Independent monitors are investigating the impact of any contaminants from the Tiwai Point aluminium smelter on the surrounding coastal marine area.
New Zealand Aluminium Smelters recently commissioned a report into contamination, but it has since been found to have key gaps in the data including for the onsite 50-year-old landfill and the coastal marine area.
The assessment, undertaken by EHS Support, also noted numerous legacy and ongoing sources of contamination to the environment.
Environment Southland chief executive Wilma Falconer said the goal of the monitoring was to determine whether there were any contamination issues.
"While it is the smelter's responsibility to remediate the contamination, it is the Council's responsibility to set the standard of that remediation," Falconer said.
"To be able to do that we need to understand the level of contamination and its potential impacts and these investigations will help us to do that."
EHS Support is also doing the independent monitoring, which will include sampling and analysis of sediment and seawater from the intertidal area of Bluff Harbour, sediment, sea water and soil conditions in Awarua Bay and Foveaux Strait, and groundwater from selected wells near the coastal marine area.
The work started last week and should take a month to complete before the results are analysed and publicly available in the first half of the year.
"We are pleased to be getting this next phase of our work programme under way. It is really important because it will give us an indication of any further contamination at the site and in the wider environment," Falconer said.
Minister of Environment David Parker requested an investigation into the extent of the contamination.
New Zealand Aluminium Smelters uses an extensive network of wells to monitor groundwater quality and has recently added 46 new wells including eight at the request of Environment Southland for additional monitoring.
It holds eight discharge and water consents with the regional council and the council said it has been complying with its monitoring and transparency requirements.