Partially treated sewage spills into Waikato River

A power outage at Hamilton City Council’s treatment plant has led to 129,400 litres of partially treated wastewater being released into the Waikato River.

The spill occurred on Thursday afternoon after Hamilton’s only wastewater treatment facility, Pukete Wastewater Treatment Plant, experienced a localised power cut. This led to 129,400l of wastewater halfway through processing being discharged into the river.

Council staff have advised Waikato Regional Council and iwi, and will be monitoring the impact on the river, if any, in the coming days. An investigation is under way into the cause of the power cut.

Hamilton city water manager Maire Porter said the power outage occurred at 2.36pm and the bypass event started at 2.47pm. Everything was back online and working again by 4pm.

‘‘We had a localised power outage which we believe was caused by a car hitting power lines in the area but we have not had that confirmed by Wel or police,’’ Porter said. ‘‘That power outage caused all wastewater processing equipment to stop working for around 90 minutes.

‘‘This meant we had what we call a secondary bypass occur, which is where partially treated wastewater where the solids have been removed, basically bypassed the final stages of treatment and was discharged into the Waikato River.’’

The secondary bypass would have had all solids removed and would have gone through a biological process to remove dissolved and suspended organic compounds in the water. This would make it ‘‘unnoticeable’’ in the river. ‘‘We have got continuity plans in place should this occur.

‘‘We add chlorine as an additional treatment to the discharge, and we also set up generators and divert flow on to onsite storage as much as possible to minimise any discharge into the Waikato River.’’

Porter said staff would be conducting ongoing monitoring to see if there was any detectable impact.

While being exposed to partially treated water is not harmful, as a precautionary measure council advises people to stay out of the water nearby the plant for the next few days. ‘‘There is no visual impact that we have seen which is great but we have notified a number of downstream river users to let them know and be aware of what happened, so they can do what they think is necessary.’’

This is not the first time the treatment plant has experienced a spillage issue.

In 2012, the city council was convicted and discharged, and ordered to spend $37,500 on river plantings and fencing after discharging 90,000l of partially treated sewage into the river during an incident in July 2011. ‘‘The Waikato River is a precious resource to everyone including Hamilton City Council,’’ Porter said. ‘‘We never like it when something like this happens.’’