Excavation work on Chestnut and Oak streets in the center of town will begin Monday as contractors replace the underground water mains from the intersection of Chestnut and School streets to Oak and Maple streets, officials said . The work will continue through August, and officials said they expect the roads will be repaved by next summer. Homes and businesses in the area will be hooked up to a temporary water main during the replacement project. The roads will remain open to vehicles, but officials warned of possible traffic backups, with limited access during work hours, and the portion of Oak Street shifted to one-way traffic for the duration of the project. For more information, visit www.needhamma.gov.