FL: residential limit for arsenic in soil or fill is 2.1 milligrams per kilogram

"...But the lake's shrinkage has also left a monumental cleanup headache: a bathtub ring of toxic sludge from dumped wastewater and the objects hurled in by hurricanes and litterbugs. The slimy gray lining, if not a silver one, is that the drought has given water managers an opportunity to scoop out the muck and refresh the shoreline habitat for Okeechobee's flora and fauna. In little more than two months, contractors with the South Florida Water Management District have hauled away 2 million cubic yards of sludge — enough to fill nine football stadiums from the field to the nosebleed seats, said Tom Debold, water district supervisor on the muck-removal project. After the muck was scraped and temporarily stored in 20-foot-high mounds set back from the shore, scientists discovered that much of it contains excessive levels of arsenic from pesticides and fertilizers used until the 1960s. Water district and Army Corps of Engineers officials who maintain much of the lake's surrounding levee and its intricate network of canals, sluices and pumps had hoped to sell the excavated sludge to builders for landfill. But after analysis, they concluded that "it can't be used near any kind of housing facility," said Susan Gray, a biologist and deputy director of watershed management for the district. The residential limit for arsenic in soil or fill is 2.1 milligrams per kilogram; the Okeechobee muck had as much as 9 milligrams per kilogram, Gray said. The concentration of arsenic, which cannot be treated or neutralized, is intensifying as water evaporates from the sludge and the desiccated piles compress. Removal of the muck has allowed fresh shoots of bulrush and tape grass to sprout and will improve the habitat for the bass and crappie that draw thousands of anglers to the lake each year.... --http://www.latimes.com/news/nationworld/nation/la-na-lake19jul19,1,1305309.story?coll=la-headlines-nation from: Okeechobee's treasures and toxic muck Archeologists gather clues to South Florida history as water managers work to clean up the sludge left by drought. By Carol J. Williams, Times Staff Writer July 19, 2007