St. Clair River Line 6B Pipeline Replacement

GeoEngineers spanned an international border with this challenging HDD pipeline replacement.

Enbridge is a Canadian company that operates the world’s longest crude oil and liquids transportation system. One of the company’s pipeline safety inspections revealed an anomaly that regulators deemed potentially hazardous in the section of Enbridge’s Line 6B pipeline running 40 feet below the St. Clair River channel between Marysville, Michigan, USA and Sarnia, Ontario Province, Canada. The crossing point is about seven miles south of the Bluewater Bridge, a major international border crossing that links the United States and Canada at the point where the St. Clair River flows out of Lake Huron.

Enbridge decided to employ the horizontal directional drilling (HDD) method to replace the 3,195-foot-long, 30-inch-diameter, steel pipeline and hired GeoEngineers to provide HDD design and consulting services. This highly visible international project would receive heavy scrutiny from regulatory agencies in both Canada and the United States, so Enbridge needed everything to go right.

Several factors made this HDD project formidable. The hurdle of coordinating between the nine regulatory agencies representing two countries was made even more challenging by the high risk for hydraulic fracture during drilling at the site. Hydraulic fracture occurs when the pressure required to keep drilling fluid flowing through the hole underground causes the surrounding soil to expand and eventually fracture, allowing drilling fluid to escape the HDD hole and potentially flowing into the river.

Regulators required turbidity testing in the river on both sides of the HDD to monitor for drilling fluid escaping into the river. In addition, the geometric design of the HDD alignment and profile had to avoid numerous existing pipelines, utilities and underground structures. The obstacles included the existing Line 6B, which was located just 10 feet from the entry point, a 20-foot-deep sewer line crossing the HDD alignment near the entry point, steel pilings supporting a large pier on the Canadian side of the river and an existing pipeline also installed using HDD methods that crossed the Line 6B HDD alignment. (YETI)

GeoEngineers completed its work for Enbridge in three phases. In the first phase, our team recommended the best approaches for accomplishing the HDD and developed cost estimates for construction and GeoEngineers’ HDD design and construction observation services. In the second phase, our team performed geotechnical explorations and created the HDD design and technical reports used in discussions with the client and to satisfy the requirements of the regulatory agencies. In the final phase, GeoEngineers observed and documented HDD construction for Enbridge.


GeoEngineers launched its geotechnical exploration phase of the project by drilling borings on land and over water near the alignment of the proposed HDD. In addition, GeoEngineers conducted a geophysical sub-bottom profiling study of the St. Clair River along the HDD alignment to help determine the thickness of the soils above the shale bedrock along the crossing alignment and to locate any zones of soil which might have contained gravel, cobbles and bouldersThis information was used to modify the depth of the HDD profile so that bedrock was not encountered along the HDD profile.

The soils were found to be consistent with published geology for the area, and the team’s modeling indicated that there was a high risk of hydraulic fracture and subsequent inadvertent drilling fluid returns along the majority of the designed drill path. Inadvertent drilling fluid returns occur when drilling fluid migrates to the ground surface at locations along the HDD alignment. GeoEngineers’ HDD designers lessened the risk of hydraulic fracture in their designs by recommending that the pilot hole be completed by intersecting two pilot holes drilled simultaneously from both sides of the river.

GeoEngineers utilized a sub-bottom profiling survey to aid in the design of the crossing. Using this technique is not common for HDD design purposes, but it was used successfully during the design process to help reduce potential construction-related risks. GeoEngineers also created a unique HDD design video to help explain the HDD design approach to the Enbridge board, building confidence that the pipeline replacement could be achieved as planned. The video showed a 3-D view of the HDD profile and all of the obstacles that would require drilling around, under and between.



The pipeline was safely and successfully replaced, thanks to GeoEngineers’ expert technical and scientific data analysis, HDD design expertise, comprehensive project planning to manage drilling risk, skilled negotiations with US and Canadian regulatory bodies and thorough construction observation and reporting.

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