A new transmission line that would carry electricity across a four-mile span of the James River has received a federal agency’s long-awaited nod of approval. But the $270-million undertaking still needs to earn permits at the state and local level this summer, and it is expected to continue facing vocal opposition from environmental and historic preservation groups.

After reviewing for nearly four years Dominion Energy’s plans to run a 500-kilovolt power line on towers across the river, the U.S. Army Corps of Engineers issued a preliminary permit for the project on June 12. The Corps’ final permit is contingent on approval from the Virginia Marine Resources Commission, the Virginia Department of Environmental Quality and the James City County Board of Supervisors.

The project was to be discussed at the VMRC’s meeting June 27 and at the James City County board’s July 11 meeting.

Historic preservation and environmental groups have opposed the project for years. They say the power lines strung across towers, two of them nearly 300 feet tall, would mar an otherwise unaltered view of the James River from several historic sites and that viable alternatives have not been fully considered.

In April, the Corps published a memorandum of agreement with Dominion, the Virginia State Historic Preservation Office and the federal Advisory Council on Historic Preservation, detailing how the power lines’ impacts on historical and environmental resources would be mitigated with $90 million worth of projects funded by Dominion.

Dominion officials say the transmission lines are necessary to continue supplying power to a projected 600,000 residents of the Virginia peninsula, where they are closing a coal-powered plant in Yorktown.

“Our goal is to find a solution that minimizes or mitigates as much as possible the impact on the historical and environmental resources in the region,” said Dominion spokeswoman Bonita Billingsley Harris. “We believe this accomplishes that goal, and we hope (the deciding agencies) will recognize that as well.”

Stringing high-voltage lines across the river is part of the company’s larger project to meet increased demand for electric power in eastern Virginia, and in particular the densely populated Newport News and Hampton areas. The Virginia State Corporation Commission first approved Dominion’s plans in 2013.

The new lines would carry electricity from Dominion’s Surry Nuclear Power Station, which straddles the Hog Island Peninsula just downriver from Jamestown Island, to a switching station near Skiffes Creek in James City County before being transmitted across the region. The county’s board declined to sign onto the Corps’ agreement for mitigating the project’s impacts. But the county remains a consulting party on the project, and opponents hope local officials will send a major component of the power-line plan back to the drawing board.

The Surry-Skiffes Creek project, as it’s called, has already cleared significant legal hurdles, including review by the Virginia Supreme Court. While that court approved the need and scope for the proposed project and Dominion’s planned route as the least costly, it also agreed that James City County would have to make a land use decision to allow the switching station.

Dominion needs a special use permit or rezoning from the county to construct the station, and board members have questioned whether the county’s historic lands are the right place for it.

James City County is part of the “historic triangle” of Virginia, named for the economically significant historic tourist destinations of Jamestown, Yorktown and Williamsburg and national historic landmarks like Carter’s Grove plantation.

The Corps’ memorandum of agreement directs Dominion to spend $90 million on mitigation projects — such as shoreline protection at the historic Jamestown Island, Colonial Parkway and Carter’s Grove sites — and reducing, where possible, the impact of power-line construction on those sites.

It also details the project’s environmental impact, including construction that would impact more than 2,700 square feet of river bottom, discharge fill material into nontidal wetlands and convert a half-acre of forested wetlands into shrub habitat.

The mitigation plan agreed upon by the Corps, Dominion and other stakeholders also includes setting aside emergent marsh land next to the Chickahominy Wildlife Management Area as one of several water quality improvement projects along the James River. Still, groups that oppose the project say mitigation measures won’t undo the damage caused by unsightly power lines across this segment of the river.

“You couldn’t pick a worse place to build industrial infrastructure,” said Sharee Williamson, associate general counsel at the National Trust for Historic Preservation. The nonprofit released a 55-page report in February detailing alternatives to Dominion’s plan that the group contends would better preserve the James River landscape as it has been for 400 years.

The organization got involved in 2013, when the power-line project put that stretch of the James on its list of the 11 most endangered places in the United States. The trust has partnered with more than a dozen local and national organizations opposed to the project, arguing for alternative routes or methods for getting additional electricity to the Peninsula.

Suggested alternatives include reworking the Yorktown plant so that it continues to provide power to the Peninsula during peak seasons or on a standby basis, finding another route for the power line or running it under the James River, rather than over. The trust’s report says that rehabilitating the Yorktown plant, in particular, would cost less than Dominion’s current plan.

“We still believe [these alternatives are] the right course of action,” Williamson said, “and we’ll continue to use all available venues to make sure that one of the most historically significant landscapes in the United States is protected.”

Dominion officials said they’ve considered dozens of alternatives to the current plan over the years but that none accomplishes the same electricity-generating goals while limiting the cost passed on to ratepayers and the impact on local resources.

Dominion’s Billingsley Harris said the switching station in James City County is key to the overall project, which already has faced a protracted approval process to bolster power sources that were expected to become inadequate starting in 2015.

Dominion also said that any further delays could result in rolling blackouts during peak electricity use time in the Newport News-Hampton area.

Because of ongoing delays, Dominion has had to get several extensions from federal regulators on its plans to close the Yorktown coal operation, and, last month, was given permission to fire it back up to meet the increased electricity demands of summer. PJM, the multi-state transmission authority responsible for the reliability of the power grid, has required Dominion to use the station’s coal– and oil-powered units as needed for a 90-day period to help meet the region’s electrical needs.

If the new transmission line across the river gets final approval, Dominion officials estimate it will take 18–20 months to complete construction.