Frequently Asked Questions

  • A tunnel system is being used due to the historic and extensive development that has occurred on the Charleston peninsula. There is not enough space available at the ground surface to adequately address the needed drainage improvements. The use of a deep tunnel system avoids existing surface structures and surface utilities.

  • This project was identified as a priority due to the current impacts of flooding to the local community including residences, businesses, hospitals, and transportation.

  • The construction of the drainage improvements will ensure less frequent and less extensive flooding. This project also includes components that improve the streetscaping along the Septima Clark Parkway and adjacent roadways.

  • Construction of Phase 1, which started construction of the Project, commenced in 2011 and was completed in 2013. Phase 2 was started in 2015 and was completed in 2017. Phase 3 began in 2016 and finished up in 2020. Current construction on Phase 4 is expected to be complete in 2022. Phase 5, which concludes construction of the Project with the installation of the pumps and pump station superstructure, is expected to be complete in 2023.

  • Aside from some minor work to sever the new system from the existing tidal system at the end of Phase 4, all remaining work will occur between the US17 overpasses adjacent to the Ashley River.

  • Large diameter (20ft to 30ft) concrete shafts are constructed to depths ranging from 120 to 170ft below ground level. A tunnel boring machine (TBM) is used to excavate the ground starting from one shaft and terminating at another shaft. As the TBM excavation progresses the ground is temporarily supported with lumber and steel. Once excavation is complete, concrete is placed to permanently support the tunnel; the tunnel ultimately acts as a large concrete pipe at the completion of construction.

  • For Phase 4, construction consists of driving piles to support the pump station and outfall structures, excavation of soil to accommodate concrete placement for the pump station and outfall structures, construction of the wetwell and outfall, construction of a silt removal unit, installation of silt removal pumps, and installation of bar screens to remove trash before the water is discharged to the Ashley River. Phase 5 will consist of installation of the large stormwater pumps, each capable of pumping 120,000 gallons per minute, and construction of the pump station superstructure.

  • Construction activities are monitored to determine impacts from light, sound, vibration, and ground movement. Construction activities are limited to daytime hours only when possible.

  • The Contractor must follow applicable OSHA standards and City ordinances regarding noise levels. Construction activities are limited to daytime hours only when possible. Construction activities occuring during nighttime hours are staged to minimize noise when possible.

  • Signage will be posted at each of the project sites. Fencing is installed around the perimeter of all construction sites to prevent public entry. Additional security measures are installed at the shaft locations to prevent accidental falls once onsite.

  • If there is an immediate concern related to health or property, call 911. Otherwise, call the City of Charleston at 843-724-7311.

  • We encourage you to ask questions throughout the project! If there is an immediate concern related to health or property, call 911. Otherwise, call the City of Charleston at 843-724-7311.

  • Email citizenservices@charleston-sc.gov and request to be added to the Project e-newsletter.