sentences:  The two leaves (north and south) were built off-site and floated on the river to Wells Street for installation.The other half of the bridge was rebuilt in place – the two portions closest to each river bank, containing the counterweights for the bascule bridge.The second period of the reconstruction that affects Chicago Transit Authority train service on the upper level began at 10 pm April 26, 2013 and ended before the morning rush hour Monday May 6, 2013.