Isolation and Condition Assessment of the 36-inch Effingham Interceptor Force Main

Purpose: Share the background and successful implementation of a multi-phase force main isolation, condition assessment and rehabilitation project in a congested urban corridor in southeast Virginia. Abstract: HRSD committed to replace air vents with galvanized riser pipes vulnerable as a material risk of failure. An air vent was discovered directly tapped into a pressurized in-line concrete vault located on a low-pressure 36-inch diameter reinforced concrete interceptor force main serving the City of Portsmouth and the Norfolk Naval Shipyard. The vault was installed as part of a 1950s force main relocation project to facilitate force main diversion/relocation required to construct Interstate 264 and the Downtown Tunnel connecting the Cities of Portsmouth and Norfolk. The newly found vault and associated force main provided over 60 years of service in a likely corrosive environment raising concerns of the vault's condition as a high point in the system as well as the interceptor force main it serves. Project challenges included discovery of an inaccessible in-line pressurized concrete vault beneath a heavily traveled roadway near an interstate interchange and a second inaccessible vault at the other end of the relocation, a lack of operational isolation valves along the force main, seasonally high flows received from the Naval Shipyard, force main isolation pump and haul requiring over 100 trucks strategically staged and hauling from multiple locations, and potentially encountering heavy metals contaminated soils associated with a nearby superfund site. Alternatives to remove the air vent and vaults were evaluated including isolation of the vaults with line stops, bag stops, pump and haul, and an above ground HDPE bypass force main. Trenchless force main rehabilitation methods considered included CIPP Liner, compression fit pipe and slip lining. Installation of a new force main parallel to the existing force main and a new force main located on CSX railroad property along with abandonment of the existing force main were also evaluated. Projects costs were estimated between $1,800,00 and $4,700,000. Results of a triple bottom line feasibility analysis suggested a two-phase project approach featuring Phase 1 force main improvements, isolation by construction of a temporary force main diverting flows to another force main and condition assessment followed by Phase 2 force main condition-based rehabilitation. The primary benefit of this approach was to confirm candidacy for force main rehabilitation and as-built construction conditions for trenchless technology suitability assessments and, if possible, competitive bidding of rehabilitation methods. The Phase 1 project included certain alternate bid items to facilitate continued construction activities to accommodate a Phase 2 rehabilitation contractor. This presentation will highlight coordination efforts required for preparation of the alignment study, construction of the Phase 1 force main isolation improvements and condition assessment results, the trenchless technologies considered, and the Phase 2 rehabilitation approach. Construction of the Phase 1 isolation improvements is progressing with isolation scheduled for completion in January of 2023, followed by condition assessment including cleaning, CCTV inspection and laser pipeline profiling and mapping in February of 2023. Dependent on the condition assessment results, HRSD's plans to award a force main rehabilitation contract by the summer of 2023. Isolation of the force main will remain in place for removal by the Phase 2 contractor upon successful completion of the interceptor force main rehabilitation improvements. The in-line 1956 vintage in-line sewage diversion vaults will ultimately be dismantled/abandoned.