The Santa Susana Field Lab — overlooking Chatsworth, Simi Valley, and Canoga Park — was a nuclear testing site for America’s space exploration programs from 1948 until 2006. In July 1959, it suffered a partial nuclear meltdown — which was covered up — that released clouds of radiation. In the decades since, arguments have dragged on about how to clean up the contaminated site and who will pay for it. This saga is the focus of a new documentary called “In the Dark of the Valley.” KCRW talks with director Nicholas Mihm and two people in the film — Melissa Bumstead, who lives near the site, and KNBC-4’s investigative reporter Joel Grover, who’s been following the story for the last six years. Journalist Warren Olney also shares how he helped break the story of the Santa Susana meltdown decades ago.