PORTLAND, Ore. (AP) - A chemical stew oozing through groundwater into the Willamette River has forced the U.S. Environmental Protection Agency to take over Superfund cleanup planning from the company responsible for the pollution.

A manufacturer now called Arkema Inc. dumped, piped and leaked poisonous DDT, rocket propellant, ammonia, hydrochloric acid and other chemicals on its grounds over the past 60 years to create what federal officials call the most contaminated site in the Superfund project.

The EPA, which is dealing with dozens of companies along the six-mile long Portland harbor cleanup site, says the company is a year behind schedule while contaminants have continued to pour into the river. Planning is so involved and contentious that Arkema won't likely complete an initial cleanup until 2010.

"To be this incomplete this late in the game just looks as if they're not cooperating," said Sean Sheldrake, EPA's project manager for the Portland harbor. "The pace here isn't keeping track with the urgency."

Arkema officials say they are cooperating.  Doug Loutzenhiser, executive vice president of Legacy Site Services, an arm of Arkema's former parent company, says the biggest hurdle to an agreement is defining the size of Arkema's portion of the cleanup. Arkema is suggesting about 11 acres. But the EPA contends the company's planning work is so inadequate the agency cannot begin defining an area considered so toxic that it must be isolated and addressed before broader plans can proceed.

The EPA suggests that much of the river's DDT - the pesticide banned 10 years after Rachel Carson's 1962 book "Silent Spring" asserted that it moved up the food chain to ultimately poison humans - can be traced back to Arkema.  The site encompasses 54 flat acres in the heavily industrialized riverfront east of U.S. 30, across the river from the University of Portland. All that remains of structures there is a 1940s administration office, and beyond it, crumbling concrete foundations and pitted asphalt littered with freshwater clamshells dropped by birds.

From 1941 until the plant closed in 2001, up to several hundred people made industrial chemicals around the clock. They shot saltwater through electrolytic cells to produce sodium chlorate, an herbicide and bleach for paper pulp. They also made chlorine, caustic soda and hydrochloric acid. Over the years, they also produced DDT, ammonia and rocket propellant. Between 1947 and 1954, DDT manufacturing led to contamination of the ground and river. According to environmental records, workers dumped DDT residue into a floor drain piped to the river. The flow was eventually redirected to a nearby pond and, later, to a 285-foot-long trench.

Asbestos, used in the electrolytic cells, was routinely buried in trenches until 1990, reports show. The company removed the asbestos two years later under a plan to redevelop the land.  Loutzenhiser said the company has already spent "millions" cleaning up the site, including removing 6,400 tons of soil and paving the area over an old DDT pond to keep rainwater from flowing through contaminated soil and into the river.

But Travis Williams, a member of a Portland harbor advisory group and executive director of watchdog group Willamette Riverkeeper, praised EPA's demand for more data and takeover of the work plan, especially because of DDT's threat to wildlife and humans.

"Given the stakes here, we absolutely need to have a full understanding of the fate and transport of this material," Williams said.