I checked with the City Engineer about the tunnels and the reason the house was taken off the market the end of March 2013, the flooding and burst pipe, and he also had heard of the rumored tunnels but had no drawings or any proof of such.  He doubted they still exist, if they ever did, due to all the utility construction over the past 125+ years.  Regardless he did not think they would add to any flooding issues.   

     In regards to the flooding he also had not heard of any recent flooding issues.  There are combined storm/sewer lines in that area but he said it would take a monumental rain to cause any backup issues. These storm/sewer lines are NOT made for travel.  Also, the downtown is protected from the river by levees built after the great flooding of 1913.  He assured me that any downtown flooding would be something of a very rare event indeed.
     If you are an elite member of society, as Paul Sorg was, I highly doubt you would travel underground. Even if entertaining, Paul would be proud to show off his city. He would travel above ground. Paul also died before completion of the renovations of the Mansion in 1902, and Jennie barely used the house and chose to use her son Paul J Sorgs house when she was in town.  If said tunnels exist how would you get the horse and carriage above and below ground once you get home, to the bank, to the opera house? It is highly unlikely that such folklore is evident.
     I have been in the house after it went up for sale, I spent time in the basement and no where did the stacked stone foundation show any such proof of a tunnel that was covered over.  The 2 boilers in the carriage house are the size of a train engine. The second boiler was NEVER fired it was there for redundancy. The boilers sit below ground level and have an 8-10 inch main that lead into the main house for heat. I was told that the snow never accumulated over the area that the pipe ran. The steam from the pipe kept the ground from freezing. The house has a complex amount of chimneys, cold air returns, and heat ducts. They work in combination with the steam heat, radiators, and multiple fireplaces. There was a separate smaller boiler in the house that was installed for the conservatory that Mrs Sorg had, and was removed at a later date after the sale of the house. I have also read that there was a power station in the carriage house that powered the Sorg Estate, the US Hotel, and the Sorg Opera House. That is another part of Middletown folklore.