How much sewage can San Diego recycle? To keep Pure Water on track, city slashes capacity, eyes Lake Murray - The San Diego Union-Tribune

Pure Water: City rethinks sewage recycling, eyes Lake Murray - The San Diego Union-Tribune

To avoid delaying the launch of the system, the city will start out recycling less sewage than planned. Storage for phase two might shift from San Vicente Reservoir to the much closer Lake Murray.

With phase one of San Diego’s Pure Water sewage recycling system nearly half built, city officials are making major adjustments to plans for constructing the rest of the system in order to avoid delays and potentially shrink overall costs.

To cope with severe flooding at the Morena Boulevard pump station that threatens to delay the start of operations by more than a year, city officials now plan to temporarily recycle only 40 percent as much sewage so they can start on time in mid-2025.

Slashing the daily capacity from 30 million gallons to 12 million gallons will allow the city to cut the Morena Boulevard pump station out of the recycling system until it can be activated in late 2026 — at least a year behind schedule.

City officials are also seeking state approval to permanently revamp phase two of Pure Water, which is scheduled to begin operations in 2035. Officials want to revise plans to pump recycled sewage 20 miles from the phase two purification plant in Mission Valley to the San Vicente Reservoir.

Instead, the city wants to use only the much closer Lake Murray near La Mesa, which would eliminate the need to spend hundreds of millions building many miles of pipeline to San Vicente and could shrink the number of pump stations needed for phase two.

But city officials say much of those savings would be eaten up by the need to treat the water more thoroughly because Lake Murray is much smaller than San Vicente Reservoir, requiring a more rigorous type of purification.

Those changes were endorsed last week by the City Council’s Environment Committee during a public hearing where city officials gave a comprehensive update on Pure Water, the largest infrastructure project in San Diego history.

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Construction crews are simultaneously working on 10 different projects that make up Pure Water phase one, which will cost nearly $1.2 billion total.

The projects include pump stations, reclamation plants, a purification plant in western Miramar, nine large tunnels and 30 miles of pipeline through Clairemont, Bay Park, University City, Miramar and Scripps Ranch.

Pure Water 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 once completed, which is currently expected in 2035.

Phase one is expected eventually to produce 30 million gallons per day of potable drinking water. Phase two is slated to produce another 53 million gallons a day.

The city ran into significant problems shortly after construction began last year when a contractor trying to build a large sewage-pump station on Morena Boulevard was forced to halt work because of constant flooding.

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After multiple attempts to solve the problem failed, city officials agreed last August to spend $20 million building a large dam-like structure around the area being flooded, which is north of Friars Road near Custer and Sherman streets.

Crews completed the dam, formally called a secant wall, this month. But the project has put construction of the Morena pump station more than a year behind schedule, jeopardizing the timing of the whole Pure Water system.

The project’s 10 components need to work together like a well-choreographed ballet, so it’s crucial for each of them to stay on schedule, city officials said.

To avoid delaying the start of recycling by more than a year, officials unveiled last week a plan to launch operations on a smaller scale and then ramp up to full operations when the Morena pump station is ready.

Officials say there is enough sewer water produced in the northern part of the city for the purification plant to produce 12 million gallons a day of potable water during the initial phase, which will include the entire system except the Morena pump station.

But that pump station is key to increasing the system’s purification capacity to 30 million gallons a day eventually. It is slated to pump to the Miramar purification plant much of the sewage sent to the city’s Point Loma sewer treatment plant.

Amy Dorman, the city’s assistant director of public utilities, said it will be at least a year after sewage recycling is launched before the Morena pump station comes online and allows an increase from 12 million daily gallons to 30 million.

The possible shift from San Vicente to Lake Murray for Pure Water phase two would have a greater long-term impact on the system.

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

State approval is needed for the change because the recycled sewage would be pumped directly into the city’s water system at Lake Murray’s Alvarado water treatment plant, instead of into a reservoir where it could mix with rain and other natural water before being treated.

California hasn’t yet approved any sewage recycling systems that pump directly into the water supply without a reservoir. And Pure Water phase one will pump its recycled sewage into the Lake Miramar reservoir in Scripps Ranch.

But a new law requires the state to create comprehensive guidelines by the end of this year for pumping recycled sewage directly into water systems, which is called direct potable reuse. Pumping recycled sewage into reservoirs is called indirect potable reuse.

Dorman said city officials are optimistic San Diego will be the first water agency in the state to get approved for direct potable reuse, noting that state officials are using the city’s plans for Lake Murray as a model for the new regulations.

But a city analysis last year studied three options — using only Lake Murray for phase two of Pure Water, using only San Vicente and using both sites.

Dorman said the analysis made it clear there are many factors involved in what the city ultimately decides, including how the decision would affect the Alvarado treatment plant.

“We want to understand how sending that much water to Lake Murray would impact the Alvarado treatment plant operations,” she said. “That’s one piece of the big analysis.”

If only Lake Murray were used, the city would save hundreds of millions that would otherwise be spent building pipelines from Mission Valley to San Vicente Reservoir, which is between Lakeside and Ramona. And it would spare residents along the path of that pipeline the inconvenience that would come with many months of construction.

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

But the savings would likely be only marginal, said Dorman and Ally Berenter, the city’s senior manager of external affairs and water policy.

That’s because Lake Murray isn’t nearly large enough to store all the recycled sewage the Mission Valley purification plant is slated to produce, which means the recycled water would have to be pumped directly into the water system and would make the project direct potable reuse.

That would require two extra and expensive steps in the purification process, because the recycled sewage wouldn’t be diluted in a large body of water.

San Vicente Reservoir is large enough to store all the water from Mission Valley, allowing the three-step purification process already allowed under indirect potable reuse — instead of five steps.

Under both options, the costs for Pure Water phase two would be in the neighborhood of $3 billion, with the Lake Murray version costing somewhat less. But Berenter stressed that estimated costs for a project that won’t be built for 12 years are vulnerable to big changes.

While costs for Pure Water are significant, city officials stress that without the project, San Diego would also have to spend an estimated $3 billion upgrading the Point Loma plant and the outfall that it uses to dump treated sewage into the ocean.

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