A U.S. Environmental Protection Agency review found that despite cleanup dredging in 1996, levels of two pesticides not used in the United States since the early 1970s -- DDT and dieldrin -- are rising in fish in the Lauritzen Channel and Parr Canal, two waterways in Richmond's Inner Harbor.
Some fish tested at the site are now more contaminated than those tested before the cleanup, local officials said.
"I'm disappointed in the EPA for not doing a better job of cleaning it up," Richmond Councilman Tom Butt told the Contra Costa Times. "When you have concentrations of toxic chemicals at the level they're reporting, it's got to have an effect."
Sharon Lin of the EPA oversaw the initial cleanup in 1996.
"We thought the system would come back and the concentration levels would be safe," she said.
Instead, after dropping at first, toxicity increasing year by year and is now at levels where they were before the intervention.
"We're no longer using DDT and dieldrin, so it's sitting somewhere, contributing to contamination," Lin said.
In the 1940s, a chemical plant near the waterways processed DDT, which was banned in the United States in 1972.
The 1996 cleanup saw 107,000 tons of sediment dredged, put on rail cars and sent to a hazardous waste dump.
But the cleanup didn't capture all the chemical-laced sludge, Penny Reddy, who now manages the cleanup for the EPA, said.
"What happens over time is that with the tides coming in and out and ships coming in, it redistributes all the contaminated sediment," she said.