A Weston cop was arrested by fellow cops from his own department after he plowed into a car in the police station’s parking lot and drove off, prosecutors said.Leo Richards, 54, of Weston pleaded not guilty in Waltham District Court to drunken driving and improper storage of a firearm, prosecutors said.“Richards has been placed on administrative leave from the Weston Police Department and has surrendered his badge, firearm and license to carry to Weston Police,” Middlesex District Attorney Marian T.