42-Inch Sanitary Sewer Relocation Diversion without Bypass Pumping

The Florida Department of Transportation (FDOT) proposed improvements to Interstate 275 within the City of Tampa. The Interstate improvements necessitated the adjustment of numerous City of Tampa wastewater collection facilities including the Clark Avenue Interceptor; a 42-inch diameter, plastic sheet lined, reinforced concrete pipe (RCP), gravity flow sanitary sewer with approximately 15 MGD average daily flow. Relocation of approximately 660 linear feet of Interceptor was required. Bypass pumping, would have required either a temporary pipeline crossing the active highway (aerial or trenchless) or a lengthy route down the highway to an existing overpass and back that would also require crossing active traffic lanes of other roads. As a result, an alternative flow diversion method was considered during the design. To connect the new portion of 42-inch sewer to the existing sewer without interruption of the flow, two diversion structures were employed. A rigorous sequence of construction for the construction of the plastic sheet lined structures allowed the transition from connecting the new sewer, cutting into the old sewer within the structure, diverting the flow, and permanent completion of the facility. The method uses a flow tube approximately 30-inch diameter with special inflatable seals at each end to seal between the existing 42-inch ID and the 30-inch OD. The seals look like heavy duty tire inner tubes. The project was completed successfully with a few lessons learned including a solution to regulatory problems of emitting hydrogen sulfide (H2S) gases from the wastewater stream, a clever more flexible microtunnel boring machine and even a handy new epoxy gel/paste product that successfully adheres to plastic sheet (PVC) as well as just about anything else.