Discharge of mercury from the Wairakei geothermal power station to the Waikato River, New Zealand

Abstract

The Wairakei geothermal power station on the west bank of the Waikato River 10 km north of Lake Taupo, New Zealand, discharges a warm mixture of cooling water and geothermal steam condensate to the river. This discharge contains at least two chemical species of mercury (Hg flows out of Lake Aratiatia, the reservoir formed for the Aratiatia hydro-electric power station 3 km down-stream from the Wairakei station. The residence time of the condensate in Lake Aratiatia varies between 1.5 h at high river flow and 12 h during winter when water is accumulated in the lake overnight. The warm condensate initially floats on the surface of the river but only a small proportion of the Hg 0 is lost to the atmosphere. Furthermore, the short residence time of the condensate in the lake probably limits the extent to which other mechanisms can remove Hg 0 from the river water. For these reasons it is concluded that most of the Hg 0 discharged to the river from the Wairakei Received 4 October 1996; accepted 24 March 1997 station remains as Hg 0 in the water flowing out of Lake Aratiatia. Fine-grained bed sediments in Lake Aratiatia are an insignificant sink for Hg because of their very small area and relatively low total Hg concentrations. It seems likely, therefore, that the non-reducible forms of Hg discharged with the condensate also remain in the river water and pass out of the lake. M96075

Measurement of Atmospheric Mercury over Volcanic and Fumarolic Regions on the North Island of New Zealand Using Passive Air Samplers

“…The Wairakei geothermal power station built in the Wairakei geothermal field is located ∼3 km northeast of Karapiti. Elevated GEM concentrations up to 2,200 ng m –3 have been measured in the air over discharges from the Wairakei geothermal power station . However, it does not appear that the GEM concentrations at Karapiti were influenced by Hg emissions from the station.…”

“…Elevated GEM concentrations up to 2,200 ng m −3 have been measured in the air over discharges from the Wairakei geothermal power station. 56 However, it does not appear that the GEM concentrations at Karapiti were influenced by Hg emissions from the station. Sites on the northeast corner of the field (K19, K25, and K31), closest to the power station, did not have elevated GEM concentrations.…”