Marin Municipal Water District seeks $200K grant for desalination study

Marin Municipal Water District is seeking a $200,000 federal grant to study the possibility of building a brackish water desalination plant on the Petaluma River.

The district’s board voted 4-0 on Tuesday, with Jed Smith abstaining, to retroactively authorize an application to the U.S. Bureau of Reclamation for the study. The district submitted the grant application in late February.

While the district has studied a desalination plant on San Francisco Bay in the past, officials said a plant in brackish water on the Petaluma River is a newer concept that has not been examined.

“There is not a lot of real data,” Paul Sellier, the district water resources director, told the board on Tuesday. “And we need to get that data so we can present information to you so that can make an informed decision one way or another.”

The grant application is one of several actions the district is taking in its exploration of new water supplies to weather future droughts. Earlier this month, the board approved a “roadmap” of potential projects it could pursue, including expanding reservoir storage, desalination, increasing conservation incentives and maximizing imports from the Russian River.

The list resulted from a nearly yearlong study that began during the recent drought, when the district and the 191,000 residents it serves faced the possibility of depleting local reservoir supplies as early as mid-2022.

Unlike previous tests of desalination of bay water near San Rafael, the Petaluma River plant would be located in shallow, brackish water south of Petaluma. District staff said treating brackish water would require less energy, would reduce costs and produce less brine waste as a result of the lower salt concentration compared to bay water.

The district study estimated the project could cost $122 million to nearly $194 million to construct and produce about 5,325 acre-feet of water per year for the district at a cost of $1,800 to $2,900 per acre-foot.

For comparison, the district’s seven reservoirs hold about 80,000 acre-feet of water, which is about a two-year supply. The cost to treat reservoir water ranges from roughly $300 to $450 per acre-foot.

The estimated yield from the desalination plant would be comparable to adding a second Bon Tempe Reservoir, which is the district’s fifth-largest reservoir and can store about 4,000 acre-feet of water.

Ben Horenstein, the district general manager, said there is still a “fair amount of uncertainty” about the potential water yield and brine discharge of such a facility, which the study would seek to address.

The estimates assume that the district would share the plant with the North Marin Water District, which serves the greater Novato area.

The federal grant application has received support from Petaluma and the North Marin Water District. The grant would require the Marin Municipal Water District to make a matching contribution of $200,000, which would need to be approved by the board.

Past efforts by the district to explore desalination have been controversial among ratepayers. The efforts led to litigation and the passage of a voter initiative in 2010 requiring ratepayer approval before such a plant would be allowed to be built. The proposed study would not require voter approval, according to the district.

Concerns raised about desalination include its significant costs, its energy requirements and the environmental effects of brine waste. Supporters state it would provide a reliable source of supply during droughts. The water district tested desalination twice in the past 30 years, using pilot plants on the bay in 1990 and from 2005 to 2007, but shelved the idea in both cases.

Smith abstained from Tuesday’s vote based on staff noticing and procedural concerns about the grant proposal.

“My abstention from the vote did not lean into the merit of wanting to understand this more,” Smith said during the meeting.

Staff told the board that it had been eyeing the grant since January and had already submitted an application in February. Smith said he and some other board members were only notified about the details of the grant shortly before the meeting Tuesday.

“I feel like we’ve had a lot of pushback from our community about study after study that we just approve, and this one we haven’t even actually reviewed and it’s been on the desk for two months,” Smith said.

Horenstein said the board gave direction to pursue all grant opportunities, but that the board does not need to accept the grants if awarded or approve any matching funds.

While recognizing Smith’s concerns about the noticing, other board members supported the grant application.

“None of the items that are on the roadmap are going to move forward without additional studies,” Ranjiv Khush said.

“This is the kind of work we need to do,” Matt Samson said, “and if we can get someone else to help us contribute to that, it allows us to spend our money in other ways exploring other options.”

In addition to the desalination project, the district has submitted an application for $1 million to the U.S. Environmental Protection Agency to expand wireless meter installation to 2,000 homes in disadvantaged communities. About 5,000 wireless meters have been installed in the district’s service area in central and southern Marin. The meters allow ratepayers and the district to see water use data immediately.