Practical methods of minimizing or mitigating environmental effects from integrated geothermal developments; recent examples from New Zealand

Abstract

Monitoring of the environmental effects of geothermal resource utilisation in New Zealand has confirmed the benefits of appropriate management in terms of production and reinjection strategies. Such strategies can minimise, reverse or mitigate the effects on surface thermal activity. This applies to direct use of low enthalpy resources as well as integrated use of high enthalpy resources. At Rotokawa, a strategy of deep productionand total shallow reinjection for an integrated steam turbine/binary power plant has resulted in a gradual enhancement of several chloride springs, with no significant detrimental effects. At Wairakei, less than 50% of the waste hot water is reinjected, but several users are able to take advantage of the separated hot water in a way that mitigates for the historic loss of geysers at Wairakei Valley. These include tourist facilities based on a geothermally-heated prawn farm, and hot stream restoration with an artificial geyser/silica terrace that was developed by local Maori. At Mokai, several years of production history from a binary/steam turbine, with shallow reinjection of brine and steam condensate, has not caused any significant environment effects on surface thermal features. At Rotorua, management of extraction and reinjection from numerous domesticbores has achieved a significant recovery in hot spring and geyser activity. Users of many other hot spring areas in New Zealand are also managed by application of regulatory control through policies and plans under the Resource Management Act. These plans are presently undergoing a process of industry-wide review and improvement, by addressing changes in the philosophy of environmental management.