The Portland City Council approved plans for a $500 million water filtration plant in 2017. But now, more than two years later, Water Bureau leaders say the plant likely will cost 70% more, or $850 million.

That's because the original cost estimate did not include any pipes to carry water to or from the treatment plant. Planners did not disclose that omission to the council in 2017 or during the intervening two years.

Mayor Ted Wheeler appeared politely infuriated over it Thursday, noting the plant could never have operated without pipes leading in and out. Those are projected to cost $100 million to $200 million, and Water Bureau officials made it clear they think the higher-end system would be better for water quality and system reliability.

Overall, they recommended commissioners pick an $850 million version of a treatment plant, not a pared-back $730 million one or a “minimally compliant” $670 million one. All three of those options include pipes.

Wheeler upbraided Water Bureau Director Mike Stuhr for his agency’s lack of transparency when presenting the $500 million plan to the council before its August 2017 vote.

"It would have been very helpful for me to know that what we were talking about at that time was not the total project cost but merely one component of an overall system," Wheeler said. "We needed to know we were talking about a piece of the system that could not operate, work or function in any meaningful manner without the other component of the system."

Stuhr said planners at the time didn’t know what type or size of pipes they would need and hadn’t studied those issues or the costs. “Nobody’s pipe systems are the same,” he said.

Portland, which prides itself on its pure “Bull Run” water from a huge virgin watershed of the same name, does not treat its water other than to add chlorine and a chemical to reduce its corrosiveness. But in 2017, the federal Environmental Protection Agency and the Oregon Health Authority said that had to change because cryptosporidium was showing up too often in the city’s water samples.

Hence the 2017 vote to authorize construction of the $500 million filtration plant.

Officials said at the time that $500 million was a rough, early-stage estimate. They said the same is true of the new figures and showed that the $850 million version of the plant could end up costing as little as $600 million or as much as $1.25 billion.

Stuhr and other top bureau officials briefed Wheeler and commissioners Amanda Fritz and Jo Ann Hardesty about the new plans and costs projections Thursday. Commissioner Nick Fish, who oversaw the Water Bureau when the original cost projections were made, and Commissioner Chloe Eudaly were both absent from that work session.

In addition to revealing that the recommended treatment plant will require $200 million of pipelines, Stuhr and his team also said the projected cost to build the plant they envision sans pipes has risen by about $150 million to about $650 million.

Hardesty zeroed in most forcefully on the impact the ballooning costs will have on ratepayers. The typical residential customer would see their water and sewer bills rise an average of 9.2% a year to a peak increase of $10.91 a month in about 2028, Water Bureau finance director Cecelia Huynh told the commissioners.

Hardesty and the mayor both questioned whether that was an annual figure, only to be told it is monthly, translating to an extra $131 a year. “I need to understand why we are doing a Mercedes plant when requirement is minimum compliance. Why?” Hardesty asked.

Principal engineer David Peters’ rationale included that the new plant would meet full projected water needs, while a smaller plant would require expensive use of groundwater in some years; that having two pipes leading into and out of the treatment plant would allow the system to continue to operate in case of needed repairs or maintenance to the lines; and that longer pipes would increase the flow of water into the treatment plant and allow the bureau to discontinue use of some aging water-delivery conduits that are old and likely to break in the coming decade or decades.

The council will be asked to vote on the issue in October.