MMWD digests ‘breathtaking’ costs of water pipeline options

The Marin Municipal Water District’s water supply projects can’t be phased as the staff had hoped.

Staff presented an update on its pipeline projects to the operations committee at its meeting on Friday. The update included construction cost estimates on three water conveyance options, and news on how they could be built.

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

The utility is exploring whether to connect pipelines in Petaluma and Cotati to its reservoirs in order to fortify its supply. The pipelines would transport treated Russian River water into 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 decided on 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.

Originally, staff believed the project could be phased. Phase one would build a pipeline from Soulajule Reservoir to Stafford Lake, and the second phase would build the connecting pipe to the NMWD aqueduct system.

However, because of concerns about water velocity, pressure and quality, phased construction is not considered possible. Executing the two phases at the same time would cost the district around $137 million.

“It’s really not designed to support that usage,” said Paul Sellier, a Marin Municipal Water District manager. “To get a meaningful project out of this, we’re going to need to build phase one and two.”

A final phase would add a pipeline from the Soulajule Reservoir to the Nicasio Reservoir, and would cost about $31 million. To build the entire project — including pump stations, construction contracts and contingency — would be about $167.4 million. It would add 16.4 miles of pipeline.

The North Marin Water District aqueduct can support about 23 million gallons of water per day. Currently, MMWD takes 8 million gallons of water per day through the Ignacio pump station, and NMWD takes 4.5 million gallons per day.

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

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

The district is looking at two other options, but both have similar issues as the first because they would require multiple pump stations and have limited potential for construction. A preliminary power supply evaluation found the first option to be the most viable.

One alternative includes connecting pipelines to the North Marin Water District aqueduct system by adding a pipeline via San Antonio Road to the Soulajule Reservoir. Later phases would build a pipeline system from water tanks in Cotati down to Kastania Road and then connect the new Soulajule pipeline to Nicasio Reservoir. This would add 14.8 miles of pipeline, cost up to $340 million and increase supply by more than 30 million gallons per day.

Lastly, the district could build a pipeline that connects the water tanks in Sonoma County with the Soulajule Reservoir. The project would involve a new pipeline along the Highway 101 corridor through Petaluma to the reservoir. The next phase would extend it to the Nicasio Reservoir. It could increase water supply by 30 million gallons per day.

“This one would not be considered phaseable,” Sellier said. “Only that segment from Nicasio would be considered phaseable, so you’ve got to build the whole thing from Cotati, around 23 miles of pipe.”

The total estimated construction cost is $319.6 million. Sellier said realigning the pipeline — putting it through 12 properties instead of the public right of way — could reduce costs by $36 million by shortening the pipe by 3 miles. But this alternative would require easements, which carry an unknown cost.

“We’re not really sure if there’s really this benefit that we see, or if it’s just a wash,” Sellier said.

District staff are working on an evaluation of PG&E power availability for the projects and will return to the board with an update at a future meeting.