For decades the TransCanada Mainline was used to export natural gas from western to eastern Canada and into New York State, but the eastern portion of this pipeline is now being used to import natural gas from New York into eastern Canada.
The Niagara and Chippawa terminals were modified and now mainly import gas. Niagara was modified in 2012 and Chippawa was modified in 2015.
TransCanada Pipelines Limited received National Energy Board approval to modify its Iroquois export terminal in November 2017. The modifications would allow the Iroquois terminal to switch from an export point to mainly an import point, although it could function as either.
The switch from exports to imports is partially explained by the rapid growth of shale gas production in the Appalachia region in northeastern United States, which includes the Marcellus and Utica basins.
This area has accounted for most of the U.S. production growth over the last decade, increasing from very little production in 2009 to almost 27 billion cubic feet per day of dry gas production in March 2018.
Some of the Appalachian gas now feeds the eastern U.S. market, displacing some of the gas supplied by the Western Canada Sedimentary Basin gas via the Niagara, Chippawa, and Iroquois terminals.
Natural gas exports at Iroquois decreased between 2009 and 2017. Although gas throughput is seasonal, declining exports are most notable in the summer months, when throughput is the lowest. These exports have been mainly displaced by U.S. Appalachian natural gas production.
In response to increased shale gas production in the Appalachian area, several pipeline proposals and modifications have either been approved, or are in the regulatory approval process under the U.S. Federal Energy Regulatory Commission (FERC)