Zusha Elinson/The Bay Citizen

Miguel Avalos has lived next to the AMCO superfund site for 26 years.

For the past three years, Manuel Pimentel and his wife and two small children lived half a block from a toxic Superfund site in West Oakland.

The site -- a gated concrete lot with the Environmental Protection Agency's yellow testing wells and a few buildings covered in graffiti -- was the old AMCO chemical distribution facility. The ground is full of cancer-causing contaminants like vinyl chloride, and the chemicals have seeped under the old row houses on Third Street.

But as Pimentel moved his family last week 13 miles away to Richmond, he said he had also worried about other sources of pollution: Interstate 880, which looms across Third Street, and the Port of Oakland with its diesel tractor trailers just beyond the highway.

“There's all this other stuff on top of the AMCO site,” said Pimentel, a jovial 30-year-old with a chin-strap beard and slicked-back hair. “It might be different if you don't have little kids, but I just decided I didn't want to take the chance that in 30 years my little girl has some kind of cancer.”

Testing by the E.P.A. has found that, in spite of the dangerous chemicals trapped under the ground, vapors from the Superfund site posed less of an immediate threat to neighbors than the air they breathe every day. A 2008 study by the California Air Resources Board showed that the cancer risk from diesel emissions was 1,500 in a million for the people living along Third Street, more than three times higher than the Bay Area average.

“The ambient air is actually worse than this thing that the government calls the worst thing possible,” said Brian Beveridge of the West Oakland Environmental Indicators Project, an environmental organization.

Pimentel used to be known as Little Wal-Mart at the flea market where he sold sunglasses, water filters, toys and Mexican food from his taco truck. He paid $1,200 a month for the apartment he shared with his wife, Lorena Mendoza, and children, Alex, 8, and Samantha, 3.

Pimentel and Greenaction, an environmental organization, tried to get the E.P.A. to help finance the family's move. They argued that the cumulative effects of the air and the Superfund site made it a dire case. But the actual science of measuring cumulative impacts is still nascent, and the E.P.A. wouldn't bite.

Pimentel, who now has a sign and decal business, dug into his savings for the new house -- and he now pays more for his mortgage than he did for rent.

His former landlord, 67-year-old Miguel Avalos, still lives upstairs from the Pimentel apartment, which is still empty. Avalos has owned and lived in the building since 1984, and he said he felt just fine.

A man of few words who speaks only in Spanish, he said matter-of-factly, “Yes, it's going to be difficult to rent this out I imagine.”

This article also appears in the Bay Area edition of the New York Times.