Client project details

Columbia Gas Transmission Corporation (New Market, VA) (Karst Sinkhole Evaluation Using Geophysics)

The Project

The investigation conducted by EGGI was prompted by the discovery of sinkholes near a section of natural gas pipeline that is owned and maintained by the Columbia Gas Transmission Corporation (CGTC) in New Market, Virginia. The development of the sinkholes appeared to be related to the installation and development of a nearby high-capacity bedrock well. The occurrence of the sinkholes caused the CGTC to investigate the potential for additional sinkholes to develop underneath the gas pipeline. This 24-inch-diameter pipeline operates at a maximum pressure of 877 pounds per square inch (psi) and is a major supplier of natural gas for the City of Richmond, Virginia. Therefore, the future integrity of the pipeline was a matter of public safety and substantial economic concern.

The work tasks that EGGI performed in this investigation included the compilation of background hydrogeologic data, a lineament and bedrock fracture-fabric assessment, and a detailed geophysical investigation of the subsurface, both parallel and perpendicular to the gas pipeline, using electrical resistivity methods.

Status/Results:

Modeling of the electrical resistivity data collected during this study showed that the carbonate bedrock proximal to the pipeline was riddled with solution caverns and bedrock troughs. Based on the geophysical models and other hydrogeologic data collected and reviewed in this study, EGGI concluded that, at this specific site, continued artificially-induced water level fluctuations associated with the pumping of the high-capacity bedrock well would pose a high risk potential for additional sinkholes to form beneath or proximal to the CGTC pipeline. Dimensions of future sinkholes were estimated to potentially extend beyond 45 feet in width and 20 feet in depth. These data prompted CGTC to develop a mitigation plan to improve the overall protection of this gas pipeline from potential collapse.

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The work tasks that EGGI performed in this investigation included the compilation of background hydrogeologic data, a lineament and bedrock fracture-fabric assessment, and a detailed geophysical investigation of the subsurface, both parallel and perpendicular to the gas pipeline, using electrical resistivity methods.

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