When Raychem was sold in 1999, it left behind about 40 acres of land and groundwater contaminated with industrial chemicals on its Constitution Drive campus. The next company to occupy the property in Menlo Park spent seven years scrubbing the soil until toxin levels were acceptable for commercial and industrial use, according to the state.

That's not clean enough for Facebook. According to the California Department of Toxic Substances Control (DTSC), the social networking company proposes to keep cleaning, even going so far as to have the dirty soil and the 11,400-square-foot cap installed over the contaminated area hauled away for disposed at a licensed facility. The toxins include polychlorinated biphenyls and other chemicals associated with electronics manufacturing.

"We didn't want there to be any question whatsoever about our interest in meeting the appropriate standard," said Facebook spokesman Tucker Bounds. A DTSC representative estimated that the proposed remediation will cost $5.7 million.

Once that's finished, Facebook plans to knock down the existing structures to create a 440,000-square-foot "West Campus" at 312-314 Constitution Drive that can accommodate up to 2,800 employees in five two- to four-story buildings clustered around a courtyard, according to the environmental impact report on file with Menlo Park. Groundwater monitoring and environmental site inspections by the state would continue. Employees would start moving in during 2015, according to Mr. Bounds.

The state agency expects cleanup to start in September. A community meeting will be held Wednesday, Aug. 22, at 6:30 p.m. in the Senior Center at 110 Terminal Ave. in Menlo Park. As part of the state's outreach, a fact sheet in English and Spanish was mailed to more than 600 residences in the area. The state agency also plans to contact local leaders to encourage people to comment and attend the meeting, a DTSC spokesperson said.

Public comment may be submitted until Sept. 6 to project manager Chip Gribble at CGribble@dtsc.ca.gov or 700 Heinz Avenue, Berkeley CA 94710.

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