The Freshwater Resource Of Andros Island, Bahamas, Determined By Resistivity

The freshwater lens on Andros Island, Bahamas, is an important source of potable water for local<br>use and for export to the city of Nassau on New Providence Island. The production of large quantities of<br>water for export raises concern for the long-term sustainability of the resource. Resistivity soundings<br>provide a relatively easy way to evaluate and monitor the thickness of the freshwater lens. This<br>technique works well because there is a large contrast in resistivity between the freshwater and saltwater<br>saturated carbonate rocks that make up the island. Over the last 8 years we, along with students from<br>our universities, have conducted a number of resistivity surveys across the northern part of the island. A<br>number of problems, which complicate the acquisition of resistivity soundings on the island, will be<br>presented. Working around these problems we have developed a profile of the freshwater lens across<br>the island.<br>Our results show:<br>a single lens spans the island from Red Bays on the west to Conch Sound on the east,<br>the lens averages about 15 m thick over much of the island,<br>the lens thins to about 8 m under the well field areas, and<br>the lens thins to about 10 m in the vicinity of Charlies Blue Hole.