Regional council consents manager Alex King said the request covered "a number of technical and planning matters".
"The information request is in line with the scale of the activities consent is being sought for," Ms King said.
The city council’s landfill at Green Island is only consented to operate until October this year.
Nevertheless, it is expected to be used until the city’s next landfill at Smooth Hill becomes operational in 2028 or 2029.
The letter from the regional council said the city council had until Wednesday to respond with the additional information.
The more than 100 follow-up questions by the regional council covered a range of topics.
Among the outstanding planning matters to be addressed, the city council needed to provide an assessment that showed the landfill would provide a regional benefit or there was no workable alternative.
It asked for further details on what type of sediment discharges were expected in Kaikorai Stream and estuary during earthworks at the site.
There were questions around how the landfill capping and leachate collection system would work.
There were also further questions around proposed odour mitigation measures, groundwater quality and landfill gas.
When the consent application was made, the city council said its present estimate was that the Green Island landfill could remain in operation for an additional six or seven years.
