As the statewide drought continues, the Coastside County Water District is exploring how to maximize its local sources and not be solely reliant on imported water. Last week the district received a presentation from hydrogeologist Robert Shultz, of Geo Blue Consulting, who referenced studies of local watersheds dating back decades and made recommendations to the board.

As a result, the district is expected to pursue a pilot well and streamflow surveys for the Lower Pilarcitos Groundwater project, consider replacing wells in Upper Pilarcitos Canyon and improve production at the Denniston Creek well fields.

“This is what we’re charged to do,” Commissioner Chris Mickelsen said. “These droughts are not going to go away. We need to look locally and put more water into our system as soon as possible.”

The district relies on two imported sources and two local sources for its water. Pilarcitos Lake and Upper Crystal Springs Reservoir are operated by the San Francisco Public Utilities Commission and account for 72 percent of the CCWD’s supply. The district operates wells and surface water from Pilarcitos and Denniston creeks that make up the remaining 28 percent.

But those watersheds are a limited resource because the district can’t draw from them in the drier summer months. Cathleen Brennan, a resource analyst with the district, said the storm two weekends ago increased water flows in both creeks, and CCWD planned to start drawing from Upper Pilarcitos Creek Canyon on Nov. 1.

“We are hoping that the storm door remains open and we will be able to continue to use these local water sources throughout the winter months,” Brennan said.

Shultz noted that the Coastside has a diversified water portfolio in that there is surface and groundwater available. However, the limited surface water storage made the area susceptible to drought, and there are relatively small groundwater basins along the coastal terrace. Shultz said the past studies showed that Denniston well fields had untapped water with minimal saltwater intrusion and favorable geology of alluvium deposits, materials like clay, silt, sand, or gravel that easily transmit water.

“We need to understand the geology in order to understand the availability of water,” Shultz said.

Though Denniston is the second-largest watershed within the district behind Pilarcitos, its surface water diversion accounted for 78 million gallons, nearly 12 percent of the district’s total supply for 2021, most of which came in the months of December through April. CCWD General Manager Mary Rogren noted the district’s rights to Denniston Creek are secondary to Cabrillo Farms. Depending on yearly rainfall levels, Denniston can supply nearly 200 million gallons as it did in 2020, about 35 percent of the district’s supply. In 2019, Denniston accounted for about 27 percent.

“In 2020, I estimated it saved us about $1 million in SFPUC water,” Rogren said. By comparison, Crystal Springs Reservoir and Pilarcitos Lake accounted for 79 percent of the supply in 2021.

Shultz said the Denniston wells, most of which were installed in the 1970s and 1980s, have exceeded their life expectancy and should be replaced.

Contrary to what the name might suggest, the well fields in Pilarcitos Canyon are for surface water, not groundwater. Brennan said the district can only pump from Pilarcitos Creek from November through March each year. The wells accounted for 7 percent of the district’s supply in 2021.

For groundwater from the creek, the estimated $3.1 million to upgrade Lower Pilarcitos with a pilot well, pumping tests and streamflow survey is based on a 2003 study. The engineers estimated that the wells could supply 129 million to 259 million gallons per year during normal and dry years. Shultz explained that in general across the state, groundwater is typically the cheapest option for water districts looking for additional sources.

“If it’s available without adverse impacts to the environment and other users and if the water quality is sufficient, it’s far and away the lowest cost alternative,” Shultz said.

Another ongoing alternative discussed was the Denniston-San Vicente surface water diversion project, which the district has been studying since 1969. The plan involves diverting water from San Vicente Creek and piping it to Denniston’s treatment plant for distribution. Shultz estimated this could supply 472 million gallons in a normal rainfall year. However, the project has a broad timeline and could take years to develop. The process has dragged on because of the extensive permits required from California Fish and Wildlife Department and Golden Gate National Recreation Area, said David Dickson, CCWD’s former general manager.

“Time frames are difficult, but the good news is that they shouldn’t affect our ability to continue to divert the maximum possible amount out of Denniston,” Dickson said.

The board also discussed the possibility of adding recycled water to the system. The estimated yield would be 359 million gallons a year during a normal rainfall year. Though it comes with a steeper price tag — Shultz said the estimated cost is $10 million — experts say a recycled alternative is a reliable option during droughts.

Shultz recommended the board not pursue efforts to take water from Nuff Creek because of the ongoing mining operations at a nearby quarry and that the cost likely would outweigh the limited water supply. Shultz said it’s unknown how much water could be diverted into the future mining pit that’s expected to contain 26 million gallons within 80 acre feet, a drop in the bucket for the district’s total supply.

CCWD Vice President Bob Feldman stressed the importance of getting the district to look hard at projects it could do in the short term such as well replacements.

“Recycled water is great, but we won’t achieve that in the next five or eight years,” he said.

August Howell is a staff writer for the Review covering city government and public safety. Previously, he was the Review’s community, arts and sports reporter. He studied journalism at the University of Oregon.

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