http://www.miamiherald.com/static/media/projects/the-land-beneath-the-parks
Dumping grounds for waste and incinerator ash around Miami were covered over with parks and playgrounds. Methane, arsenic, benzo(a)pyrene, and other hazardous chemicals have been found in the soil under the playgrounds and in the groundwater. This has cost the municipal governments millions of dollars in soil remediation. The Miami Herald, Andres Viglucci, 2013