A federal appeals court has upheld New York’s water-quality approval for a major natural gas expansion, rejecting an environmental challenge to a key permit for the more than $1 billion Northeast Supply Enhancement pipeline project.

The U.S. Court of Appeals in New York City ruled Aug. 21 in favor of the New York State Department of Environmental Conservation, leaving intact its Clean Water Act Section 401 certification.

Developer Williams Cos., through subsidiary Transcontinental Gas Pipe Line Co. (Transco), broke ground April 14 and targets entering service in the fourth quarter of 2027.

The expansion will add roughly 37 miles of pipeline and related infrastructure across Pennsylvania, New Jersey, and New York, increasing capacity by 400,000 dekatherms per day to serve National Grid customers in New York City and Long Island.

The pipeline buildout includes 10.1 miles of 42-inch-diameter line in Pennsylvania and 26-inch-diameter segments in New Jersey and Queens.

Crucially, about 23 miles run offshore in Raritan Bay and New York State waters, including a 17-mile crossing of New York Harbor.

The project also adds a new 32,000-horsepower compressor station in Somerset County, New Jersey, and an electric motor-driven compressor in Chester County, Pennsylvania.

An environmental coalition—including NY/NJ Baykeeper, Sierra Club, and the Natural Resources Defense Council—argued the state inadequately justified approving the project in 2025 after rejecting a similar application in 2020.

That earlier denial cited concerns over disturbing mercury- and copper-contaminated sediment, clam habitats, and pipeline burial depth.

However, the court found Transco provided updated technical records addressing past issues.

Revised survey data corrected initial hard-clam density estimates, while additional data showed deeper burial was unnecessary for gas lines and could increase sediment suspension.

The court also rejected claims that environmental safeguards were improperly deferred, noting the permit sets strict pollutant limits, continuous water-quality monitoring, and independent stop-work authority.

State officials confirmed no additional state permits are required, stating they remain committed to closely monitoring construction to protect local waterways.