Cosgrove Tunnel, and is still available as standby transmission for moving water from the Wachusett Reservoir to the Carroll Water Treatment Plant. It was used for this purpose during a tunnel shutdown in 2003. The Hultman Aqueduct begins at the Carroll Water Treatment Plant and parallels the MetroWest Water Supply Tunnel (MWWST), which replaced it in 2003. After the MWWST's completion the Hultman Aqueduct underwent a major reconstruction project, which lasted from 2009 to 2014, with the goal of maintaining it as a standby alternative to the MWWST. With the completion of its refurbishment in 2014 it returned to standby status for use in the event the MWWST is unavailable. The Wachusett Aqueduct open channel extends past the Carroll Water Treatment Plant and connects the underground portion of the Wachusett Aqueduct to the Sudbury Reservoir. Before the Hultman and Cosgrove aqueducts were built this served as the primary method of transmission for water from the Wachusett Reservoir. Although no longer used for that purpose it is maintained as emergency transmission. In an emergency this can be used to feed untreated Quabbin and Wachusett Reservoir water into the emergency source reservoirs. The backup Weston Aqueduct runs from the Sudbury Reservoir in Framingham, running to the Loring Road storage tanks in Weston via the Weston Reservoir (a backup surface storage reservoir). The Hultman Aqueduct and the MWWST connect with the Sudbury Reservoir and Weston Aqueduct. The Sudbury Aqueduct runs from Foss Reservoir (Framingham Reservoir No. 3) in Framingham directly to the Chestnut Hill Reservoir, parallelling the MWWST. Sudbury Reservoir and Foss Reservoir are connected by a surface waterway. Framingham Reservoirs No. 1 and No. 2 are downstream on the Sudbury River from No. 3, and are no longer designated as emergency water supplies. Construction on a redundant barrel of the Chicopee Valley Aqueduct was substantially complete in 2008. During the failure of the interconnection between the MWWST and City Tunnel in May 2010, the MWRA drew water from the Chestnut Hill Reservoir, Spot Pond Reservoir, and Sudbury Reservoir via the Sudbury Aqueduct. The Hultman Aqueduct was unavailable as a backup as it was undergoing reconstruction at the time. In an emergency, water can be treated with sodium hypochlorite at any point in the system by deploying Mobile Disinfection Units – trailer-mounted units that the MWRA has stored at strategic locations throughout its system. Emergency chlorination was used during the main break of