In a bid to stop enlargement of a transmission corridor through three units of the National Park System, a coalition of conservation groups has asked a federal judge to halt the project.

At stake is whether Pennsylvania Power and Light Electric Utilities and Public Service Electric and Gas Company will be able to replace an existing 230kV transmission line across the Appalachian National Scenic Trail, the Middle Delaware National Scenic and Recreational River, and the Delaware River National Recreation Area with a double circuit transmission line carrying a new 500kV line.

According to the Park Service, the Susquehanna-Roseland power line proposal includes the replacement of an existing transmission line with an approximately 145-mile long 500 kV transmission line from the Susquehanna Substation in Pennsylvania to the Roseland Substation in New Jersey, and several 500 – 230 kV substations in both Pennsylvania and New Jersey. Fewer than five miles involve Park Service lands.

The new transmission line will largely follow the route of an existing 85-year-old power line, but the new towers reportedly will rise more than twice as high as the existing towers and would include clearing substantially more trees and the construction of access roads through the parks.

Earlier this fall many members of the same coalition -- the Appalachian Mountain Club, Appalachian Trail Conservancy, Association of New Jersey Environmental Commissions, Delaware Riverkeeper Network, New Jersey Highlands Coalition, New York–New Jersey Trail Conference, National Parks Conservation Association, Rock the Earth, Sierra Club, and Stop the Lines -- sued National Park Service officials for approving the project.

On Thursday they returned to court with the request for an injuction to halt work on the project until the judge can consider claims that the power line will cause irreversible ecological and scenic damage.

The coalition maintains that the 500KV power line would slice through the parks, "impairing spectacular scenery, damaging rare geological and ecological resources, and marring the recreational experience for the more than 5.2 million people who visit the Delaware Water Gap National Recreation Area each year."

The Park Service's approval of the project contradicts the agency’s governing mandate to protect the National Park System “unimpaired for future generations” as required by the 1916 National Park Service Organic Act, the groups contend.

Construction and pre-construction activities have already begun on segments of the transmission line in New Jersey and Pennsylvania, according to the coalition.

In a July 2012 environmental impact study conducted for the NPS, the human use and ecological impacts from the project were estimated to cost $89 million.

“The National Park Service has approved a project that is poised to permanently damage treasured public resources. Construction-related activities in the Delaware Water Gap could begin at any time, and if a preliminary injunction is not granted, the damage will be done before the court even gets a chance to decide the claims that are before it,” said Hannah Chang, attorney with the public interest environmental law firm Earthjustice, representing the conservation groups along with the New Jersey-based non-profit Eastern Environmental Law Center. “The circumstances here demand that construction be put on hold for now, so that the court at least has an opportunity to consider the claims raised.”

In a release announcing the filing for the injunction, the groups said the project threatens "the Delaware Water Gap’s spellbinding views, pristine environment, and diverse wildlife that include bald eagles, peregrine falcons, and black bears. The Delaware Water Gap National Recreation Area was named a Top 10 most-photogenic national park for fall foliage, and is the eighth most visited national park unit in the country."

Cinda Waldbuesser, a program manager of the National Parks Conservation Association, noted that in its Final Environmental Impact Statement on the project the Park Service noted that the project would "‘degrade the integrity of resources and the scenic landscape’ in the parks and ‘appreciably diminish key aspects of the parks’ that visitors enjoy.”

“That clearly violates the Organic Act which requires the agency to 'conserve the scenery' and protect park resources from impairment," she added. "We intend to hold the National Park Service accountable to their core park preservation mission.”