Silicon Valley is an economic engine with a long history of technical innovation. But there’s a dark side to that legacy in the form of hundreds of old chemical spill sites that still contain toxic chemicals. Some of these spills are from fuel leaks or dry cleaning shops but many have their origins in the early days of Silicon Valley: the 1960s and 1970s when a booming computer chip industry gave the region its name.

“The dark side of the legacy is the stuff left behind,” said Amanda “Mandy” Hawes, a worker’s rights attorney in Silicon Valley.

Hawes’ clients handled some of that “stuff” in factories and microchip clean rooms around the Bay. At the time, it wasn’t widely known just how toxic the chemicals they handled were.

“I think it wasn’t unheard of for stuff to be literally poured out the back door,” said Hawes.

Worker's rights attorney Amanda Hawes speaks with reporter Stephen Stock.

Nobody at the time knew the full implications of what they were doing.

“We only later realized that these things are actually pretty toxic,” said Stephen Hill, toxic cleanup division chief for the San Francisco bay region of California’s regional Water Quality Control Board.

“These are basically unauthorized discharges from usually many years ago,” he said. “People doing things that at the time were considered normal and industry practice, but we now know cause problems.”

The EPA recognizes 23 official federal Superfund sites with discharges in them. The “Middlefied-Ellis-Whisman Study Area” is a large, well-known Superfund site in Santa Clara County. But state and federal officials tell us hundreds of other sites are also scattered all over Silicon Valley.

“With materials that get left in place after somebody’s business moves on,” said Hawes. “Materials can end up in the water and therefore can be a problem in water quality. Some of them also have the capacity to come back up. They can become vapor again. And unfortunately we’re seeing that as well."

When the chemicals rise through the soil and groundwater they become what’s known as “vapor plumes.” NBC Bay Area has plotted the locations of these plumes along with the historical sites of old tech companies in an interactive map. Government officials have recorded more than 518 toxic plumes in Santa Clara County alone.

“It’s part of our history that shouldn’t be swept under the rug,” said Bob Wenzlau, a Silicon Valley entrepreneur. Wenzlau gathered data on toxic plumes from scattered government sources and shared some of it with NBC Bay Area. The Stanford-trained civil engineer founded a technology company called Terradex to track, monitor and educate companies, governments and citizens about contaminated sites.

“It is a bit of the dark side of Silicon Valley,” said Wenzlau. “But for me it is also an opportunity for Silicon Valley to make good.”

Wenzlau’s colleague Lenny Siegel, executive director of the Mountain View-based Center for Public Environmental Oversight, said that there’s a lack of organization and accountability on the side of government regulators.

“Part of the problem, our government is so split up into agencies and jurisdictions that there’s nobody who has responsibility for all of these sites.”

Siegel worked closely with Wenzlau on mapping all the toxic chemical spill sites and environmental restrictions they could find. Much of the data comes from the California State Water Resources Control board, but in order to get a comprehensive picture, they had to combine that information with data from other government agencies like the Environmental Protection Agency.

The end-product is “WhatsDown”, a web application that aims to show the environmental dangers that are hidden under our feet.

“What’s important is the combination of the map, and the fact that there are tens of thousands of people living and working above plumes, or going to school above plumes,” said Siegel.

Using Terradex's data, along with the original government sources, we mapped these toxic sites ourselves.

“We can actually see how much of the valley has actually been impacted by these chemicals,” said Wenzlau.

Using these tools, it’s easy to spot more than a dozen day cares, elderly care homes and schools right on top or very close to sites where industrial chemicals still lurk in the soil.

“People should be asking questions,” said Siegel. “Now, some people say, ‘I don’t want to know about it, because it’s going to lower my property values’ and, I’m sympathetic but I don’t want to be the person who buys that property not knowing.”

Vanessa de la Piedra, with the Santa Clara Valley Water District, acknowledged that the number of spill sites is surprising.

“I think most people don’t realize just the sheer number of open cases out there,” said de la Piedra. She says, however, that the spills are not an immediate hazard to water quality.

“From an environmental perspective, of course we want to see these sites cleaned up and we do want to make sure that that contamination is contained and stable. So that it doesn’t impact other properties or deeper drinking water aquifers. But you shouldn’t be concerned about your drinking water quality,” she said.

Stephen Hill, with the Water Quality Control Board, echoed de la Piedra’s confidence. “I think that the regulatory agencies are doing their job,” he said.

However, it’s clear that Silicon Valley will continue to live with the legacy of these spill sites for a very long time.

“It’s going to be years, decades perhaps,” said Hill. “There’s no current exposure, but you’re trying to clean this up because we want this groundwater to be available for future users.

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