Only two species of Boreidae occur in the east (Boreus brumalis and nivoriundus) and both are found in Massachusetts. This one looks like brumalis: legs all black; abdomen shiny blackish-green with light brown lateral stripe; ovipositor shiny black [whereas in nivoriundus, legs yellow or brown with black ring at joints; abdomen black or brown, with terminal segment brown or cinnamon; ovipositor brown or reddish with black tip].
See description of both species on nivoriundus page, and compare image of female by Tony Thomas.