Assessment of geothermal wastewater disposal effects : case studies ; Nesjavellir (Iceland) and Olkaria (Kenya) fields

Abstract

Every geothermal installation produces a unique set of chemical effluents, which depend intricately upon the geochemistry and the exploitation history of the hydrothermal reservoir and on the individual plant design. Potentially adverse effects of geothermal energy utilization are chemical, -from gaseous components in steam that are discharged into the atmosphere and from aqueous components in spent water-, and physical in the form of thermal stress, particularly in aquatic ecosystems. An environmental assessment of potential effects of current geothermal wastewater disposal options in the exploitation of the Nesjavellir geothermal field (Iceland) and the eastern sector of the Olkaria geothermal field (Kenya) is made. At Nesjavellir co-generation power plant hot wastewater 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. Also an assessment of thermal stress at lake shoreline outflow sites was done....