Posted on June 26, 2018
By Tim O'Connell, stuff
The clean-up of one of New Zealand’s most contaminated sites is now complete.
The $8.9 million remediation project of Port Nelson’s Calwell Slipway came to an end last week, winding up an eight-year process to fix pollution caused by years of shipping repair work that used toxic substances.
Project manager Kelly Leonard, of Port Nelson, was pleased to have the task finished with only minor weather delays and maintenance hampering the progress of the remediation team.
Leonard said the project would come in under budget.
“It was pretty complex, but now we’re at the end and we have a successful delivery.”
The Ministry for the Environment’s Contaminated Sites Remediation Fund (CSRF) provided 50 per cent of the project’s funding.
The slipway site was ranked number two on the CSRF list prior to the project.
Marine sediments around it were contaminated by pollutants such as tributyltin and copper from ship repair work dating back to 1970.
The remediation project between the port and the Government was established in 2010, and work began in October last year.
The project, managed by Port Nelson and carried out by Auckland-based civil engineering contractors Heron Construction, used excavators and dredging equipment to dig up the contaminated sediment.
It was mixed with concrete and bound with activated carbon to form “mudcrete”, which contained the pollutants, before being returned to the seabed.
The final 1000m3 was dredged in April.
Last week Heron Construction completed site disestablishment and restoration of the slipway and surrounds, finished off with rocks being placed on the reclamation face.
Target concentrations for residual sediments in the Calwell Slipway Basin were 270 mg/kg for copper and 0.07mg/kg for tributyltin.
Sampling at the conclusion of site works showed 42mg/kg for copper and 0.039mg/kg for tributyltin.
The second remedial objective was to restore navigability to the Calwell Slipway Basin which had not been dredged since 1984.
Post-dredge hydrographic survey indicated that charted depths have been restored and exceeded in many locations within the basin.
A new 5000m2 reclamation was constructed east of Kingsford Quay adjacent to the slipway.
Leonard said the reclaimed land would be paved in spring to be used for additional logging storage
Speaking to Stuff in December, Port Nelson chief executive Martin Byrne said the construction of the reclamation was a “win-win” for the port in cleaning the slipway as well as creating extra land to reconfigure logging areas.
Leonard said the slipway would remain on the CSRF website until it was updated with the next funding round announcement.
From the port’s perspective, however, it was mission accomplished.
“In terms of monitoring, there’s not much there to monitor so we don’t have any ongoing obligations,” Leonard said.
“The contamination was likely not only limited only to use from the slipway, more of a general area – but now all discharges from the slipway are contained and disposed of appropriately … and with the worldwide ban on [tributyltin], we’re not seeing it in circulation anymore.”
Source: stuff
