LOS ANGELES (CBS News) — Just 10 miles off the coast of Los Angeles lurks an environmental disaster over 70 years in the making, which few have ever heard about. That is, until now, thanks to the research of a University of California marine scientist named David Valentine.

Working with little more than rumors and a hunch, curiosity guided him 3,000 feet below the ocean’s surface. A few hours of research time and an autonomous robotic submersible unearthed what had been hidden since the 1940s: countless barrels of toxic waste, laced with DDT, littering the ocean floor in between Long Beach and Catalina Island.

But this offshore dump site is only a part of the story of environmental damage from years of DDT discharge along the coast of Southern California — a story which likely won’t be closed for decades to come because of its ongoing impact, including a recently discovered alarming and unprecedented rate of cancer in the state’s sea lion population, with 1 in every 4 adult sea lions plagued with the disease.

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