Reshaping the Nicasio Reservoir is the most efficient way to add to the water supply in Marin, county water managers said.
A new cost analysis presented to the Marin Municipal Water District board this month showed that the $5 million project would provide significant supply gains for a relatively low cost when compared to other proposals under consideration — many of them tagged with estimates exceeding hundreds of millions of dollars.
The Nicasio project would modify the reservoir’s spillway gates to add 3,000 acre-feet of water storage. In drought conditions, it is anticipated to still produce 750 acre-feet of water a year. An acre-foot is about 326,000 gallons.
In a dry year, the cost per acre foot of water produced by the project would be around $1,093. By comparison, in a normal year the cost for drinking water purchased from Sonoma Water is around $1,600 an acre-foot.
“This is a really difficult project from a water supply perspective to make unattractive,” Paul Sellier, water resources manager said at a meeting on Dec. 10. “So even if the cost doubled on this project, this would still be sort of ranked as a very, very favorable project.”
Other projects that stood out in the analysis included potential pipelines from Petaluma or Cotati to Marin reservoirs.
Two options look at pumping water from Russian River to Soulajule Reservoir, while the other looks at building a pipeline system from water tanks in Cotati to a pipeline from Soulajule to Nicasio.
The projects range from about $168 million to $372 million to construct with supply gains from 3,800 acre-feet up to more than 8,000 acre-feet of water. What’s most appealing about the proposals is the cost per acre foot during drought conditions, which would be in the ballpark of $6,000, Sellier said.
The discussion was an update on the district’s water supply roadmap. The plan seeks to add another 12,000 to 20,000 acre-feet of annual supply by 2035.
Sellier’s presentation included updates on some short-term projects in the works, but the conversation largely centered around the latest cost estimates for all longer-term water supply proposals that are on the table.
That list includes more than a dozen potential projects, such as storage expansion, the creation of a desalination plant and new recycled water infrastructure.
A growing chorus of Marin ranchers are building on a protest against expansion of the Soulajule Reservoir, which they say would upend their livelihood.
As discussed to date, multigenerational homes and ranches could be threatened by the footprint of a bigger dam, requiring the agency to acquire land, likely by eminent domain.
Carol Dolcini, a rancher in the affected Hicks Valley community of West Marin, said there are projects other than Soulajule that “will achieve Marin’s water supply targets without destroying valuable agricultural land, and without placing undue financial pressure on Marin ratepayers.”
Expanding Soulajule would cost $484 million. That estimate includes allowances for engineering, environmental mitigation, land acquisition and construction, according to the Marin Municipal Water District.
“Our hope tonight is that we will all come to agree that have reached the end of the road for the Soulajule expansion option,” Dolcini said at the meeting. “It’s time to fine-tune the portfolio to include options that are both feasible and affordable.”
Expansion of Kent dam is expected to cost $519 million, while the creation of a new reservoir in an area called “upper” Nicasio, near the existing Nicasio reservoir, would cost $687 million.
Staff estimated the dam expansion projects would cost upwards of $7,300 per acre-foot of water, assuming drought conditions.
Desalination projects would be much more expensive, ranging from $352 million to $520 million in capital alone, with total annual costs expected to range from $27 million to $51 million. Assuming a four-year drought, it would cost $10,000 to $16,000 to produce an acre-foot of water through a desalination plant.
The analysis also looked at a range of recycled water options, with a potential project at Peacock Gap standing out as a viable contender. The project would cost about $28 million, but annual operations and maintenance would remain under $1 million.
“We need to remember that cost is but one criteria at which we look at projects,” Sellier said. “It’s a very important criteria, but it is just one criteria.”
Board members Ranjiv Khush and Jed Smith agreed that the Sonoma to Marin pipeline options look appealing.
Smith said the dam expansion and desalination projects appear too costly, and there is low hanging fruit with the Nicasio spillway project and potentially with the pipelines.
“I want to encourage this board to be a lot more direct,” Smith said. “We need to guide the staff to make some decisions. I see us in an emergency right now. We need to start taking things off the table and we need to focus our efforts and increase our water supply as soon as possible.”
Ben Horenstein, general manager of the Marin Municipal Water District, said staff received good feedback to help narrow its focus for the next few presentations aimed on building consensus on a preferred project.
In the coming months, staff expects to provide analyses exploring the social and environmental impacts of each proposal, as well as the risks and the estimated drought performance of each project.
