A group of more than 150 volunteers recently joined forces to build the second and final phase of a new playground at Costa Park, on Walnut and Shirley avenues. The first phase was carried out Oct. 29. As was the case then, the volunteers taking part at the recent construction day on June 20 included local residents, members of The Neighborhood Developers, and representatives of JetBlue Airways and KaBOOM, a national nonprofit that works to create places for children to play. The Neighborhood Developers is a Chelsea-based community development corporation that seeks to revitalize distressed neighborhoods. The second phase was based on drawings created by local children. A ribbon-cutting ceremony was held at the conclusion of the build day, with Mayor Daniel Rizzo among those taking part.