Marin water utility set to begin studies of new supply options

The Marin Municipal Water District is preparing to launch more in-depth studies of new water supply projects, beginning with assembling consulting teams.

The district board is set to vote on contracts with new consulting teams next month to begin preliminary technical, environmental and engineering studies of larger, more complex projects. The projects include expanding local reservoir storage, constructing a brackish Petaluma River desalination plant and installing new pipelines to transfer Russian River water directly into local reservoirs.

Unlike the broader study completed earlier this year that identified which of the supply options the district could pursue, the more in-depth analyses are needed to provide details on how and whether they can be built, as well as the costs and environmental impacts.

“There needs to eventually be a project you can say yes to, very specifically,” district consultant Xavier Irias told the board.

The district expects the studies to be completed between June and September 2024.

The district, which serves 191,000 residents in central and southern Marin, is preparing to significantly increase water supplies for the first time since the 1980s. The effort follows the 2020-2021 drought that threatened to deplete the utility’s seven reservoirs. Rains in late 2021 nearly refilled the basins and ended the crisis.

The seven reservoirs make up about 75% of the district’s water supply. The reservoirs can hold up to about 80,000 acre-feet of water, about a two-year supply. An acre-foot is about 326,000 gallons of water.

The remaining water is imported from the Russian River.

Following a yearlong study, the district adopted a water supply roadmap earlier this year that seeks to add another 12,000 to 20,000 acre-feet of annual supply by 2035. The study estimated the agency would need at least 8,500 acre-feet of additional water per year to weather a severe four-year drought.

The district adopted historic rate increases to help pay for the estimated $35 million it plans to invest in the projects through mid-2027.

Of the three longer-term studies, the proposal to enlarge reservoir capacity generated the most discussion among the board and staff. The district is studying the three largest reservoirs — Kent, Soulajule and Nicasio — for the potential of adding moveable spillway gates or raising spillways to add capacity.

“We’re looking at the costs, the impacts, the benefits, the timeline,” Irias told the board. “Those impacts could be across a wide range of concerns, whether it’s short-term construction impacts, impact on inundating a road and requiring it to be relocated.”

The biggest question about the proposal is how it would affect the district’s water rights. A 1995 order from the state water regulators says that any additional reservoir storage capacity the district creates must be used for environmental water releases for protected fish such as coho salmon.

“You can raise the dam but you have to release the water to the watershed,” board member Larry Russell said. “It’s mechanical. That’s what the current agreement says.”

Ben Horenstein, the general manager of the water district, said the staff plans to simultaneously consult with the state regulators on the proposed projects while conducting the feasibility studies for each of the reservoirs.

“We’ve tried to think about talking to the regulators first without that information, but that seems very problematic at this point given there’s so much we really don’t know and we’re also talking about different watersheds,” Horenstein told the board.

Monty Schmitt, president of the board, said he would prefer to consult with state regulators first to determine whether there are certain projects that would not trigger reopening the district’s water rights.

“I do feel that is a very fundamental issue that could have a very substantial change in what we are currently required to release,” Schmitt said during the meeting, referring to the environmental releases.

For the proposed brackish desalination plant near the mouth of the Petaluma River, Paul Sellier, the district’s water resources director, said Petaluma is set to release a report next month on preliminary well tests that could help determine the feasibility of such a facility. The district’s own feasibility report is expected to be released in June.

Meanwhile, work is underway on near-term projects that aim to improve the efficiency of the district’s existing water supplies. One project would automate environmental dam water releases using flow gauges as opposed to the manual process required currently. The project is meant to prevent releasing too much or too little water.

Sellier said the staff hopes to begin installing equipment at the end of October, followed by a yearlong calibration period.

Another project — a pipeline connecting Phoenix Lake to Bon Tempe Reservoir — is also set to undergo further study. Phoenix Lake is only drawn on during water shortages because it does not have a pumping and distribution system. To pump water, staff must undergo a four-week effort to set up a pump station and pipes to transport water to the Bon Tempe treatment plant. The new project would create a permanent pump station and pump water through a 1,200-foot tunnel into Bon Tempe Reservoir.

The district is also looking to add permanent pump stations to its third-largest reservoir, Soulajule. Like Phoenix Lake, the reservoir is only tapped during emergency shortages and requires the use of portable generators. Pacific Gas & Electric Co. says electric lines are the most feasible option to power the new facility and that alternative power such solar panels might not be cost-effective, according to Sellier.

Board members stated they would like to see more information from PG&E on how they came to that conclusion.

“It’s kind of a disappointment that PG&E is turning away with that,” board member Matt Samson said during the meeting.

“We seem like an optimal landowner and climate for solar,” board member Jed Smith said. “We have a long-term perspective. It would just be good to see the math.”