ORC senior consents planner Shay McDonald said evidence for an upcoming hearing suggested it was "reasonably likely" toxic liquid, known as leachate, was leaving the landfill and entering the Kaikorai Stream.
On the condition environmental monitoring was stepped up, Ms McDonald this week recommended consent be granted for the continued use of the city’s tip, its closure and then its aftercare.
"There remains uncertainty about whether, and to what extent, leachate may be migrating off-site and entering surface water; however, there are two lines of evidence that suggest that this is a reasonably likely scenario.
"Consent conditions are recommended which will ensure that the monitoring well network is expanded, additional information is obtained and interpreted, and measures to avoid or mitigate the effects of leachate are implemented if adverse effects are observed."
The cumulative effect of leachate potentially entering the degraded Kaikorai Stream and Estuary had not been satisfactorily addressed to date, she said.
But the proposed additional monitoring could be used for a revised Human Health and Environmental Risk Assessment in three years’ time.
"Three years’ additional data will provide data certainty of the risk to human health and the environment."
The Dunedin City Council’s consent to operate the Green Island landfill expired in October 2023, but the Resource Management Act (RMA) allows for consent holders to continue to exercise existing consents while applying for replacement ones.
A two-day hearing is scheduled for next month.
In a report published this week to help the RMA hearings process next month, Ms McDonald said she agreed with the DCC that continued use of the landfill at Green Island was better than the alternative options of incineration and out-of-district disposal.
Given the landfill must remain in its current "unfavourable" location, she also agreed there was "no reasonable alternative" to its continued use.
She reviewed the evidence of seven specialists due to present at the hearings and said on balance the actual and potential effects of the landfill on the environment would be well managed by conditions on the consent.
The DCC plans to use the Green Island landfill until the end of this decade when its successor, the planned Smooth Hill landfill south of Brighton Beach, is due to be operational.
