Erosion a slippery slope
Coastal intruder: Seawater seeps into smelter site
Coastal erosion is starting to impact bores used to monitor groundwater at the New Zealand Aluminium Smelters site at Tiwai Point.
Reports released by the aluminium producer show seawater has started to intrude into an area where NZAS stores a highly toxic substance, and has flooded a bore used for monitoring groundwater, reports show.
However, monitoring of cyanide and fluoride concentrations around the site where spent cell liner, which is made up of carbon refractory bricks, shows levels have decreased in recent years, and the smelter says it is confident it is currently compliant with all of its consents and environmental obligations.
NZAS has released a package of reports containing results of extensive environmental monitoring conducted at Tiwai Point, and detailed plans for further monitoring that will be undertaken as part of its closure study.
The aluminium producer is due to close its smelter at Tiwai Point in 2024 and has begun a closure study to determine what is needed to clean up the site when the company leaves.
Chief executive and site general manager Stew Hamilton said based on the review work done and the interaction with regulators to date, NZAS is confident it is currently compliant with all of its consents and environmental obligations.
‘‘We want to make sure our community and the local and government officials who monitor our performance understand our planning process and the importance we place on our environmental performance.’’
In March, Environment Minister David Parker admitted no agreements are in place between the aluminium producer and the Government for the cleanup of the site once production stopped.
Parker has given Environment Southland $300,000 to undertake additional monitoring at the Tiwai site.
Hamilton said ‘‘as the closure study progresses we will continue to release information and upload it to our website so everyone who is interested can see first-hand our approach to environmental monitoring and the closure process.’’
The reports contain assessments of the groundwater surrounding the landfill site and spent cell lining (SCL) storage facilities, which were highlighted in a Treasury commissioned Aurecon report that was done to assist the Government in its negotiations with the company.
It also includes a sampling plan developed by GHD, an international environmental consultancy, as part of their assessment of any potential contamination of soil and groundwater across the site.
GHD’s report says its initial review identified potential contaminant sources across the site, and it is preparing a detailed site investigation as part of its contaminated sites work package.
A separate report, the SCL Groundwater Status 2020 report, says that the results from a bore in the midshore zone near a pad where spent cell liner is stored shows that seawater intrusion started to occur in early 2020 because of coastal erosion of the southern coast.
The rate of coastal erosion has been actively monitored since 2017, the report says.
The pad is located 85 metres from the beach, and bores have been drilled around it to monitor any leaching from the spent cell liner into the groundwater.
SCL is made up of carbon refractory bricks, which are used in the aluminium process for five to six years. They contain fluorides, cyanides and nitrides. There is 181,000 tonnes of SCL stockpiled at Tiwai, and the smelter says it is actively looking for a way to export it.
NZAS has also released a monitoring report of the company’s landfill, which contains carbon material, double-bagged man-made mineral fibres such as glass wool, asbestos, clean-fill and refractory bricks. It says groundwater monitoring bores surrounding the landfill show there is leaching of contaminants from materials deposited at the landfill into the surrounding groundwater.