The Influence of Effluent Water Discharged from the N·mafjall Geothermal Field on Local Groundwater

Abstract

The N·mafjall geothermal field has been produced for the last thirty years. The effluent water has been discharged at the surface and there is concern about the possible effect on the extraordinary nature in and around Lake M?vatn only two km away. Tracer tests made in the early 1980ís indicated a relatively slow groundwater flow from the site of the geothermal field towards Lake M?vatn. On the other hand there is a rapid surface flow observed in open fissures in the area to the south and west. Recent tracer tests using potassium iodide and fluorescent dyes support this indicating that the effluent flow is partly along fissures and partly a slower groundwater flow system. Up to º of injected iodide tracer had been recovered within two weeks. The iodide tracer test reults point to an extended dilution and mixing within the groundwater system.