The Environmental Protection Agency is examining homes and schools in Sunnyvale after toxic groundwater was discovered in the area.
Tech companies Advanced Micro Devices Inc, Northrop Grumman Systems Corporation and Philips are believed to be responsible for the pollution, EPA officials said.
"Unfortunately, some of the companies are dragging their feet and the public needs to get involved to make sure they do the right thing," said Lenny Siegel, Center for Public Environmental Oversight's executive director.
The chemicals have been underground for up to 30 years, officials said. The groundwater in the affected area tested positive for a chemical compound called TCE, a solvent left behind by the electronic manufacturers.
"The risk for pregnant women is that their babies will be born with cardiac birth defects," Siegel said.
San Miguel Elementary is one of the buildings sitting on the contaminated water. The EPA said the toxins could be seeping up through the ground and then could become trapped in buildings, including schools, through a process called "vapor intrusion."
Jody Lee, who is enrolling her son John at the school, is new to the area and had no idea the campus sits on a plume of contaminated water.
"That's a little alarming," she said.
San Miguel Elementary, along with two other schools, and 100 homes are in the affected area, officials said.
A letter from the San Francisco Bay Regional Water Quality Board to the EPA warns that Philips may be endangering human health because it has not submitted an acceptable clean-up plan. Phillips officials say they have tested the area and found no risks to residents.
"The company takes the health and safety of the community very seriously and regular testing at these sites has confirmed there is no immediate risk to residents," said Lea Armstrong, Philips spokesperson.
Several residents are frustrated and said they had no idea their homes and schools could be making their families sick.
"I hope they make good on their responsibility to the state of California, to California's future and to the children and families who are here now," Lee said.
The EPA said two of the three schools in the affected area have been tested. Those tests showed normal results. However, none of the homes in the area have been tested for contamination to date.
EPA officials said more tests are planned for the fall and winter.