More severe droughts are looming. Could Santa Rosa’s pioneering water recycling program help stave off disaster?

Homes and businesses across central Sonoma County generated more than 5 billion gallons of wastewater last year, enough to fill more than 7,500 Olympic-sized swimming pools. That sewage flowed into Santa Rosa’s regional treatment plant south of Sebastopol, where it was cleaned up and nearly all of it put to a second use.

About 4 billion gallons of recycled water was pumped north from the Llano Road treatment plant in a 41-mile pipeline and up a steep slope into The Geysers geothermal fields southeast of Cloverdale. There it was injected into the ground to generate enough clean, renewable energy for about 100,000 North Bay households.

The system also sent 788 million gallons of recycled water to 61 farms covering 6,400 acres that produce milk, hay, grapes and vegetables, along with 386 million gallons for urban irrigation in Rohnert Park and Santa Rosa, the two largest cities in the wastewater system.

Every drop of the recycled irrigation water — safe for everything short of human consumption and sanitized to a degree that eliminates the COVID virus — replaces a drop of potable water from sources sure to be strained as California moves into its third year of worrisome drought.

But the state’s water future is daunting, and could pose a fundamental challenge to Santa Rosa’s recycling system, which was born out of controversy in the 1980s and is now hailed by state regulators as a win-win that safeguards local waterways — the Laguna de Santa Rosa and Russian River — previously used for discharge.

For water-stressed parts of California, where winter snowpack and rains are proving increasingly scarce or unreliable, recycled water is likely to prove a key source not just for irrigation but household and commercial use.

The warning signs are already apparent: State water regulators on Tuesday signaled plans to reduce or suspend diversions along the Russian River and its tributaries in Sonoma and Mendocino counties as early as June. The moves would likely affect fewer than the 1,800 water rights frozen last year in the face of dangerously low reservoir levels.

Long-range climate forecasts call for even more severe and persistent droughts, making existing surface and groundwater supplies more tenuous, while California’s latest long-term water strategy calls making greater use of recycled water.

“Recycled water is a sustainable, nearly drought-proof supply when used efficiently, and the total volume of water California recycles today could triple in the next decade,” the 2020 California Water Resilience Portfolio said.

The 141-page document was issued in response to Gov. Gavin Newsom’s executive order in 2019 calling for recommendations “to enable water security for all Californians.”

It also called for streamlining regulations to expand use of nonpotable recycled water while “protecting food safety and the environment.”

The State Water Resources Control Board is currently funding $970 million in loans and grants for 12 projects that would provide about 62,000 acre-feet of recycled water per year for urban and agricultural irrigation and indirect potable use through groundwater recharge. An acre-foot is 326,000 gallons, enough for more than two households for a year.

California produced 728,000 acre feet of recycled water in 2020, up about 40% from 20 years ago. Santa Rosa’s 5 billion gallon production equals 15,344 acre-feet — enough to sustain 35,750 local households annually, or an average of more than 92,000 people.

Obstacles to tapping recycled water

Wastewater experts like to say all water on, in and above Earth is recycled and humans are using the same water as the dinosaurs.

But there are major constraints on how the modern system of sewage plants can respond, starting at Santa Rosa’s Laguna Treatment Plant, located about 2 miles southwest of the city limits.

It receives an average of 16.4 million gallons of wastewater a day from more than 225,000 residents and 6,500 businesses in Santa Rosa, Rohnert Park, Cotati, Sebastopol and parts of Sonoma County outside cities.

The water goes through a three-step, 15-hour treatment process that includes removal of solids, clarification and filtration through a 4-foot bed of granular coal. Finally, the water is disinfected with ultraviolet light, deactivating potentially disease-causing bacteria and viruses, used instead of chlorination.

Recycled water that receives tertiary treatment is deemed safe for irrigation of landscapes, pastures, playground and crops that are eaten raw.

The city says it recycles 98% of the wastewater flowing into the plant, and there’s obviously no desirable way to boost the flow. Successful conservation measures in recent decades have, in fact, reduced the total amount of water used by Californians — and the nation as a whole.

Those savings reduce the amount of water available for recycling, local officials noted.

Californians could further reduce urban water use by 30% to 48% by steps such as replacing inefficient appliances and installing low-water use landscaping, according to a Pacific Institute report last month.

The major constraint for more local water recycling is Santa Rosa’s collaboration with Houston-based Calpine Corp., the nation’s largest geothermal power producer, which operates 13 power plants at The Geysers, straddling the Sonoma-Lake county line in the Mayacamas Mountains.

Steam wells, some deeper than 2 miles, tap superheated steam from water in contact with hot, porous and permeable rock. At the surface, steam runs through pipes to the power plants, spinning turbines that generate 725 megawatts of green energy around the clock.

Under a contract with Calpine that runs until 2037, Santa Rosa is required to provide 90% of the targeted 4.6 billion gallons of recycled water a year or pay penalties.

Reduced deliveries are allowed for natural catastrophes, such as wildfire and earthquake damage, but current drought conditions would not trigger that provision because there is enough water to fulfill the contract, said Jennifer Burke, director of Santa Rosa Water.

“The Geysers provides a critically important piece of our wastewater treatment system,” she said. “We need it to dispose of our wastewater.”

Even if the city could curtail water delivery to The Geysers, it is prohibited from spraying more recycled water on farmland than the crops require, Burke said.

Calpine has so far shown no interest in renegotiating the contract, she said.

Officials ponder recycling costs, options

Santa Rosa’s last look at the prospects for expanding water recycling said it did not pencil out — “not cost effective for the foreseeable future,” according to the city’s 2020 Urban Water Management Plan.

Burke said it would cost tens to hundreds of millions of dollars to install the necessary pipes, painted purple to distinguish them from ordinary potable water pipes.

Even at its current historically low level for this time of year, 2,700-acre Lake Sonoma west of Cloverdale, the North Bay’s largest reservoir, holds a two- to three-year supply of water, she said. It has helped the region support growth while withstanding several droughts over the past four decades.

But city and county officials and water authorities are not downplaying the prospect of running low on drinking water around the North Bay, which has no connections to the state and federal water systems. Rainwater runoff into the Russian River watershed, along with groundwater, constitute the main supplies.

“We’re always looking at our options,” Burke said, noting that conservation, surface water, groundwater and recycled water are in play. “We’re planning for the future with additional dry years,” she said.

There are opportunities for expanded water recycling in the county’s northern reaches, including Healdsburg, Cloverdale, Dry Creek Valley and Alexander Valley, said Grant Davis, general manager of Sonoma Water, the dominant water wholesaler and a key player in recycling efforts over the past two decades.

“As (potable) water becomes more constrained, you have to look further, you have to be more innovative,” he said. “You need to work hard to make these projects pencil out,” including the prospect of tapping ratepayers for support.

Adding a fourth step to the wastewater treatment process to transform sewage into potable water is an option, Davis and Burke said, noting that it is already happening in the state.

“Everything is on the table.” Burke said.

Southern California program leads way

Orange County’s $481 million Groundwater Replenishment System, in operation since 2008, produces 100 million gallons of recycled water per day through an advanced purification process that includes microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide.

Two-thirds of the treated water is piped to recharge basins in Anaheim, replenishing groundwater that provides 75% of the water for more than 2.5 million Orange County residents — a system known as indirect potable water reuse.

Billed as the world’s largest potable water purification facility, Orange County’s system uses one-third of the energy required to desalinate seawater and half the energy needed to import water from Northern California.

No agency is currently allowed to produce recycled water for direct potable use, but the Water Resources Control Board is required by law to develop regulations for direct potable use — putting it into public water supplies — by the end of 2023.

The regulations will provide options to California communities “working to diversify their water supply portfolios in the face of recurring drought and climate change,” Rebecca Greenwood, a water board engineering geologist, said in an email.