Enabling successful aquifer storage and recovery using horizontal directional drilled wells (HDDWs) in coastal aquifers

Aquifer storage and recovery (ASR) of freshwater surpluses can reduce freshwater shortages in coastal areas during periods of prolonged droughts. However, ASR is troublesome in saline coastal aquifers as buoyancy effects generally cause a significant loss of injected freshwater. The use of a pair of parallel, superimposed horizontal wells is proposed to combine shallow ASR with deep interception of underlying saltwater. A shallow, fresh groundwater lens can thereby be enlarged and protected. This freshmaker setup was successfully placed in a coastal aquifer in The Netherlands using horizontal directional drilling to install 70-m-long horizontal directional drilled wells (HDDWs). The freshmaker prototype aims to inject a specific volume of freshwater and abstract the same volume of water (consisting of injected water and ambient native groundwater) within the targeted water quality. Groundwater transport modeling preceding ASR operation demonstrates that this set up is able to abstract a water volume of 4,200