Cold Water Drilling – Relief from Condition 67(g)
Condition 67(g) of the Certificate of Public Convenience and Necessity OC-065 for the Coldwater River located at Kilometer Post (“KP”) 954 in Spread 5A requires Trans Mountain Pipeline ULC (“Trans Mountain”) to file geotechnical and feasibility studies for trenchless watercourse crossings. Trans Mountain filed an application seeking an order relieving it from this obligation for Crossing C20738.
The CER granted the relief sought. Trans Mountain is not required to provide a Geotechnical Report and a Horizontal Directional Drilling Feasibility and Design Report for Crossing C20738.
Trans Mountain indicated that it intends to employ a new contingency method for trenchless crossings. The new contingency method provides flexibility to execute the crossing at any time while maintaining the existing instream window if needed in early 2023. Trans Mountain advised that Crossing C20738 was short (69 meters) and will be executed using the guided horizontal auger bore (“GHAB”) method. Trans Mountain stated that typically, GHABs are completed without detailed geotechnical investigations, rather, test-pits or auger bores are used to identify the materials present at the depth of the crossing and to identify conditions present that would indicate a need to change techniques. The CER noted that a geotechnical feasibility study was completed with the proposed GHAB crossing methodology and alignment, the closest borehole to the crossing is situated on the north bank of the river and is within the GHAB path.
The CER also noted that upon opening the launch and receiving pit excavations for the GHAB crossing, the geology at the Coldwater River crossing will be confirmed by Trans Mountain using the excavations as ‘test-pits’. Trans Mountain stated that the GHAB technique is suitable for construction in cohesive (clay-like) and cohesionless (sand and gravel-like) conditions. Neither soft cohesive nor boulder-containing cohesionless ground conditions are anticipated at the Coldwater River crossing at KP 954. Trans Mountain stated that if saturated conditions are encountered, these conditions can be mitigated.
The CER was satisfied that Trans Mountain provided appropriate rationale for the relief sought and granted the application. The CER reminded Trans Mountain that Condition 67(g) applies to all remaining trenchless watercourse crossings.