MARBLEHEAD – Bales of hay and straw stacked at the gated entrance to the long-vacant Chadwick Mills site on Lafayette Street Monday told the story: Boston Environmental, the company hired by NL Industries for the site contamination clean-up, has begun work.The harborside property on the Salem-Marblehead line, contaminated by lead and other chemicals during decades of industrial use, is eventually scheduled to become a multi-family residential property.First the contaminants must be removed.Marblehead Conservation Commission Chairman Walter Haug said the schedule was firmed up at a meeting between Boston Environmental representatives and Salem and Marblehead officials last week.The straw and the hay were for a silt fence to protect the beach area from erosion, a company representative at the site said Monday. Members of the two Conservation Commissions were scheduled to inspect that work today.If that inspection is favorable the company will begin the clean-up of the beach and harbor area. That part of the project includes closing the walking and bike trail through the property Monday, Nov. 29 and construction of a ramp across the bike path to protect the town?s electrical conduits from damage.The beach area work is expected to be done by Dec. 31 to avoid affecting the growth of eel grass. The project then shifts to the soil on the Lafayette Street side of the bike path.Vine Associates Inc. of Newburyport has been hired as a technical consultant, at a cost of $8,000.Town Administrator Tony Sasso told selectmen last week that the bike trail is scheduled to be closed until May. Signs will be posted on Lafayette Street and West Shore Drive notifying residents. Gates will also be installed prohibiting access to the path.The updated construction timeline will be posted on the town?s Web site, www.marblehead.org.Haug warned that all trees, shrubs and other vegetation in the clean-up area will be removed.?It?s going to look like bare bones and it will probably cause a lot of consternation,” Haug said, “but we?ll have to cross that bridge when we come to it.”