The Palos Verdes Shelf site is an area of contaminated sediments in the Southern California Bight offshore of Los Angeles, California. These sediments were contaminated by DDTs and PCBs in wastewater discharged through ocean outfalls, off the Palos Verdes Peninsula, operated by the County Sanitation Districts of Los Angeles County. The DDTs originated from industrial wastewater discharged through sewers from the Montrose Chemical Company’s former manufacturing plant in Torrance, California. The PCBs, derived from several sources in the greater Los Angeles area, were also discharged to the sewer systems and eventually released through these same ocean outfalls.

Much of the released DDTs and PCBs settled out on the ocean floor. An estimated 110 tons of DDTs and 11 tons of PCBs were deposited in a 17 square mile area of ocean floor on the Palos Verdes Shelf in the Southern California Bight. Affected species include bald eagle, peregrine falcons, brown pelicans, a variety of sea birds, marine mammals, and fish. The U.S. Environmental Protection Agency placed the Montrose Chemical Company site in Torrance on the National Priorities List in 1989.