The Chemical Legacy of Old Silicon Valley

This map shows the sites of toxic chemical "plumes" in Santa Clara County, CA. Toxic chemicals left by old Silicon Valley companies in the 1980s still remain in the earth. Some of those chemicals are still slowly rising through the soil and groundwater via a process called vapor intrusion.

The purple shapes represent areas of vapor intrusion. An environmentally-focused technology company called Terradex has calculated the geometry of these vapor intrusion sites using government data from a number of government agencies including the California Water Resources Control Board and the Environmental Protection Agency. Click the shapes for more information and toggle the layers to see the historical locations of old Silicon Valley companies from the era that produced many of these sites.

Watch the full report by NBC Bay Area's Investigative Unit.

Map by Investigative Unit Digital Editor Scott Pham.