GAI Consultants, Inc. recently partnered with Carolina Gas Transmission Corporation (CGT) to complete one of the longest horizontal directional drill (HDD) projects in the world.
In early 2010, Carolina Gas Transmission Corporation, a SCANA company, set out to replace a nearly two-mile-long segment of its existing 16-inch natural gas transmission pipeline in Berkeley County, South Carolina.
The proposed CGT project, referred to as the “Cooper River Pipeline Replacement Project,” required the installation of a 16-inch-diameter replacement pipe by conducting 9,889 feet of horizontal drilling at least 40 feet beneath the Cooper River, a significant tidal river in South Carolina. The project location is approximately 17 miles upstream of the Charleston Harbor on the west and east riverbanks of South Carolina Electric & Gas Company’s Williams Electric Generating Station and Nucor Steel Construction Plant properties, respectively.
The objective was to replace the original pipeline, which was installed in 1970 and required ongoing rehabilitation due to the eroding effects of the river. CGT led the initiative to install the pipeline below the 1,089-foot-wide Cooper River. The full pipeline installation – nearly two miles of steel – was accomplished by a single pullback into the borehole. Approximately 6,000 feet of pipe was initially pulled into the borehole, and the remaining 4,000 feet was welded on to complete the pullback. The project also included the installation of two new mainline valves on the east and west riverbanks.
CGT contracted GAI to provide environmental permitting and compliance support for the project. During the initial stages, GAI secured environmental permits, clearances, and approvals including U.S. Army Corps of Engineers Section 404 and 10 authorization, U.S. Fish and Wildlife Service and State Historic Preservation Office clearances, State Construction in Navigable Waters Permit, State Water Quality 401 Certification, and local construction stormwater approvals, to name a few.
In mid-October 2010, CGT began the 6-8-week drilling process, which immediately presented several challenges for the project team to tackle. First, the team had to identify water sources that could supply the drill operations with more than 300,000 gallons. The solution was to utilize the Williams Electric Generation Station fire suppression system for drill activities occurring on the west riverbank side, and the installation of a six-inch-diameter temporary groundwater well on the east riverbank with three frac tanks to store water.
While one problem was resolved, another was presented. Using two drill rigs (one on each side of the river) to complete the nearly two-mile-long bore, drilling operations generated more than 800 tons of mud. GAI assisted CGT in implementing plans to temporarily store, transport, and dispose 1.6 million pounds of drill mud, which had to be taken to a landfill more than 50 miles away from the project site. Other on-site efforts included planning the workspace for pipe fabrication, constructing a temporary pipe bridge over the main entranceway of an LNG Plant, and installing approximately 800-1000 wooden cross-tie mats in the wetlands to support welding, x-raying, and coating equipment as well as pipe rollers and side booms.
GAI’s environmental inspectors also played an integral role in the project’s success. By providing on-site environmental monitoring and inspection, GAI was able to assist CGT in ensuring that the project complied with permit conditions and project plans.
Final clean up and restoration is anticipated to be completed by the end of the first quarter in 2011. With pipe fabrication workspace included, the Cooper River Pipeline Replacement Project stretches nearly 3.5 miles, making it one of the longest HDD projects in the world.
GAI's services included:
- NEPA compliance
- NPDES permitting
- 404/401 permitting
- Threatened and endangered species habitat survey management
- State and local environmental permitting and clearances
- Construction support, including environmental inspections
- Engineering design for temporary drill mud storage basin
For more information, please contact Melvin Stroble, GAI-Charlotte Senior Environmental Manager and Project Manager, at 704.731.1442.