Resistivity Measurements And Modeling In The Vicinity Of A Trench Well

On North Andros Island, Bahamas, an extensive array of trench wells has been dug to collect<br>fresh water from the surface (unconfined) aquifer for export to Nassau. There is concern that salt<br>water will upcone below the trenches if water is withdrawn too rapidly. Resistivity soundings are<br>a common method for determining depth to the fresh-salt water interface. Where the soundings<br>are most important, the normal assumptions of resistivity sounding interpretation methods fail<br>because of the presence of the open, water-filled trench.<br>To interpret the soundings in the vicinity of the trench, the finite differences ground water<br>modeling program, MODFLOW, was reinterpreted to model the electrical flow. The resulting<br>models and several forms of resistivity soundings are compared and evaluated to assess their<br>usefulness in this unusual setting.