At the request of the Massachusetts Water Resources Authority, in case of emergency shutdown of the primary water supply tunnel at the John J. Carroll Water Treatment Plant, we designed a solution for transferring water to a secondary supply tunnel. To replace the current time-consuming transfer procedure, we prepared and reviewed several scenarios, ultimately recommending and designing installation of two butterfly valves in one existing chamber a short distance upstream of the plant, saving the client more than $200,000 in construction costs compared to their preliminary design plan.