Salvors have been unable to find any trace of 22 containers known to be carrying contaminants that were on the stern of the Rena when it sank off the Bay of Plenty.
In a statement today, the group still working on the clean-up said scientists from the Cawthron Institute, working with the Rena recovery monitoring team, would be carrying out further sampling and testing of water and sediment samples.
"This will then confirm possible solutions to remediate contaminated areas, currently known to be in close proximity to the wreck," Captain John Owen of insurers The Swedish Club said.
The Rena grounded on Astrolabe Reef in October 2011, and last January split in two, with the back section gradually sinking.
Most of the bow section of the container ship remained above the water level, and was being removed to one metre below the low tide mark by salvage company Resolve Salvage & Fire.
A decision has yet to be made on what will happen with the remainder of the wreck after that work is done.
The salvage group said a dive survey of the sunken stern section and its cargo had been completed.
Of 36 remaining containers that had been carrying known contaminants in the stern section, many had broken up and their contents had escaped, the salvage company said.
Three containers, with cargo intact, had been recovered, four were retrieved but were empty, while another seven were recovered in pieces. The contents of the remaining 22 containers were presumed to be lost to the sea.
Resolve said it was using specialist heavy-lifting equipment to remove the large amounts of remaining cargo along with wreck and container debris from an area of about 10,000 square metres around the ship. In the past month, more than 256 tonnes of debris had been removed.
That work would enable scientists to undertake a more detailed study of the surface of the reef to help determine what, if any, contaminants remained trapped, the salvage group said.
Two containers of plastic beads were possibly still trapped by scrap and debris within the stern section. Work to remove that debris would allow Resolve to determine how to deal with the beads and any identified contaminants.
Owen said studies of the environmental, cultural, economic and safety impacts of the different options for dealing with the wreck were nearly finished.
A further round of community consultation would be held in late February, before a final decision was made.