Steady-State Approximate Freshwater–Saltwater Interface in a Two-Horizontal-Well Scavenging System

Abstract

In this study, an approximate mathematical formulation is derived to delineate a steady-state freshwater–saltwater interface by a horizontal scavenger well system in a confined aquifer that consists of two horizontal pumping wells. One horizontal well is above the freshwater–saltwater interface to recover freshwater. The other horizontal well is below the interface to extract saltwater. A set of dimensionless variables are introduced to facilitate solution derivations. Critical pumping rates that correspond to critical upconing and downconing interfaces are then derived for two different interface extents. Finally, the horizontal scavenger well system is applied to a real-world case, the 1,500-foot sand in Baton Rouge, Louisiana, and is compared to the current vertical scavenger well system, where the Field-Critchley analytical solution is adopted. The real-world case study demonstrates that among many advantages, the horizontal scavenger well system can recover more freshwater and extract less saltwater than the vertical scavenger well system. The study also indicates that the current freshwater and saltwater pumping rates are far below the safe zone and that freshwater is pulled into the saltwater well.