A major hiccup during the early construction stages of San Diego’s Pure Water sewage recycling system will cost the city at least $20 million — and potentially much more if it delays completion of the interdependent system’s other key components.

Constant flooding of a site off Morena Boulevard where a contractor is trying to build a large sewage-pump station has forced the contractor to halt work while city officials make plans to build a large dam-like structure around the area being flooded.

The need to build the dam not only will delay construction of the pump station and swell its cost from $110 million to $130 million. It could also delay other key parts of Pure Water, such as $200 million in pipelines and a $350 million sewage-purification facility in western Miramar.

Each of the project’s 10 components will need to work together like a well-choreographed ballet, so it’s crucial for each of them to stay on schedule, said James Nagelvoort, director of the city’s Strategic Capital Projects Department.

“This is the pump station that grabs all the sewage,” Nagelvoort said. “Without this pump station, you can’t capture that sewage and bring it on up (to the purification facility).”

Work on Pure Water, the largest project in city history, will kick into high gear soon

The flooding problems come just as construction kicks into high gear on Pure Water, the largest infrastructure project in city history. Neighborhoods across northern San Diego have been bracing for disruptions this summer and fall caused by tunneling and pipeline construction.

Pure Water is a sewage recycling system that aims to boost local water independence in the face of more severe droughts caused by climate change. It is projected to produce half the city’s drinking water when complete, which city officials estimate will happen in roughly 2035.

Phase one, including a sewage purification plant in western Miramar, will produce 34 million gallons per day of potable drinking water. Phase two, slated to include a purification plant in Mission Valley, will produce another 53 million gallons a day.

Contractor Flatiron West spent several months trying to solve the flooding problem at the Morena Boulevard site, which is north of Friars Road and just south of the intersection of Custer and Sherman streets.

They increased the size of piping, wells and pumps they were using to push out underground water so they could build the pump station, which must extend 43 feet below ground level, city officials said.

After months of delays and turbulence, sewage purification pipeline ready for construction in north part of city

Those efforts increased the amount of water being pushed out of the site from 860,000 gallons per day to 1.1 million gallons per day — the equivalent of two Olympic-sized pools. But the site, which is next to the San Diego River, was still too flooded to construct the pump station.

City officials say they considered three options to solve the problem and eventually chose the dam-like structure — a secant pile wall with jet grouting — based on a combination of costs and the likelihood of success.

Nagelvoort noted that a similar solution was used to allow expansion of San Diego International Airport just a few miles away. He didn’t guarantee the dam would work, but said he was confident.

“In essence, you are building a dam around the structure that you’re going to build,” he said. “It’s not perfectly watertight, but it’s certainly much better.”

Site near SDSU river park would recycle 53 million gallons of sewage per day, far more than Pure Water phase one

The City Council unanimously approved $20 million last week to pay for the dam.

Councilmember Joe LaCava praised Nagelvoort for finding a solution and being open about the challenges the city is facing.

“This is the right way for us to move nimbly and transparently forward,” LaCava said.

Councilmember Vivian Moreno said she wants the city to hold accountable whoever is responsible for putting the contractor in the impossible situation of building a project on a constantly flooded site.

“This is a very expensive error,” she said. “It’s clear we had inaccurate information regarding the water table.”

Nagelvoort said consultant AECOM, a construction engineering company, erroneously estimated that it would be adequate to pump 860,000 gallons per day out of the site.

“We are investigating whether their effort in design was below the standard of care and whether they have an obligation” to pay the city damages, he said. “I don’t know that yet. We’re still going through their work. We’ve actually brought in a geotech firm to help us review.”

Nagelvoort noted that AECOM and the city wasn’t able to access the site when the evaluation of the water table was conducted.

The additional costs may be passed on to the city’s 275,000 sewer and water ratepayers. The first phase of Pure Water will cost well over $1 billion.

City officials stress that without the project, the city would have to spend an estimated $3 billion upgrading the Point Loma Wastewater Treatment Plant and the outfall it uses to dump treated sewage into the ocean.

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