The head of the U.S. EPA’s New England office has accused New Hampshire of failing to prepare for the environmental impact of the rapid population boom that is expected to follow the widening of Interstate 93, the main commuter highway connecting the state to Boston, Mass. New Hampshire plans to spend $18 million to ease the environmental impacts of the highway project, but Robert Varney said that’s far too little to address a likely population boom in more than 20 New Hampshire communities that would tax existing services and threaten open spaces, drinking water supplies, and wildlife. Varney called for a total of $52 million to be allocated to environmental protections and he threatened delays in the highway project if the environmental concerns weren’t adequately addressed. The state is counting on federal highway dollars to cover some 80 percent of the cost of the $350 million project — meaning the EPA has significant say in the highway’s future.