The historical practice of ocean dumping in United States waters has been driven by both the economics of hazard disposal and a desire to place contaminants far from population centers. With the formation of the Environmental Protection Agency (EPA) in 1970 and a growing body of science that revealed the negative impacts of dumping to the environment, the process became federally regulated with strict guidelines and a permit approval process when the 1972 Marine Protection, Research, and Sanctuaries Act was passed by Congress (MPRSA (1)). Twenty-six years later, an outright ban of industrial waste dumping was enacted through the Ocean Dumping Ban Act of 1998 (Public Law 100-688), with remaining permitted dumping activities limited to sewage and dredge spoil disposal. Prior to legal protection, the ocean was a favored disposal site for industrial waste, with 23 known sites used offshore the Atlantic, Gulf, and Pacific Coasts. (2) Disposal took the form of both containerized waste and bulk dumping. (3)

Southern California’s coastal ocean hosts productive fisheries, is home to now protected ecosystems, and has an established tourism industry that is based on coastal recreation. Dump sites offshore California were established as early as the 1930s, became regulated in 1961, and were used for a variety of industrial purposes including disposal of waste from oil and gas production and the chemical manufacturing industry. Concern over these historical practices and their impact on the environment were described to the California Regional Water Quality Board in 1985. (5) The report documented extensive regulated dumping of a variety of bulk and containerized materials and the possibility of short-dumping, disposal prior to reaching the sanctioned dumping location. The San Pedro Basin, located in Southern California waters between Santa Catalina Island and Palos Verdes Peninsula at depths ranging from 600 to 900 m, was a dump site for military munitions (6) and a range of industrial wastes, including waste from refineries and chemical production. This included waste byproduct containing the pesticide dichlorodiphenyltrichloroethane (DDT), generated by the Montrose Chemical Corporation. Between 1947 and 1961, up to 700 t of DDT contained within acid sludge were dumped. (5) While only accounting for a small fraction of the total overall waste recorded as dumped, the DDT waste byproducts are of particular concern due to the long life of the chemical. DDT is now well understood to be both toxic and stable with long-lasting negative environmental impacts (7) including contamination of food webs, altering reproduction cycles, and contributing to cancer within wildlife. (8,9) As an endocrine disrupter and immune suppressor, recent studies have demonstrated human health linkages between DDT exposure from fish consumption and breast cancer in women that can be passed down through generations. (10) Interest is growing to develop a long-term strategy to assess the risk this dump site poses for both the surrounding marine ecosystem (11) and the coastal population of Southern California. To date, no systematic survey of the locations and conditions of the dump site has been conducted, due in part to the historical technical challenges associated with deep water survey. Although the presence of DDT in seafloor sediment samples has been recognized for decades, (12,13) it was only recently that surveys investigated whether barrels found on the seafloor could be a source. (14) Several studies have been published documenting the negative impacts of DDT to the marine food web in Southern California including birds, (15) dolphins, (9) and humans. (16)...