Tenders will be invited in July 2003 for the construction of phase 1 of the outfall augmentation sanitary relief sewer as part of the Big Walnut Augmentation Rickenbacker Interceptor (BWARI) project in Ohio, US.

Phase 1, designed by URS Corporation for the City of Columbus in Ohio, US, calls for a 6.4km long, 4.3m diameter tunnel. It will be constructed using an EPBM, provided by the successful contractor, through Glacial tills and Outwash deposits.

Phase 2 will be up for tender in 12 months time. This will involve the construction of a 4.8km long, 3.7m diameter tunnel.

On both phases, the most challenging aspect will be the geological conditions. The contractor will have to handle ground with cobbles and boulders, while having to deal with a high water content. Ground water levels cannot be disturbed during the construction period.

The tunnels will be lined with pre-cast concrete segments with a corrosion-proof lining that will protect against any damage caused by sewer gases.

The estimated cost for the whole project is US$200M+.