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Assessment of contamination at Tiwai Point

New Zealand Aluminium Smelters (NZAS), located on Tiwai Point, announced in 2020 the intention of closing their operation by the end of 2024 due to financial challenges related to factors like electricity cost and declining aluminium prices. However, NZAS is currently negotiating a power deal to remain at the site.

After the announcement, Environment Southland has led a programme to ensure a comprehensive approach is taken to understand the state of contamination and to develop a contemporary monitoring programme and remediation standards for the smelter site and surrounding environment.

In assessing the extent of contamination at Tiwai Point, Environment Southland first built on its existing compliance monitoring programme in relation to discharges to air, land, groundwater and coastal waters. Additional activities developed include analysing the detailed site investigation (DSI) report released by NZAS; developing an independent Coastal Marine Area monitoring programme; analysing the environmental monitoring report on the impact of operations in the coastal marine area around Tiwai released by NZAS, among other activities.

Environment Southland and key stakeholders with regulatory and other interests in the Tiwai site come together regularly to ensure oversight of the Tiwai programme delivery to promote integration, coordination, and consistency in their related activities. Members include Te Runaka o Awarua, Te Rūnanga o Ngāi Tahu, Invercargill City Council, Ministry for the Environment, and the Department of Conservation.

Our assessment of NZAS’s Detailed Site Investigation report

Environment Southland engaged EHS Support to review NZAS’s DSI report and provide ongoing technical advice to the council.

The EHS Support assessment found many data and information gaps in the DSI report, including that it didn’t address the wider receiving environment, and the landfill and SCL pad areas. EHS Support recommended further investigation.

EHS Support’s key findings of NZAS’s report include:

  • Surface soil concentrations of PAHs (polycyclic aromatic hydrocarbon) and fluoride above health risk criteria and ecological screening criteria
  • Fluoride recorded at 8-16% concentration in surface soil in select areas
  • Groundwater contaminated with “elevated levels” of fluoride, aluminium, arsenic, PAHs (hydrocarbons), and cyanide
  • Stormwater drains sediment contains “elevated levels” of fluoride, aluminium, PAH, and heavy metals.
  • Concentrations above generic or default risk-based criteria, above commercial/industrial and recreational health risk criteria, and ecological screening criteria, but there was not enough information available to establish if the contamination was impacting on the surrounding terrestrial and marine environment.
  • Indications contaminants from storage and other infrastructure may be escaping into the surrounding environment. More information was needed about the current landfill, the storage area for spent cell liners (SCL) waste containing cyanide and toxic levels of fluoride, measurements of contamination blown or washed from the facility to surrounding land and water, and historic onsite measurements.
    See the full EHS Support Assessment here. https://www.es.govt.nz/repository/libraries/id:26g...

Media release: Tiwai Point: Assessment shows significant contamination #1https://www.es.govt.nz/about-us/news?item=id:2jf83uvxj17q9svaprzc

Media release: Tiwai Point: Assessment shows significant contamination #2https://www.es.govt.nz/about-us/news?item=id:2jf84n2g21cxbyp1to3q

Environment Southland’s Independent Coastal Marine Area monitoring programme

Environment Southland commissioned EHS Support to independently monitor the impact of any contaminants from the Tiwai aluminium smelter to the adjacent coastal marine area early 2023. The monitoring programme was consulted with and endorsed by tangata whenua.

The objective of the independent monitoring was to start addressing the gaps related to the coastal marine area, the closed landfill and the spent cell liner pad in the data received from NZAS in the DSI report to increase our understanding of the impact the smelter was having on the receiving environment.

The monitoring included sampling and analysis of:

  • Sediment and porewater (free water contained in pores in sediment particles on the seabed that is also linked with the groundwater. Porewater is the water that molluscs, like cockles or bottom swimming fish, come in contact with) and sea water from the intertidal area of Bluff Harbour (down gradient of the north, west and south drains on the Tiwai site) and Foveaux Strait, adjacent to NZAS’ key operations (landfill, ouvea storage, spent cell liner pad areas).
  • Sediment, sea water and soil conditions from background samples located in Bluff Harbour, Awarua Bay and Foveaux Strait areas.
  • Groundwater from selected wells adjacent to the coastal marine area

Media release: Independent monitoring begins around Tiwai smelterhttps://www.es.govt.nz/about-us/news?item=id:2kvkoplxp1cxby7yc4la

Some of the sampling methods used in the independent monitoring programme conducted January-February 2023 are shown as follows.
This full report can be read here: https://www.es.govt.nz/repository/libraries/id:26g...

​Warren from EHS is assisted by Andrea our Tiwai consents liaison Lead to collect a sample of porewater.

Warren from EHS is assisted by Andrea our Tiwai consents liaison Lead to collect a sample of porewater. This water is found between the sediment particles on the bed and beaches of the Tiwai Peninsula and is linked to the groundwater. Porewater is the water that molluscs, like cockles or bottom swimming fish, come in contact with. It is effectively syringed out before being sent for analysis.

Key findings from EHS Support’s independent monitoring of the coastal marine area surrounding Tiwai smelter site in early 2023 include:

  • Widespread groundwater contamination: sources of contamination within operational areas of the smelter have generated widespread groundwater contamination that is discharging into the coastal marine area.
  • Contamination levels lower than expected: the scale and nature of the contamination recorded are less than expected due to the nature of the receiving environments attenuating contaminant discharges.
  • Low risk of bioaccumulation: there are unlikely to be higher-order or human health risks via contaminant bioaccumulation through the food chain, although further testing is needed for more definitive conclusion.
  • Extensive landfill contamination plume: the extent of the groundwater contamination plume discharging from the landfill to Foveaux Strait is extensive (approximately 1 km wide), and its effects are being assessed through the landfill’s reconsenting process.
  • Stormwater drain discharges above limits: discharges of contaminants occur via the consented stormwater drains at levels exceeding environmental screening values, posing potential chronic and, at times, acute effects to ecological receptors.
  • First flush stormwater discharges beyond mixing zones: first flush stormwater discharges from the north drains extended beyond the mixing zones at concentrations greater than environmental screening values and consented limits. Sediment and pore water concentrations above environmental screening values also extend beyond the mixing zones of the north drain.
  • Groundwater discharges exceeding screening values: groundwater discharges are occurring within the smelter domain and SCL pad areas that exceed groundwater environmental screening values.
  • Ecological risk from soil contamination: soil contamination along selected foreshore areas investigated recorded contaminant concentrations that could pose a potential terrestrial ecological risk.
  • Under reporting of stormwater sampling: the consent stormwater sampling is potentially under reporting contaminant concentrations beyond the mixing zone during certain flow conditions and does not address sediment or pore water contamination within the drains and broader receiving environment.
  • Public access concerns given the ease of public access to Bluff Harbour and the discharge points for the stormwater drains, measures should be implemented to warn the public.
  • Media release: Remediation plan needed to address Tiwai contamination

NZAS’ developments on the peninsula

Listed below are a series of developments that have occurred with the objective of achieving improved environmental outcomes.

  • In March 2022, ES asked NZAS to cease unauthorised discharges of contaminants to land/water relating to fluoride contamination at two areas. NZAS provided a written proposal in July 2022, and completed the remediation required in late September 2022. Contamination source material now being processed at a more secure location onsite.
  • NZAS provided a summary of the network of groundwater wells that exist on the peninsula.
  • NZAS drilled 45 new bores in the smelter site and 5 in the DOC land in the first quarter of 2023, to be included in their monitoring programme. ES suggested including 7 of the 45 bores to cover strategic locations.
  • NZAS extended the analytical suite of tests as part of the closure study to help better understand the extent of contamination on site and better understand the hydrogeology of the site.
  • NZAS relocated the Ouvea from 5 storage locations around Southland to NZAS site. The Ouvea was stored into containers and exported overseas.
  • In May 2023, NZAS lodged the application for consent for the Tiwai landfill.
  • In July 2023, ES visited the smelter site to verify the conditions of the drain clearing process. The activity appeared to be compliant with the rule.
  • In August 2023, ES visited NZAS site to check the bath process. The Environment Southland project team identified that NZAS had implemented housekeeping practices to prevent dust dispersion over the operation areas. The team has also encouraged NZAS to implement stormwater improvements e.g. extensive drain cleaning programme.
  • ES had requested NZAS to erect signage at the discharge points to alert the public of the industrial discharges. The signage was installed on the 15th of December 2023.
  • NZAS is currently doing some field trials of oyster shells to work on the drain issues identified on receipt GHD and EHS Support reports.
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