Gisborne sewer blockage clearance on hold pending Friday decision

No activity on the water at the confluence of Gisborne city rivers Taruheru, Waimata and Tūranganui on Thursday afternoon. In the background are waka stacked up at the Marina. This number will be significantly reduced as local paddlers head to Lake Karapiro for the Waka Ama Sprint Nationals, starting on Sunday. Training was curtailed by health warning signs going up after the district council had to open the emergency sewer valve at the Oak St pump station earlier this week, discharging raw sewage into Taruheru River, after a sewer pipe backed up due to green waste being put into a manhole on a Mangapapa property.

Contractors dealing with the sewer blockage caused by garden waste dumped down a manhole in the Mangapapa area have paused work and will re-evaluate the situation on Friday.

The clearance work has been on hold since Wednesday while contractors wait for the flow in the sewer pipe to drop.

The emergency sewage discharge valve at Oak St was opened for 12 hours on Monday night, pouring raw waste into the city rivers again.

Gisborne District Council (GDC) said the cause of the blockage that prompted the discharge was someone cutting up garden waste and putting it down a manhole.

The cost so far to the council has been about $25,000, according to the social media comment from GDC. It includes generators, a crane, disconnecting the power, a jetting unit, suction units and pumps, a camera, health and safety for teams working in confined spaces, and vehicles.

Health warnings on the city rivers and beaches remain in place until Sunday.

“They have located the blockage and crews have been working hard to unblock it,” the council said.

“The contractors have been waiting for the flow in the sewer pipe to drop so they can so they can put a camera into the pipe.”

Workers pictured on site earlier this week. Clearance work for the sewer blockage in Gisborne has been on hold since Wednesday while contractors wait for the flow in the sewer pipe to drop. Photo / Murray Robertson

A GDC statement on social media late Wednesday said the blockage could not previously be shifted or broken up by a high-pressure water blaster.

“Yesterday the jetting did move the blockage along the pipe but then it got stuck further along. The team suspect a branch re-wedged in the pipe again. The section of pipe is 239m long and 375mm wide (about the size of a toilet seat).

“The camera arrived, but the water level’s still too high and sewage is muddy coloured so we can’t get a photo of the blockage until the water level drops.”

A council spokesperson said the clearance work had to be abandoned as the sewer was still in flood and more rain was expected again overnight on Wednesday and Thursday.

“A decision will be made Friday on when clearance work can recommence.”

Steps have been taken to ease the pressure on the sewer pipeline that services Mangapapa.

The council reminded residents that wet wipes, nappies, clothing, rags, towels, fat and oils, food waste, rubbish, garden waste, and anything medical or personal should not go into the sewer pipe.

According to the Land Air Water Aotearoa website, enterococci sampling taken at Waikanae Beach, Grey St, on Monday showed 1100 colony-forming units per 100 mL (CFU/100ml) compared with 670 CFU/100ml measured Thursday last week and 120 CFU/100ml on December 30.

When the levels of enterococci bacteria per 100 mL are more than 500, the estimated risk of illness is more than 10% from contact with the water.