Business NewsRough seas cause construction challenges at AltaGas export facility in B.C. Rough seas at propane portPhoto: Ridley Island Energy Export Facility / Facebook Rough seas are slowing construction at a propane export terminal outside Prince Rupert, B.C. Rough seas have been posing challenges for AltaGas Ltd. as construction on its propane and butane export terminal on British Columbia's north coast nears completion. "While onshore execution has been ahead of plan, in-water construction has proven more challenging due to maritime conditions and weather delays," chief executive Vern Yu told analysts on a conference call. As a result, onshore efficiencies are no longer expected to fully offset higher in-water construction costs."