The Dynamics of Saltwater Upconing in Wells which Penetrate the FW-SW Transition Zone

Abstract:

Many freshwater aquifers have saltwater bodies in their deeper part. Such saltwater bodies may be a result of various processes, the most well-known of which is seawater intrusion. Studying the physical processes in the transition zone between fresh and saline waters in the aquifer is important since it can help in reducing risk of salinization of pumping wells.

Specifically, we study the effect of pumping from a well whose screen is submerged into the transition zone. Typically, wells are screened only against freshwater bearing strata, and the pump is installed close to the water table. However, if the screen of a production well extends below the freshwater body, and the well is screened against the transition layer between the two bodies, or even against the saltwater, the question is whether saline or brackish water will be pumped when the well is operated. It seems this problem has never been tested by scientific tools in the past.

A preliminary lab experiment and a preliminary numerical model revealed that the well screen may have an important role in the physical process of mixing. The flow through the fine mesh of the screen results in head loss. The head difference between the outside and the inside of the screen results in a ‘jump’ in the elevation of transition zone. This jump forces the freshwater outside the screen to flow through the screen slots in thin filaments into the saltwater, leading to enhanced mixing, in comparison to the case where no such head loss exists.