The revised cost estimate has been outlined in an upcoming Wellington City Council committee meeting agenda.
Some of the reasons given for the cost difference include construction inflation, changing seismic risk requirements, and having to construct the pump station deeper to keep out of the way of the Let's Get Wellington Moving transport plan.
Wellington Water network development and delivery group manager Tonia Haskell said having to work around existing roads, buildings and services added complexity, disruption and risk to the project.
"Early estimates for funding purposes before a project scoped is fully developed will always be subject to subject to change. Estimate increases associated with Covid-related materials and construction costs are impacting all infrastructure projects at this time."
Planning and Environment Committee chairwoman councillor Iona Pannett said some of the reasons for the cost difference appeared valid.
"But obviously we need to cost things properly because it just doesn't look good, does it? It has quadrupled."
Wellington City Council officers have recommended bringing forward some money in the long term plan to cover the additional $18 million.
However, the overall budget for wastewater won't increase - some of that money will just have to be borrowed sooner.
That's because there's a pool of funding in the budget that has been tagged for wastewater capital expenditure, but without a great level of detail for specific projects yet.
City councillors will consider the cost at a meeting on Thursday.
