Residents will now have more time to have their say on Nature Calls with more than 300 submissions already received.
It is Palmerston North's biggest financial and environmental decision for many years, with consultation being extended until July 10.
Consultation began in early June and was scheduled for the month.
Nature Calls is focused on determining the best practicable option for treating the city's wastewater for up to the next 35 years.
At present the city's wastewater is treated for around four days before being discharged into the Manawatū River.
But the Palmerston North City Council's consent is ending soon, and a new consent is required by mid-2022.
Six options for how the council could do this in the future are being consulted on.
During the consultation, some residents have asked for more information about the environmental impact of the options.
That impact won't be fully understood until the treatment level is determined, locations chosen and more scientific investigations take place.
As part of the resource consent application, the council will also be required to undertake an Assessment of Environmental Effects (AEE).
At this stage, the council is working with information it has gathered from expert knowledge, and building on as progress is made through to a preferred option.
The council will be undertaking detailed work next year on the preferred option, which is when it prepares the AEE.
On Thursday night, new information will be added to naturecalls.nz to explain how the council narrowed down the selection of potential options from 36 to six.
Council chief infrastructure officer Tom Williams says many of the options didn't make it to the consultation stage due to the large costs, or because they wouldn't meet other public health, cultural, environmental or recreational standards.
These options were given a fatal flaw status.
"This information may help people understand how we narrowed down the options.
"We don't expect this additional information will sway people's views, but those who've already made submissions will be able to make a new submission if the information does impact their earlier thoughts," he said.
"We will be emailing those who've made submissions to let them know about the extra information."
Those who've already made a submission, and want to alter it, are asked to fill in a new submission form at naturecalls.nz or the written form from the consultation guide which can be found at all Palmerston North libraries, or the council's customer centre.
Williams says when the new submission is received the council will be able to give an update.
He added that because it is the most important project, residents needed to have their say.
"We need to get as much feedback as possible, and we are aware some residents have not received consultation material in their letterboxes.
"That has been remedied, with most homes now having received consultation material over the past few days."
The consultation material is all online at naturecalls.nz and at all council public libraries.
People can also ring the council call centre to request a consultation guide and it will be hand-delivered.
Two additional drop-in sessions will be held this Saturday, July 4, to allow people to talk to the project team one-on-one.
The team will be at the Ashhurst Library from 10am-11am and then the City Library from 11.30am-12.30pm.
Ashhurst is having a second drop-in session as that is the area most affected by not receiving consultation material.
In early August the council will advise residents of key findings from the consultations.
This information will be on naturecalls.nz, the councils Facebook page and emailed to everyone who makes a submission.
In December, the consultation feedback will be presented to the council alongside technical reports focused on a range of environmental, social, economic and cultural factors.
Elected members will then choose which option to proceed for the resource consent.