The Cawthron Institute report advised the Dunedin City Council to determine the makeup of the liquid pollution to understand whether nearby plants and animals were at risk.
The council said yesterday those results would be publicly available by the end of next month.
"Additional eco-toxicology monitoring has been undertaken," a council spokesman said.
"This is still being compiled and is due to be submitted to the Otago Regional Council before the end of May."
The council is applying for consent to extend the life of Green Island landfill until about 2029 and then close it.
It is also applying to redevelop the site in to a "resource recovery park precinct", which will include an organics receivals building, an organics processing facility, a material recovery facility for mixed recyclables, a construction and demolition recovery facility, and a bulk waste transfer station for general waste.
The site is bordered by Kaikorai Stream, which then enters nearby Kaikorai Lagoon.
The Cawthron report, included among a raft of appendices for applications related to the resource recovery park precinct, said its assessment used passive sampling techniques and toxicity testing to assess the potential impacts from the leachate of the landfill on groundwater and surface waters.
The analysis showed there were sources other than the landfill contributing to some of the toxicity that showed up in the samples. Further, it said "the results of this study warrants some caution as they use data from a one-off sampling event".
However, it also noted the sampling did not include contaminants such as trace metals and the toxicity at the site would likely be found to be higher when these were taken into account.
Data from surface-water sampling showed toxicity at sites downstream of the landfill, "suggesting that toxic leachate is seeping out".
The groundwater samples indicated "a potential pattern of transport and distribution of the leachate from the landfill site", the report said.
It made three recommendations.
Establishing the chemical makeup of the leachate would identify its more toxic components and help to determine whether remedial action was required, the report said.
Ongoing monitoring of the aquatic environment would provide valuable information on the ecological impacts of the leachate.
Establishing other possible sources of pollution in the catchment would assist in effective management and protection of the area, it said.
