ACTON, MASS. — Atlantic Management has completed the disposition of Powder Mill Plaza, a retail property located in Acton. Medipower acquired the shopping center for $16.3 million. Stop & Shop, Rite Aid, Anytime Fitness, DCU, Papa Gino’s and Dunkin’ Donuts, among other national retailers, occupy the 74,876-square-foot property. Geoffrey Millerd, Justin Smith, Paul Penman and Christopher Peterson of Newmark Knight Frank represented the seller in the deal.