Tenders have been returned for the £50 million clean-up of the former Avenue Coking Works in Chesterfield for the East Midlands Development Agency. The Derbyshire complex is one of Eu rope's most polluted sites. Balfour Beatty, Costain, Kier, Mowlem, Morgan Est, Nuttall and Dredging Environmental Contracts ? part of Belgian firm Dredging International ? will find out in December which has won.