President Donald Trump will nominate a seasoned environmental lawyer to head what has become one of the most difficult jobs to fill at the Environmental Protection Agency.

Alexandra Dapolito Dunn, currently the administrator of EPA’s Region 1 office in Boston, will be named assistant administrator of the EPA for Toxic Substances, the White House announced Aug. 31.

Before her appointment to the EPA’s New England region, which covers Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont, Dunn served nearly four years as executive director and general counsel of the Environmental Council of the States