The contractor overseeing the demolition of buildings on the Starmet/Nuclear Metals hazardous waste site in West Concord began preparation work last week. The work included clearing trees near the buildings and minor earth work to prepare staging areas for trucks. US Environmental Protection Agency officials have said the cleanup and demolition will take about three years. In 2001, the property at 2229 Main St. was added to the Superfund National Priority List, which includes the country’s most serious hazardous-waste sites identified for possible long-term cleanup. According to the EPA, various owners and operators used the Concord site for research and specialized metals manufacturing, and were licensed to possess low-level radioactive substances.