Marin water districts study options for new supply

Marin County’s two largest water utilities are working to narrow down what new sources of supply would provide the most benefit in droughts.

The North Marin Water District presented findings of a study looking at how to bolster supplies for the more than 60,000 residents it serves in its greater Novato service area.

The top scorers were projects to enhance the storage at the district’s Stafford Lake reservoir. Other options such as desalination, creating new reservoirs, dredging the lake and a major recycled water expansion were deemed too expensive or infeasible given the district’s size.

“We’re trying to maximize the amount of local water that enters the lake,” Tony Williams, the district’s assistant general manager, said during a public workshop on the assessment last week.

The Marin Municipal Water District, which serves 191,000 residents in central and southern Marin, is working to complete a similar study to determine how much water it needs to meet future demands and have more supply in major droughts.

The studies come months after the Marin Municipal Water District faced the prospect of depleting its reservoirs during the current drought and after the North Marin Water District experienced its driest winter on record in 2020-2021.

The North Marin district estimates its water demand will increase by about 26% in the next 25 years, from about 2.9 billion gallons per year to about 3.6 billion gallons. Population increase is the main driver of the larger water demand, according to the assessment by the West Yost engineering firm.

The study looked at new supply options that could provide another additional 326 million to 652 million gallons of water per year for the district.

The three highest-scoring options in the study were to reduce the waste of water during its treatment; to increase the capacity of Stafford Lake by installing an adjustable gate to cover its spillway; and to divert captured stormwater into the lake. Put together, the actions would produce an estimated 323 million to 516 million gallons within the next five years at a price ranging from $3.8 million to as much as $15 million, according to the study.

That doesn’t mean other options such as desalination are off the table for the district, staff said, but would likely be accomplished in cooperation with other water suppliers on the North Coast.

Only 25% of the North Marin district’s supply comes from Stafford Lake. The remainder comes from Russian River imports from the Sonoma Water agency. Sonoma Water is looking to complete a study on a variety of new water supplies, including groundwater banking, desalination and the potential to reduce environmental water releases for wildlife.

“The more you can do it at the regional basis rather than doing it individually by one agency to another is incredibly more powerful, more cost-effective,” Drew McIntyre, the district’s general manager, told the board of directors.

North Marin Water District board member Mike Joly said during the workshop last week that the district should be looking at desalination and emerging technology.

“I am glad that North Marin Water is going to be following up on the desalination concept, which is a long lead time and an expensive proposition,” Joly said.

Board member Rick Fraites called for the district to continue to explore creating a dam in Bowman Canyon, which the study estimated could provide up to 245 million gallons of water per year.

“It’s local, it’s right near our main water supply,” Fraites said during the workshop. “Maybe it’ll happen, maybe it won’t. Putting up a reservoir is a little dicey these days but I’d like us to take a harder look at that option.”

The Marin Municipal Water District plans to hold two workshops in the coming months to discuss water supply options and how effective they would be in various drought scenarios.