Geothermal Wastewater Disposal: Chemical Stress Assessment - Lake Thingvallavatn, Iceland

Abstract

Production of electricity and hot water for district heating by Nesjavellir geothermal co-generation power plant in SW-Iceland utilizes high temperature steam, which contains various trace elements. The effluent from the plant is either pumped into shallow drill holes or disposed off in the Nesjavellir stream, which disappears into the lava and finds its way into Lake Thingvallavatn, a rift lake of high conservational value. Measurement of quantities of chemical constituents in effluents and lakeshore outflow sites (springs), and in the biota at outflow sites, and at a control site, Vatnskot was done. Concentrations of SiO2, As, Al and B are elevated in geothermal effluents but are diluted before the wastewater reaches the lake. There is no detectable rise or accumulation of trace elements in the biota at the geothermally influenced sites. However, taking into account the conservational value of Lake Thingvallavatn, sound wastewater management by deep re-injection and regular monitoring of thermal influence, chemical constituents in effluents and lake outflow sites water should be adopted.