The $50 million plan will target a Superfund site lurking in the waters off the scenic Palos Verdes Peninsula in order to reduce concentrations of the chemicals in fish in that area.
About 110 tons of DDT from a manufacturer and 10 tons of PCBs from industrial operations flowed for years through the Los Angeles County sewer system into the ocean and accumulated in a nine-mile-long swath. Now, an existing thin layer of silt over the contaminants is showing signs of erosion.
Keith Takata, the EPA's Superfund director for the region, said the cap will be placed over the most contaminated sediment on what's known as the Palos Verdes Shelf.
The government will also continue programs aimed at educating the public to not eat contaminated fish.
EPA project manager Carmen White said the actual capping won't happen until 2012, after the best method for placing the sand is determined. The new material can't simply be dropped from the surface because that would stir up the contaminated sediment and spread it. Rather, it must be released close to the bottom, White said.
White said 800,000 cubic yards of clean sand are available from a Los Angeles harbor deepening project and sand could also be transferred from uncontaminated areas of the shelf.
The contaminated sediment cannot be dredged up because that would release some of it into the environment, she said. Using a suction system would require treatment of huge volumes of water as well as the contaminated sediment, which would take years, she said.
The DDT was released from 1947 to 1971 by manufacturer Montrose Chemical Corp. into sewers that flowed into the Pacific. Widely used until its environmental impacts were recognized, DDT was banned in 1972.
PCBs, short for polychlorinated biphenyl, were used in a wide range of products and materials including electrical equipment, oils, insulation, adhesives, plastics and floor finish, according to the EPA. PCBs were manufactured in the U.S. from 1929 until they were banned in 1979.
High levels of DDT and PCBs can move through the food chain by accumulating in microorganisms, worms, fish and birds. Human consumption can harm the liver and central nervous system and increase cancer risks.
DDT also thinned the eggshells of birds such as bald eagles, brown pelicans and peregrine falcons, preventing eggs from hatching and putting those species at risk.
The now-defunct Montrose Chemical, other chemical companies, the county sanitation district and others eventually settled lawsuits by the state and federal governments. The settlements set aside $136 million to address the contamination.