Gregg served as an officer in the US Army for twenty-five years and subsequently worked as a defense industry consultant with Cypress International in Alexandria, VA. He earned his Master Naturalist Volunteer qualification from Audubon Naturalist Society in 2016 and serves as a macroinvertebrate docent for Robinson Nature Center in Columbia, MD. At the Observatory’s Southeastern Wisconsin Conservation Summit in 2019, Petersen presented colorful posters that environmental educators can use when teaching students how to measure watershed quality.