Construction of large, complex facilities to convey and treat combined sewage began with the 3.5-mile long Columbia Slough Consolidation Conduit, which went into service in 2000, followed by the 3.5-mile, 14-foot diameter West Side CSO Tunnel and the Swan Island CSO Pump Station in 2006, and finally the six-mile long, 22-foot diameter East Side Big Pipe in 2011.