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Assessment of contamination at Tiwai Point

Contamination at Tiwai Point

Environment Southland is leading a programme of work to ensure a comprehensive approach is taken to understanding the state of contamination and to developing a contemporary monitoring programme and remediation standards for the smelter site and surrounding environment.

Scientific monitoring and analysis to date shows the Tiwai smelter is a large contaminated site with numerous legacy and ongoing sources of contamination to the environment. Monitoring undertaken in early 2023 confirms that most of the contamination discharging from drains and ground water into the surrounding coastal marine environment is well above ecological risk levels. There was lower than expected residue in seawater and sediment, likely due to the swift currents of Foveaux Strait dispersing and diluting contaminants. This means there is unlikely to be human health risks via contaminant bioaccumulation through the food chain.

NZAS is working cooperatively with Environment Southland, including providing ongoing access to the site for site visits and environmental sampling.

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.

Background

New Zealand Aluminium Smelters (NZAS) is currently negotiating a power deal and has signalled its intention to remain at the site. However, in 2020 it announced it would close its Tiwai Point operations by the end of 2024.

Following the announcement in December 2020, David Parker, the then Minister for the Environment, asked Environment Southland to investigate the extent of the contamination at NZAS' Tiwai Point site and made funding available to support the investigation. Understanding the extent of the contamination is important for assessing what is needed to clean up and remediate the site during operations and when/if it closes.

The aluminium smelter at Tiwai Point is one of the largest industrial sites of its kind in New Zealand. Due to the monitoring and data analysis work, Environment Southland now has a fairly good understanding of the extent of contamination at Tiwai Point. This work is ongoing and complex. Everything Environment Southland does needs to be technically robust and within the legal and regulatory framework.

With any long-standing industrial operation of NZAS’ magnitude some level of contamination at the site is to be expected.

Environment Southland will publicly share information about our work relating to the smelter, so long as doing so does not affect our regulatory role as a regional council.

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. This enhanced programme was informed by advice from environmental consultants, Aurecon and EHS Support. In January 2023 independent monitoring was undertaken by EHS Support, a consultancy with international experience in decommissioning smelters, and it has provided two report, which are now publicly available on our website (links below).

Independent monitoring – coastal marine area

Environment Southland commissioned EHS Support, consultant smelter experts, to independently monitor the impact of any contaminants from the Tiwai aluminium smelter to the adjacent coastal marine area. This was initiated in January 2023 and completed in February 2023.

An earlier expert assessment by EHS Support of an NZAS report about contamination at the site had noted “numerous legacy and ongoing sources of contamination to the environment” and key gaps in the data. The gaps related to the surrounding coastal marine area, the onsite 50-year-old landfill (now closed) and the on-site spent cell liner pad.

The objective of the independent monitoring was to start addressing the gaps in the data to increase our understanding of the impact the smelter was having on the receiving environment.

EHS Support designed the independent monitoring programme in consultation with tangata whenua and undertook the monitoring.

The monitoring included sampling and analysis of:

  • Sediment and porewater (free water contained in pores in sediment) 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 smelter

Report – coastal marine area

The full report can be read here.

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

  • Sources of contamination within operational areas of smelter have generated widespread groundwater contamination that is discharging into the coastal marine area.
  • The scale and nature of the contamination recorded is less than expected as the nature of the Bluff Harbour and Foveaux Strait receiving environments both attenuate contaminant discharges to varying degrees.
  • There are unlikely to be higher order or human health risks via contaminant bioaccumulation through the food chain. This determination requires further biological testing to provide a more affirmative conclusion.
  • The extent of the groundwater contamination plume discharging from the landfill to Foveaux Strait is extensive (approximately 1 km wide) with the effects from this discharge currently being assessed through the re-consenting process for the NZAS landfill.
  • Discharges of contaminants occur via the consented storm water drains (above environmental screening values) posing potential chronic and acute effects to ecological receptors.
  • There are first flush stormwater discharges from the north drain that extend beyond the mixing zones at concentrations greater than environmental screening values and consented limits. Sediment and pore water concentrations above environmental screening values extend beyond the mixing zones of the north drain and are not captured by the consent.
  • Groundwater discharges are occurring within the smelter domain and spent cell liner pad areas that exceed groundwater environmental screening values.
  • It is clear that concentrations exceed ecological screening values within the coastal marine area to the west of the landfill (in Bluff Harbour).
  • Soil contamination along most foreshore areas investigated recorded contaminant concentrations that could pose a potential terrestrial ecological risk (notably south and west drains, east landfill area, Inalco area, and spent cell pad area).
  • 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.
  • 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.

Note: a request has been made to NZAS to erect signage at the discharge points to alert the public of the industrial discharges.

Media release: Remediation plan needed to address Tiwai contamination

The images, below, demonstrate some of the sampling methods used in the independent monitoring programme conducted January-February 2023. The monitoring was undertaken by smelter experts EHS Support. While it looks simple, a lot of effort and planning goes into quality control to ensure the samples are representative of the coastal marine area.

Warren from EHS is assisted by Graeme, our Tiwai technical lead. This piece of equipment was specifically brought in from the USA to collect long core sediment samples, efficiently. Its motor drives a long tube down into the ground, which is then leveraged out, with the sediment intact. In this demonstration only a short core was extracted.

​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.

Our assessment of NZAS’s site report

NZAS provided Environment Southland with a Detailed Site Investigation (DSI) report prepared by its consultants GHD, in August 2021. The DSI report provides information about the contaminants found at the aluminium smelter site on Tiwai Point and is helpful in informing Environment Southland’s work.

Environment Southland engaged EHS Support, an environmental consulting company with international experience in smelter closures, to review NZAS’s DSI report and provide ongoing technical advice to the council.

The EHS Support assessment of the report found many data and information gaps in the DSI report, including that it didn’t address the wider site. 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.
  • A lot of data necessary for a full assessment of historic and current contamination across the smelter complex was missing, including exclusion of the landfill, SCL pad and wider receiving environment.

The data from NZAS is only a preliminary snapshot of the recent state of the site, the nature of the receiving environment, and some detail on contamination levels and was not considered a Detailed Site Investigation report by EHS.

See the full EHS Support Assessment here.

Media release: Tiwai Point: Assessment shows significant contamination #1

Media release: Tiwai Point: Assessment shows significant contamination #2

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