The Callahan and Sumner Tunnels have water in the standpipe from __ each year.

The correct answer indicates that the Callahan and Sumner Tunnels have water in the standpipe from May to October each year. This timeframe aligns with the typical seasonal patterns where the presence of water is maintained for various operational and safety reasons.

In warmer months, especially during May to October, there's an increased likelihood of humidity and higher temperatures, which can lead to the need for additional water in systems designed for fire suppression and management. Additionally, maintaining water in the standpipe during this period may also coincide with increased construction and traffic activity in the tunnels, necessitating a prepared response for any potential emergencies.

Understanding operational requirements, such as maintaining water in standpipes during specific months, is crucial for fire safety management and ensures that firefighters have immediate access to the resources needed to effectively respond in emergencies.