The Marin Municipal Water District’s water supply projects cannot be implemented in stages as staff had hoped.

Staff presented an update on their pipeline projects to the Works Committee at its meeting Friday. The update included construction cost estimates for three water transportation options and updates on how they might be built.

“I think it’s exciting,” said county board member Larry Russell, chairman of the committee. “But the costs are staggering, so I don’t know where we’re going on that part.”

The utility is currently exploring whether to connect pipelines in Petaluma and Cotati to its reservoirs to bolster its supply. The pipelines would transport treated water from the Russian River to Marin reservoirs through a 9-mile aqueduct along the Highway 101 corridor from Petaluma to the North Marin Water District in Novato. The district would send the water to the Marin Municipal Water District’s distribution system.

In April, the district chose three potential projects from a list of 13 possibilities. One option is to build a pipeline from the San Marin Drive area past Stafford Lake to the Soulajule Reservoir.

Initially, staff believed the project could be implemented in phases, with phase one building a pipeline from Soulajule Reservoir to Stafford Lake and phase two building the connecting pipeline to the NMWD aqueduct system.

However, due to concerns about water velocity, water pressure and water quality, phased construction is not considered feasible. Constructing the two phases simultaneously would cost the district approximately $137 million.

“It’s really not designed to support that use,” said Paul Sellier, manager of the Marin Municipal Water District. “To make this a meaningful project, we need to build phases one and two.”

A final phase would involve building a pipeline from Soulajule Reservoir to Nicasio Reservoir. The cost would be about $31 million. Construction of the entire project – including pumping stations, contracting and emergency preparedness – would cost about $167.4 million. The pipeline would be 16.4 miles long.

The North Marin Water District aqueduct can carry about 23 million gallons of water per day. Currently, MMWD receives 8 million gallons of water per day through the Ignacio Pumping Station and NMWD receives 4.5 million gallons per day.

With the new pipeline, winter water discharge could be 10.4 million gallons per day, but Sellier said that could be just an average and there could be days when the district uses 15 million gallons per day.

“Remember, this is a winter project, so these are the typical winter flows through this pipeline,” Sellier said.

The district is considering two other options, but both have similar problems to the first, as they would require multiple pumping stations and have limited construction options. A preliminary power assessment found the first option to be the most viable.

An alternative is to connect pipelines to the North Marin Water District’s aqueduct system by building a pipeline across San Antonio Road to the Soulajule Reservoir. Later phases would build a pipeline system from the water tanks in Cotati to Kastania Road and then connect the new Soulajule pipeline to the Nicasio Reservoir. This would add 14.8 miles of pipeline, cost up to $340 million, and increase supplies by more than 30 million gallons per day.

Finally, the county could build a pipeline connecting water tanks in Sonoma County to the Soulajule Reservoir. The project would include a new pipeline along the Highway 101 corridor through Petaluma to the reservoir. In the next phase, it would be extended to the Nicasio Reservoir. This could increase water supplies by 30 million gallons per day.

“This one would not be considered a staged project,” Sellier said. “Only the Nicasio segment would be considered a staged project, so you have to build the whole thing from Cotati, about 23 miles of pipe.”

The total estimated construction cost is $319.6 million. Sellier said re-routing the pipeline — running it through 12 properties instead of public rights-of-way — could reduce costs by $36 million by shortening the line by 3 miles. But that alternative would require easements, the cost of which is unknown.

“We’re not entirely sure whether this benefit we’re seeing really exists or whether it’s simply a zero-sum game,” Sellier said.

District staff is working on an assessment of PG&E’s power availability for the projects and will provide an update to the board at a future meeting.