MARBLEHEAD – The Board of Health’s state-mandated plans to cap the former town landfill and build a new transfer station off Woodfin Terrace could cost the town more than double the $11 million board members estimated in 2007.Director of Public Health Wayne Attridge, who will continue to review costs as the May 3 Town Meeting approaches, told the Finance Committee Monday evening the cost of Article 20, the landfill cap and the new transfer station, is estimated at $22.28 million. Attridge also said the cost of Article 21, the remediation of about 13 acres of Steer Swamp and Green Street and Stony Brook Road property affected by the former unregulated landfill, is estimated at $821,561.The remediation includes $380,510 set aside for the purchase of a privately owned parcel of land off Green Street, where metallic substances have been found in wetlands.The excavation and construction are scheduled to take place from August 2011 through August 2013 if the voters approve the project at Town Meeting in May and a debt exclusion override in June.Attridge pointed out that the Department of Environmental Protection has required the town to do more work since the designs began, especially where the clean-up plan is concerned. He held out the hope that the current economic situation might result in lower bids.There is another consideration involving convenience to the community.”The prices reflect (the board’s intention) to keep the area open during construction,” Attridge admitted, calling that plan “challenging” because the work area is limited.He said plans are under way to cut back the size of the transfer station building and reconfigure some areas to reduce costs.The Board of Health plans to maintain its current schedule of meetings with neighbors of the project, to address their concerns about the height of the transfer station and other issues.The board will also continue to assess private property assessments and meet with the Planning Board, Conservation Commission and Board of Appeals.”Once all the technical and legal issues are resolved, the board has a group of people who are anxious to serve on a building oversight committee,” Attridge said.