MOUNTAIN VIEW (CBS SF) — One of Silicon Valley’s dirty secrets is coming back to haunt Google with toxic vapors.

TCE, or trichloroethylene vapors were detected at the company’s offices in Mountain View.

READ MORE: UPDATE: Atmospheric River Crashes Onshore; Flood Warning Issued For Napa, Sonoma Counties

Google’s buildings QD6, and QD7, which sit on North Whisman road sit on top of what used to be Fairchild Semiconductor, Intel, Raytheon, and other computer chip makers.

The problem began when those chip makers dumped thousands of gallons of the toxic solvent into the ground, contaminating the water.

When Google moved in, they installed state of the art filters, and conducted rigorous air quality testing.

READ MORE: UPDATE: Streets Flood in San Rafael, Mill Valley as Wild Storm Lashes Bay Area

The EPA’s screening level for commercial buildings is 5 micrograms per cubic meter.

Most of Google’s air sample stations in the two buildings detected TCE levels below 5 micrograms per cubic meter. But about a dozen stations reported readings from 5 to 30 micrograms per cubic meter. One station reported 120 micrograms per cubic meter. Air samples are collected over 8 to 10 hour span.

Google notified the EPA of the elevated levels in late 2012. The company took several weeks to address the problem, and bring the TCE levels down. The company claimed employees had minimal exposure to the toxic vapor, given the quick response, and Google employees’ work patterns that reduce their time inside the building.

It takes decades of TCE exposure at elevated levels to cause medical problems, according to the EPA.

Google released a statement, saying “The health and safety of our employees is Google’s number one priority, and we take several proactive measures to ensure the healthiest indoor air environments possible.”

MORE NEWS: Stephen Curry Reaches 5,000 Assists, Warriors Beat Kings 119-107

(Copyright 2013 by CBS San Francisco. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)