CONSTRUCTION IS COMPLETE on the first experimental levee along the San Francisco Bay shoreline that will clean treated wastewater and discharge it into the Bay. Now, all that’s needed is for the levee to be plugged in to the source of treated water.
On Wednesday, officials invited press to visit the Palo Alto Horizontal Levee Pilot Project, which sits between the Regional Water Quality Control Plant and the upland marshes of the Baylands in the lower south of San Francisco Bay.
What’s experimental is the way the levee is engineered. The top layer is a thick, loamy clay soil covered in native plants. Treated effluent, or cleaned wastewater from the treatment plant, will flow from beneath the surface in a dense layer of gravel and sand. The plants will stick their roots down into it and get water that way.
The magic happens when those plants clean all the extra fertilizer, pharmaceuticals and contaminants from the wastewater discharge, leaching cleaner water into the Bay.
The pilot horizontal levee in Palo Alto will only absorb .1 million gallons of water out of the 20 million gallons of wastewater treated at the plant each day. But it is an important model that might be used in other cities around the Bay to meet new standards.
This summer, the San Francisco Regional Water Quality Control Board required all the Bay Area’s 37 wastewater treatment plants to reduce sewage in their effluent discharges by 40% over 10 years. The move followed harmful algal blooms in the Bay in 2022 and 2023 that caused massive fish kills. The price tag for the facility upgrades was estimated to be $11 billion, or $4,000 per household, according to the board.
Left: An illustration of the Palo Alto, Calif., horizontal levee project. Horizontal levees utilize a gently sloping, vegetated ecotone slope to provide multiple benefits beyond wave attenuation including refugia habitat, enhancement of transitional habitat between tidal wetlands and terrestrial uplands, sea level rise adaptation, and treated wastewater polishing. Right: A conceptional design of a horizontal levee. Horizontal levees utilize a gently sloping, vegetated ecotone slope to provide multiple benefits beyond wave attenuation including refugia habitat, enhancement of transitional habitat between tidal wetlands and terrestrial uplands, sea level rise adaptation, and treated wastewater polishing. Palo Alto, Calif., is currently conducting a horizontal levee project. (City of Palo Alto via Bay City News)
Last year, the Bay Conservation and Development Commission released a Regional Shoreline Adaptation Plan, which includes guidelines to fulfill the requirements of Senate Bill 272, a new state law that requires each local government to submit a sea level adaptation plan to the BCDC by 2034.
Samantha Engelage, senior engineer at the Regional Water Quality Control Plant in Palo Alto, said the project’s key goals are to restore transitional marsh habitat, or grassy areas where tidal waters flood and drain intermittently. Other goals include helping to adapt to sea level rise, providing marginalized communities a way to engage with the landscape through interpretive signage and educational materials, and maintaining public access through the Bay Trail, a 350-mile bicycle and footpath that will eventually circle San Francisco Bay.
“Lastly, but not least, we want to use this site to polish our treated wastewater,” said Engelage.
The Palo Alto treatment plant does a good job of treating the wastewater, she said, so the extra cleaning that happens through the levee is a bonus.
Project timeline and next steps
The project started back in 2018 and is expected to be complete in late spring 2026.
Engelage said the facility which will provide water to the levees is undergoing construction. Most of the levee work is completed, she said, and they are currently doing plantings, but the city still must construct the pipeline to get the treated wastewater out there.
The total cost for the pilot levee was $7 million. That included $4.8 million in construction, about $15,000 in permit fees and $500,000 for permit enforcement.
“It’s an innovative design and it paves the way for future projects,” said Heidi Nutters, principal program manager for the San Francisco Estuary Partnership, which is managing the design and engineering of the project. “We’re managing the money and then the city of Palo Alto is the committee that manages the project.”
Nutters said they received funding through the U.S. Environmental Protection Agency, as well as the state Coastal Conservancy, the city of Palo Alto and other partners.
Outside on the levee, Jessie Olson, habitat restoration director for the nonprofit Save the Bay, oversaw a group of volunteers planting native grasses and scrub on the newly formed levee.
“We are watering the plants today,” she said, referring to the construction delay. “Most all of the plants have nice, healthy root systems. When we plant in the winter and fall, we’re giving them the longest chance to develop deep root systems and survive our dry Mediterranean climates.”
The plants will grow tall because they will be irrigated by treated wastewater, as they have at another horizontal levee. In 2015, the city of San Lorenzo built a closed-system prototype. It was a 400-foot-long green slope that also received treated wastewater delivered through pipes buried deep under the levee. Plants and grasses above removed waste nutrients, pharmaceuticals, metals and trace contaminants at a surprisingly successful rate. The San Lorenzo levee does not discharge into the Bay. The Palo Alto levee will.