at Great Kills Park, part of Gateway National Recreation Area. Much of Great Kills is former marshland that was turned into recreational parkland with the addition of 15 million cubic yards of fill in the 1940s. (Compare aerial views from 1924 and 1996 to see the area's radical transformation. The peninsular part of the park was created separately, from dredged sand.) Over the past decade, much of the fill, which contained medical and sanitary waste, has been discovered to be radioactive. About half of the park is now closed off as a result (map), and a lengthy cleanup will be required before it can be opened to the public again.