After a busy primary season in the 1st Congressional District, it's been a quiet summer.

That will change after Labor Day Weekend.

One of what will likely be many joint forums for Democrat Chellie Pingree and Republican Charlie Summers was announced Thursday by a group of 20 Maine nonprofits.

The groups, all of which focus in one way or another on the environment, want the candidates to talk about global warming, alternative transportation, clean energy, land protection, wildlife habitat, water quality, reducing toxins and supporting Maine agriculture and fisheries, according to the Natural Resources Council of Maine.

The forum will take place from 3-5 p.m. September 28 at the event room on the seventh floor of the Glickman Library on the University of Southern Maine's Portland campus. The public is invited to attend free of charge, but space is limited. For reservations, e-mail info@trails.org.