Between the years 1875 and 1881 a tunnel, 12′ in diameter 7 miles long was constructed between a dam on the Gunpowder River and a man-made lake at Montebello. This was all part of the new, permanent water supply for Baltimore. It would eventually replace the supply from the Jones Falls. As needed, this tunnel was inspected and found to be in very good condition over the years. The majority of the tunnel is through solid rock with only a few sections having a brick lining. As the City grew, a new dam was built upstream in 1914, with a connection to the 1881 conduit.
In 1933 the City was contemplating a new source of water. The decision was made to build a parallel tunnel from Loch Raven (on the Gunpowder Falls). An inspection by the consultants was made of the old tunnel first. The below photographs show what they found – rock falls and leakage.
The old tunnel was taken out of service and the new tunnel was used. In the 50s and 60s it was decided to re-use the old tunnel, which carried raw water, to start sending processed water to Baltimore County. An inspection of the tunnel, which at this point being only 5-1/2 miles long (Bulkheads built on each end of the tunnel that were no longer needed) was done in 1968. These consultants, pictured below, found more of the same. Rock falls and leaks. 
Three of these men I eventually worked with in 1981.
Another inspection was done in 1984. Unfortunately I can not find any photographs. I do have the reports from this inspection and it is not good. More rock falls and leakage. I was asked last year to be a part of a new inspection group to enter this tunnel. I immediately said yes! BUT, over the course of a couple months preparing for this and all the safety people you can imagine being involved, it was decided to send in a remote operated vehicle. Not sure when they will do this, I just know the sub isn’t big enough for me to fit into!
Two quotes came to mind when i was asked “Why do you want to go in there? It is dangerous!”
Valeria to Conan the Barbarian – “Do you want to live forever?” And Lenny and Ziggy singing “Death by Misadventure!”
