NANCY CREEK TUNNEL 
Report as of May 24, 2002

This is the third Report on the above subject. Should you wish to receive the first two, please e-mail me with your request. As before, I am reporting events to the best of my recollection and I will try to differentiate when I am offering an opinion. This Report may not be the position of the Technical Advisory Committee nor the City of Atlanta. 

Today, the Technical Advisory Committee met at the Sutton shaft of the Chattahoochee Tunnel. This is the tunnel that Cobb County is currently building and it is very similar to the Nancy Creek Tunnel. Cobb has created a website that may be viewed at www.chattahoocheetunnel.com. There are two Tunnel Boring Machines at work and therefore, two faces. I cannot report anything about surface noise above where the TBM is working because it was shut down when we emerged. But you can look at the website, figure out its current location and go and listen for yourself. Please remember that the face advances about 40 feet per day.

The Committee was able to descend into the access shaft and walk along a 16 diameter foot concrete lined and a non-lined section. We also walked through an 8 foot diameter intake tunnel to an intake chamber. I was impressed with the overall size of the underground operation wish to highlight several things. First, there was surprisingly little water seeping into the Tunnel in both the lined and non-lined sections. The engineers report that the Tunnel infiltration criteria are 2 gallons per diameter inch per mile per day. I calculate that this will result in flows amounting to around 3600 gpd. These small flows can easily be handled by pumping into existing sanitary sewer mains during construction and can easily be treated at R. M. Clayton upon completion. Second, the tunneling and concrete lining operations were being conducted simultaneously. When we were there, the liner was curing so there was no concrete being pumped into the shaft but it pointed out to me that concrete trucks and rock removal trucks will be arriving and departing from the Roswell shaft simultaneously. Third, the material coming out of the shaft is much more small-grained and wetter than I thought it would be. I believe that the loading operation will not be as noisy and dusty as I originally thought.

It is expected that City Council will authorize this contract on June 19, 2002 and that a Notice to Proceed will be issued by July 1, 2002. The City is insisting on the contractor's compliance with the bid documents with respect to staging. That is to say that Obayashi will start simultaneously with two TBM's from R. M. Clayton and from Roswell and will bore in a northeasterly direction. Obayashi will not be required to re-stage at Roswell and bore southeasterly but this remains an option. It will take 4 - 8 months to blast the access shafts at Roswell and R M. Clayton. By this time, the two TBM's will be transported and installed to begin tunneling. The contract schedule has been extended from 1100 days to 1200 days or October 31, 2005. The EPD Consent Decree deadline is August 31, 2005 and the City will likely get an extension to this date. This would delay the onset of fines but would not likely delay any moratoria. 

More Questions and Answers: 

Q: How much did Cobb County pay for easement rights?

A: $200.00 plus $1.00 per lineal foot. 

Q: What precautions will be taken to protect houses and businesses?

A: A pre-construction survey will be conducted on all structures that are likely to be affected. This will include all buildings within 200 feet of the centerline of the Tunnel and all buildings within 1000 feet of any blasting operation. Should damage occur, the amount will be determined by comparison to the pre-construction survey. 

Q: How wide will the easement be?

A: Along the Tunnel, the construction and permanent easement will be 50 feet, that is to say, 25 feet on either side of the Tunnel.