Perth desalination plant’s impact “still uncertain”

The West Australia government’s Environmental Protection Authority has concluded that the significance of impacts to the marine environment from the discharge of brine by the Perth Metropolitan Desalination Plant is still uncertain and that the marine environment of Cockburn Sound continues to be under stress.

It is therefore recommending against lifting the set of dissolved oxygen trigger-levels which aim to ensure that relevant environmental standards are not exceeded.

The Water Corporation, whose plant was officially opened in April 2007, has been seeking for more than a year to have the trigger levels, which caused the plant to be shut down twice in the early months of 2008, removed as a condition of the plant being closed. The corporation says in its submission to the EPA that comprehensive studies had proved that the change in dissolved oxygen levels were the result of natural behaviour in Cockburn Sound during calm conditions and that the operations of the desalination plant had no impact.

EPA chairman Dr Paul Vogel said on 25 May 2009 that the setting of a minimum dissolved oxygen saturation bottom level of 60% and the trigger levels of the operational licence combined to satisfy the Environment Minister’s request in terms of providing a recommended set of dissolved oxygen trigger levels to ensure that Cockburn Sound standards were not exceeded.

The EPA recommended a further monitoring regime to be reviewed in another two years.

Water Corporation chief executive Sue Murphy said that, because the exhaustive tests by the University of Western Australia’s Centre for Water Research had demonstrated that there was no evidence that brine discharges from the desalination plant were having an adverse impact on the waters of Cockburn Sound, it was unreasonable to have shut-down conditions that were triggered by proven natural behaviour.

She said that the EPA in its recommendation focused solely on very unlikely environmental possibilities, suggesting that, in the final decision on the corporation’s application to have the trigger levels removed from its licence, the Minister for Environment, as the final decision-maker, should also take into account social and economic factors.

The EPA has been informed that the Department of Environment & Conservation intends to modify the existing operational licence subject to the outcome of the EPA’s review. Murphy said the Corporation would decide on its course of action in the next few days.