Santa Clara County dam faces growing opposition

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The opposition against the Pacheco Dam expansion in South County is growing—and so is the list of plaintiffs suing Valley Water over the project.

This week, the environmental advocacy group Sierra Club and the Amah Mutsun Tribal Band have added their names to the Stop Pacheco Dam Coalition, which is suing Valley Water. The lawsuit, first filed in June by environmentalists and landowners, challenges the water district’s reliance on environmental exemptions, arguing it will result in grave environmental consequences.

“Valley Water is cutting corners on the environmental review for these investigations and acting like they have no impact when in fact, they do. They would require mitigation and avoidance measures if you were to carry them out,” Osha Meserve, a Sacramento attorney representing the dam opponents, told “This is a very wild and sensitive area, so running around with a bunch of trucks and helicopters and digging holes does have impacts.”

Valley Water wants to repair and expand the size of the Pacheco reservoir and dam atop the remote Pacheco Pass in Santa Clara County from 5,500-acre feet of water to 140,000-acre feet of water. This would be roughly 25 times the original size and could flood up to 1,500 acres. It’s a massive undertaking that would cost $2.5 billion and take a decade to complete. Right now, the water district is determining the best way to engineer the dam.

Geological work includes drilling 226 borings and digging 57 test pits up to 20 feet deep over the next eight to 17 months on various properties, including several private ranches that would be flooded by the dam, according to the lawsuit. Trucks, trailers, heavy equipment and helicopters would traverse the Diablo mountain range—an area plaintiffs say is rich in biodiversity and cultural resources. The coalition also claims Valley Water could take private property through eminent domain.

Valley Water officials say their plan is within the law and necessary as the county endures another drought. The new dam will hold enough water to supply 1.4 million residents for a year in an emergency. The existing dam, built in 1939, was listed as “high hazard” in 2019, meaning it could break and have catastrophic impacts in the area. Valley Water emptied the reservoir, but instead of repairing the dam, they want to expand it.

Weathering droughts

Officials say the expansion will reduce the frequency and severity of water shortages during droughts because it could capture and store more water during wet years. They also say a larger dam will protect the drinking water supply and infrastructure and improve fish habitats.

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“Valley Water is exploring ways to secure enough water to help our communities weather future droughts. These efforts include increasing Santa Clara County’s use of purified water and evaluating a variety of water storage projects, including the Pacheco Reservoir Expansion Project,” spokesperson Matt Keller told “Valley Water has complied with all environmental requirements for this work and will continue to do so for the length of this project.”

But plaintiffs argue the water district is skirting the 1970 California Environmental Quality Act (CEQA) that requires detailed studies of major construction projects.

The water district is doing the investigative geological work without an environmental impact review or CEQA because Valley Water officials say the drilling and digging will not have significant impacts on the land. Under state law, CEQA is not required if there is minimal impact.

Because Valley Water is the lead agency on the dam project, it can create its own environmental impact review. Last year, the California Water Commission voted to grant the project nearly half a billion dollars because it published a draft of the environmental impact review and secured other sources of funding by Dec. 31. So far, the water district has $506.6 million secured—a fifth of the project’s total cost. None of the dollars are from the federal government.

But the Stop Pacheco Dam Coalitions says the investigation will undoubtedly have environmental consequences.

Environmental, tribal impacts

The dam site is fairly secluded, with little to no roads. There are several threatened and endangered species that would be harmed by the geological work, said Katja Irvin, who leads the water committee of the local Sierra Club chapter. This includes California red-legged frogs, the California tiger salamander and special status plant species like the Lemmon’s jewelflower and Arburua Ranch jewelflower.

“The California red-legged frog is one of the most sensitive species in the area that may be impacted,” Irvin told “The movement of equipment will involve crossing streams which could directly impact frogs and frog habitat at the crossing locations.”

Irvin said it could also impact water quality downstream by releasing sediment and introducing toxic materials. Runoff from these locations could also impact streams and seasonal wetlands in the areas that serve as frog habitats.

Valentin Lopez, tribal chair of the Amah Mutsun, said in addition to the environmental impacts, the Pacheco Dam project will damage the indigenous population’s cultural sites including its burial grounds.

“It’s important that our tribe opposes the dam and protect and preserve the resources and the burial grounds of our ancestors,” Lopez told “We recognize the intent of the dam is to provide water, but there are alternatives and rules the (water district) is not considering.”

The lawsuit is part of a bigger opposition against the dam. The coalition believes the project poses too great a risk financially, without solving Silicon Valley’s water challenges.

“We think the dam project would be terrible for the environment, terrible for ratepayers and not help with water supplies that Valley Water says it needs. That’s our bigger target,” Meserve said. “But we think the investigation part is an important step along that pathway. We’re trying to force Valley Water to do it correctly if they’re going to do it at all.”

Contact Jana Kadah at [email protected] or @Jana_Kadah on Twitter.

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