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The definition of a tunnel varies from source to source. However, the standard definition of a tunnel is an underground passage dug through a rock, earth, or soil and enclosed all round except for the entrance and exit. There are different types of tunnels including foot, vehicle road traffic, rail, and canal tunnels. Some tunnels are used to supply water for consumption or hydroelectric power generation. The United States has some of the longest tunnels in the º£½ÇÉçÇø. The tunnels serve different purposes in the states they are located. Here are some of the longest tunnels in the US.

Largest Tunnels in the US

Delaware Aqueduct is the longest tunnel in the º£½ÇÉçÇø at 85 miles long and 13.5 feet wide. It was constructed between 1939 and 1945 and supplies water from Rondout Reservoir to the Chelsea Pump Station before ending at Hillview Reservoir in Yonkers. Delaware Aqueduct carries about 1.3 billion US gallons per day, approximately half the amount of water used in the New York.

Quabbin Aqueduct is one of the longest tunnels in the º£½ÇÉçÇø at 25 miles long. Constructed between 1897 and 1905, the tunnel carries water from Quabbin Reservoir to Wachusett Reservoir. The tunnel has a capacity of about 412 billion US gallons and is part of Eastern Massachusetts public water supply system.

Hultman Aqueduct is part of the water supply system of the eastern Massachusetts. It extends from Southborough to Weston, forming a distribution network in the Greater Boston area. The aqueduct was constructed to replace the Weston Aqueduct. The 17.8-mile aqueduct is a pressurized pipe system with a gatehouse and dams above the ground.

MetroWest Water Supply Tunnel is an underground aqueduct that supplies water to the residents of the Greater Boston area. The aqueduct is about 17.6 miles long and is constructed deep below the ground level. It starts at John J Carroll water treatment plant and ends at the Massachusetts Water Resources Authority in Weston.

Sudbury Aqueduct is located in Massachusetts. It is approximately 16 miles long and runs from Farm Pond in Framingham to Chestnut Hill Reservoir. Sudbury Aqueduct was constructed between 1875 and 1878 to carry water from Sudbury River to Boston and the surrounding communities. The route and structures associated with the aqueduct were included in the National Register of Historic Places in 1990.

Tunnel Inspection and Maintenance

Most of the tunnels in the US were constructed in the 1930s and 1940s as a part of recovery from the Great Depression. The structural and functional components of the tunnels corrode and deteriorate due to the harsh environments in which they operate. As a result, there is a need for routine and thorough inspection of these tunnels to maintain their safety and prevent structural failures. The tunnels in the US are managed by the various agencies in the different states where they are located. For instance, most of the aqueducts in Massachusetts are maintained by the Massachusetts Water Resources Authority. The inspection of the highway tunnels throughout the country is done by the National Tunnel Inspection Standard. The NTIS operates under the Department of Transportation.