Wanganui District Council carried out a survey of the sludge at the bottom of the city's wastewater treatment plant on Wednesday.
The plant has been malfunctioning since early December, when an excessive amount of solid waste entered the plant. That has caused an unpleasant smell to spread over the city for the past month.
Two other dumps of material from local businesses have happened since then.
Council infrastructure manager Mark Hughes said the survey had been due to take place on Monday but was delayed because of strong winds.
He said the purpose of the survey was to assess whether the depth of the sludge had reduced enough to enable some of the plant's aerators to be turned back on.
The council did not respond to questions about whether the aerators had, in fact, been turned back on but Mr Hughes said samples from the survey would be sent for testing, with results likely next week.
Horizons Regional Council issued the council with an abatement notice on Wednesday, warning it to get rid of the smell within four weeks or potentially face further action.