The project to retrofit the South Bay's largest reservoir has hit a major snag that will cause delays in its completion and double the projected cost.
New findings at Anderson Reservoir in Morgan Hill indicate a much more extensive retrofit is needed, delaying the project start for two years and sending costs soaring to $400 million, according to the Santa Clara Valley Water District.
A retrofit project was set to begin in 2018., but now it'll be delayed two years because of a new discovery.
"What we found recently is trace faults underneath that dam that we didn't know about when this dam was built," water district spokesman Marty Grimes said. "So now we have to consider what would happen if those faults were to rupture. Their location is right at the dam, and they could cause problems, causing ruptures or making the dam set after an earthquake."
That means a more extensive and costly process to dig out the dam and reconstruct it.
The modified project is not expected to start until 2020, meaning more than two years of the reservoir not capturing all the water it was built to hold.
At capacity, Anderson holds 89,073 acre feet of water, more than the other nine reservoirs in water district combined (1 acre-foot is about 326,000 gallons). But it hasn't been at capacity in years.
When tests in 2008 showed the dam could shift in a major earthquake, the water district reduced the amount it holds to just 66 percent of capacity.
While some are concerned about the reduced capacity wasting two years of precious rainwater, Morgan Hill resident Debbie Smallwood, who lives in the flood plain below the dam, is glad the district is faulting on the side of caution.
"I think it's better safe than sorry," she said. "I'd much rather see them do the project right. We just have to cross our fingers and hope a quake doesn't hit during that time, and we don't have a tragedy before they fix it."