Charlie BreitroseMembers of the construction team working on the Lowell School renovation project look up at the school during the groundbreaking ceremony. City Council President Mark Siders had a big grin on his face as he held up three fingers and donned a construction helmet. On Wednesday afternoon, he and others involved with the Watertown Public Schools’ building projects gathered for the official groundbreaking at Lowell Elementary School’s renovations and expansion — the district’s third elementary school project in recent years. The site work had already commenced at the school that overlooks Orchard Street. Like the other two elementary school projects, Lowell was designed by Ai3 Architects and the project management firm is Hill International.