hydrological properties required to increase freshwater availability by applying saline groundwater extraction as a socioeconomic mitigation measure for salinization. Within the Zuid-Holland model different extraction scenarios were tested per polder area, to investigate the geo-hydrological properties. The agricultural damages and the phreatic water level decline were calculated with the WAOR and LHM model. To improve the freshwater availability extraction wells should be placed within saline seepage areas; to prevent saline seepage from bypassing the wells a high well density is needed. The extraction wells should be placed on the brackish-saline interface to prevent saline water from up-coning in the brackish groundwater. To prevent the area of dewatering and soil subsidence, no large phreatic water level decline should occur. A thick confining layer with a hydraulic resistance of at least 2000 days prevents this To obey the Dutch law a groundwater protection zone should be created which prevents pesticides from diminishing the water quality of the upper aquifer. The costs for drinking water production from the extracted groundwater (€0.93) are higher than conventional drinking water production methods therefore a division of costs between the stakeholders is needed.