Tunnel project yields a lot less water than hoped for

CORRECTION: The County Times article, and an earlier version of this story described the Tunnel site as Montara Mountain. It’s actually San Pedro Mountain.

The Devil’s Slide Tunnel project has uncovered a lot less water than expected, dashing hopes for the time being that it would be able to increase the water supply in Montara and Moss Beach, reports Julia Scott in the County Times.

According to a recent assessment by Devil’s Slide tunnel project manager Skip Sowko, the largest volume of water discovered so far at about a quarter of the way into the tunnels is 7.92 gallons per minute (or 30 liters per minute). A typical person in the shower uses six gallons of water per minute.

"It’s a pleasant surprise because it would be difficult for us if it were on the higher end," Sowko said.

The state Department of Transportation pumps all the water it finds into storage tanks. The silt and clay must be removed before the water is discharged into the ocean.

It is still possible, and even likely, that work crews will discover a higher volume of water as they bore northward through the mountain toward Pacifica, where less-pervious rock surfaces may spill more water when cracked open, according to Sowko.

The North Coast County Water District, serving Pacifica, has jurisdiction over roughly two-thirds of Montara Mountain, and therefore two-thirds of its water. At 1,000 feet in, the boring machines have already left Montara’s territory.