Construction of the shafts at the CSO sites, to transfer flows from the existing sewer to the tunnel, would vary depending on the depth, the amount of flow they need to carry and the geology. The shaft would be a concrete cylinder with an internal diameter of and deep. Ventilation structures at CSO sites to allow air in and out of the shaft were also required. Construction at these sites was expected to take between and years and once complete each site would be landscaped.