Ecological risk assessment of Nesjavellir geothermal power plant wastewater disposal in lake Thingvallavatn in SW-Iceland

Abstract

Nesjavellir geothermal power plant is located in SW-Iceland southwest of Lake Thingvallavatn. Utilisation of the geothermal resource for production of electricity and hot water for district heating brings to the surface geothermal fluids with trace elements. The waste fluid is either pumped into shallow drillholes that connect to underground water or disposed of in the Nesjavellir stream, where it disappears into the lava and finds its way into Lake Thingvallavatn. Temperature and quantities of various trace elements were measured in the wastewater discharged from the power plant and at Eldvík, Varmagjá, Markagjá and Grámelur springs on the shore of the lake. Trace elements were also measured in samples of an aquatic plant (Myrophyllum alterniflorum), a gastropod snail (Lymnaea peregra), a fish (arctic charr Salvelinus alpinus), from lake sediments at Varmagjá and at a control station, Vatnskot, on the north shore of the lake. Hg is mostly lost to the atmosphere before it reaches the lake. Other trace elements are modified through chemical reactions and diluted to such an extent that there is little reason for concern except in the case of arsenic ...