Waste water disposal at the Nesjavellir geothermal power plant, apparent problems and possible solutions

Abstract

Geothermal fluids, brought to the surface by geothermal power plants, usually contain higher chemical concentrations and higher temperatures than those found in surface environments. The chemistry of the fluid discharged is largely dependent on the geochemistry of the reservoir and the operating conditions used for power generation, which varies from one geothermal field to another. The toxic compositions available in most high-temperature geothermal waters include: chloride (Cl), aluminium (Al), boron (B), arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg), and sometimes fluoride (F). Samples, for major and trace element analyses, are collected twice a year at discharge areas between the Nesjavellir power plant and Lake Thingvallavatn. This paper reviews the monitoring on both chemical and thermal variations over the last 30 years, including periods both before and during the power plant’s operation. It discusses present waste water disposal methods and their effectiveness. Finally, suggestions are presented to fulfil both environmental standards and to prevent operational disruptions. The results show that a correlation exists between the neighbouring sites around the shoreline of the lake, and that maximum temperature at the Varmagjá site has decreased by 1.5°C from 2006 (after reinjection started in 2004 and a cooling tower was installed in 2005).