FERC issued a favorable final environmental impact statement (EIS) Friday for TransCanada Corp.’s Mountaineer XPress and Gulf XPress expansion projects, a move likely to encourage producers hoping for more natural gas pipeline capacity out of the Appalachian Basin.

Federal Energy Regulatory Commission staff concluded in the EIS that while both projects would result in adverse environmental impacts, “if the projects are constructed and operated in accordance with applicable laws and regulations, the mitigation measures discussed in this EIS, and our recommendations, these impacts would be reduced to acceptable levels.”

Mountaineer XPress [CP16-357] contemplates adding 164.5 miles of new 36-inch diameter pipe and 6 miles of new 24-inch diameter pipe to expand Columbia Gas Transmission LLC’s system in West Virginia. The project would also include three new compressor stations located in Doddridge, Calhoun and Jackson counties, WV; two new regulating stations located in Jackson and Cabell counties; and various other facilities, upgrades and replacements.

The Gulf XPress [CP16-361] project would add seven new compressor stations — three in Kentucky, two in Tennessee and two in Mississippi — to expand the capacity of Columbia Gulf Transmission LLC’s system. The project would also include upgrades to an existing compressor in Carter County, KY, and an existing meter station in Boyd County, KY.

Mountaineer XPress would add about 2.7 Bcf/d of capacity to the Columbia Gas system and is designed to allow additional volumes of Marcellus and Utica shale gas to reach markets in the Midwest, Northeast, South and Gulf Coast. Gulf XPress would add about 875 MMcf/d of new capacity on the Columbia Gulf system to deliver to receipt points in Mississippi and Louisiana.

Columbia Gas and Columbia Gulf are both subsidiaries of TransCanada.

Columbia has said it plans to place Mountaineer XPress into service by October 2018, with construction expected to begin this fall. Gulf XPress appears likely to follow a similar timeframe, based on informationpreviously provided by the company.

The EIS brings Mountaineer XPress and Gulf XPress one step closer to a certificate order from FERC, but the Senate will need to restore the Commission’s quorum before any new natural gas pipeline projects can be approved for construction.

The lack of a quorum has not stopped FERC from completing environmental reviews this summer. The Commission’s environmental staff has kept busy recently, issuing favorable reviews for the Atlantic Coast and Mountain Valley pipelines, two other highly anticipated Appalachian takeaway projects looking to enter service over the next couple years.

Management for Mountain Valley Pipeline backer NextEra Energy Inc. said during a recent earnings conference call that the project will be delayed if the Commission can’t issue a decision on its project application by September.

Marcellus and Utica producers will be hoping FERC can get back to full strength soon, as pipeline constraints have taken a toll on regional prices. The familiar Appalachian basis differentials of the past few years have returned this summer after a brief respite earlier this year.

Dominion South has been trading at more than a dollar discount to Henry Hub for the past week, a significant erosion from differentials of around 20 cents observed as recently as May, according to Daily GPI prices.

The widening differentials come as Appalachian production has increased over the past few months, perhaps a reflection of producers anticipating new takeaway capacity hitting the market this year. But one of the biggest projects scheduled for service in 2017, Energy Transfer Partners LP’s 3.25 Bcf/d Rover Pipeline, has encountered regulatory setbacks.