https://en.wikipedia.org/wiki/Gruinard_Island Somewhere I remember hearing that to make Gruinard habitable they started out by scraping 4" of topsoil off the whole thing and burning it. Fortunately smallpox ain't anthrax but bioweapons are nasty regardless.Starting in 1986 a determined effort was made to decontaminate the island, with 280 tonnes of formaldehyde solution diluted in seawater being sprayed over all 196 hectares of the island and the worst-contaminated topsoil around the dispersal site being removed. A flock of sheep was then placed on the island and remained healthy. On 24 April 1990, after 48 years of quarantine and 4 years after the solution being applied, junior defence minister Michael Neubert visited the island and announced its safety by removing the warning signs.[9] On 1 May 1990, the island was repurchased by the heirs of the original owner for the original sale price of £500.