Présentations Colloques

Objectives- Groundwater exists as a freshwater lens which is the mass of fresh groundwater floating on an underlying mass of denser seawater in many islands and atolls. The pumping of groundwater often causes saltwater upconing on such an island. The objective of this study is to develop the pumping technique that would produce freshwater overlying saltwater without upconing of the saltwater and pollution of the freshwater zone.**Design and methodology- We made a device that installed a partition made of air packer in a borehole. The device also had two pumps. One pump was set above the air packer, and another pump was set under the air packer. By use of air packers, groundwater was pumped from one horizon and another horizon respectively. The device was set in the borehole of 100mm diameter with in the field of our laboratory, and groundwater was pumped. The length of packer was 1m, and packer was set at 2m below the groundwater table. The groundwater pumping ratio of two pumps was 1-2 liter minute respectively. EC, pH, DO, and ORP of groundwater that was pumped by the device were measured during the pumping. EC of groundwater drawn above packer did not fluctuate so much. The difference between EC of groundwater drawn above packer and EC of groundwater drawn from beneath a packer was kept. This result shows that the groundwater of two depth can be separately pumped with this device.**Conclusion- Scavenger well system can be constructed with air packer and two pumps in a well. This system has the advantage that packer's position can be freely set, and it is possible to follow to the change in the saltwater-freshwater boundary.